Jump to content

Garage Diary : Sunbeam Motorcycle resto's..

Recommended Posts


..just finishing up on balancing the weights of piston gudgeon pin and con-rods from yesterday.  .


I started off with ; pistons 8g difference in weight, and a pair of gudgeon pin 2.2 difference in weight.  Matching the heavy piston to the lighter con-rod, and vice versa (as above) still left me with 5.8g difference.   The lighter gudgeon pin looks to be the heavier (above right) but it is straight drilled through whereas the heavier one is drilled hollow as a taper from either end, so is thicker in the centre.    The pistons themselves look to be very similar indeed, and I know that 5.8g of aluminium is physically a lot of metal to remove, so removing that much wasn't really an option. 

Conversely because steel is that much denser I need take less out of the gudgeon pin to achieve a better saving.  So that's what I did.  Starting with the already lighter pin I wondered if I might work the hole through it to be a taper ..and the metal removed would be the weight saving I sought . .

.     P1340250s.thumb.jpg.1ca9c0477629ac9b50c3c2aef7e5ae16.jpg

^ I didn't honestly think it would work, gudeon pins being hardened steel an all,  but I tried to used a burr bit in my cordless drill.  Despite that bit being old and well used (seeing much use in my fibreglass boat) - amazingly it did cut this steel.! 

I steadily worked my way around the inside of either end of this pin ..which did take me three hours,  but yes - it worked. 


^ the pile of grinding is testimony to that. I took 4.6g of weight out of it  ..just in tapering the hole from either end. This brought the gudgeon pin down to 61g which is the same as those I'm using with Pudge's set of pistons & con-rods.  My reasoning of course was that ; if just this amount of metal is good (from standard) with the other gudgeon pins, then it ought to be equally as safe to use in this engine.


^ That's it.. I took just 0.2g out of the heavier piston which brought it down to 221.7g but paired with the 61g gudgeon pin their combined mass is 282.7g.  And this is now just 2.4 heavier than the lighter piston matched to the heavier gudgeon pin.  

And then, pairing the heavier of these with the lighter con-rods for that engine, and vice versa.. there is now just 0.4g difference in their total weight.   B)

I can happily to accept that.   Job Done.!

Cheers, Pete.

Share this post

Link to post
Share on other sites


a week on from my last post., when I was matching the weights of the pistons and rods and carefully gapping the piston rings ..


^ dry fitting the con-rods, with new shells, to the crankshaft to ensure all was well. It was ..but for a slight confusion . .


^ you note #1  con-rod had at some time also been stamped on its other side, so when I first fitted this cap it happened to be on back to front front - so not quite true and binding.  It was soon spotted and corrected though, and I've subsequently scoured across these back-face marks to avoid making the same mistake when working inside the crankcase.


^ No it's not a double-crankshaft four-cylinder engine but two twin-cylinder engine being worked on at once. :)

On the one crankshaft (that at the rear) you might have noticed ( to the rhs) a large screw plug hanging out by its front journal. . .


This 1" screw / core plug closes off the large drilling inside & between the two big ends.  It is designed to come out - so the inside oil gallery can be properly cleaned out. Because that is a centrifugal oil filter..  As the crankshaft spins ; heavy particles within the oil are naturally thrown outwards by the centrifugal force, and eventually build up in there as a very tightly compacted sludge.  The drillings into that gallery for lubrication to the big-end shells are so positioned to allow that 1" dia x 5" long space to be half packed before the oil flow is in any way restricted.  And if the oil is changed frequently - that equates to a monster mileage.  If however oil changes are neglected and filthy heavy black oil is spun - the plug needs to be pulled and the compacted sludge gallery chiseled out.  .. yes it gets that hard.! 


^ the professional who pulled this engine apart removed most every stud and every plug in every part, even though that was neither necessary nor useful. 

What's the big deal with taking everything out.?  Well I come from the perspective of not disturbing things which need not be, unless not touching them is detrimental to the long term well being or reliability of the engine. ..for example ; old oil seals. They may seem to be in good shape but because of its age and their perishing - they ought to be changed.)   Conversely a fastening into the engine needs not be disturb unless it is weak or because the flat is needed for machining.   In this instance a large roller bearing overlaps the core plug and so that needs to be removed first ..and because there is no space behind it to get a decent puller in - they are more often than not damaged.  At £89 +P&P.,  unless it is needed replacing (very rare on these engines) then why risk it ?


^ Before pulling the bearing and taking the core plug out,  you can easily check whether it is necessary to do so.  A curved piece of wire simply poked through the big-end oil drillings can be used to feel if there is a build up of sludge in there. Without packed sludge the wire feels the smooth, hard metal side walls. But if it is full of crud - then the feel is dull and the wire digs into in the surface. 

A parts washer (pumped cleaner) can be used to wash through from the three oil-way drilling to ensure no loose bits are in there.  I left one running overnight because what was inside was soft sludge. And after 14 hours of being pumped with parts cleaner it was fine. 


^ It took me two hours to get this thread needle-filed clean enough to go all the way back in.  


^ before refitting the plug I did however check the drillings for the oil-way to both big-ends was clear.  It was mostly but the correct imperial size of 7/32" revealed it not having been properly cleaned out.


^ Likewise the drilling from the rear main bearing carrier into the crankshaft's gallery. This was furred up a little more ..right near the bottom end, as if someone had run a 5mm drill down into it but even that drill wasn't long enough.  It needs to be the same 7/32" imperial-sized drill which protrudes at least 2-1/4" from the chuck.  Having stripped the engine this far why not just do it ?


^ when the plug's thread is clean and refitted with medium strength Loctite - it does not need to be peened with a centre-punch to lock it.  Btw. you cannot peen the forged steel crankshaft as that's too brittle a material and its edge will tend to crack off. .  

With that done I refitted the studs into the crankcase. . .


^ the studs had their threads checked and then dry fitted first, also cleaned up of gouges where the grips had been used on some of these studs, before being refitted with Loctite.  Again only if necessary are the studs replaced ..as I better trust the quality of the original parts over a replacement.

More to come later with the rear bearing assembly and oil pump, and also trial fitting the cylinder head. .



Share this post

Link to post
Share on other sites


...the rear bearing assembly and oil pump, and also trial fitting the cylinder head. .

well ok then, but in reverse order :blink:


^ Ok no head gasket is fitted but if it doesn't sit down and be reasonably flat ..what hope is there ?


^ I don't know who but someone previous replaced the two rear outside studs with stepped /shouldered ones.  That is, their 5/16" BSW holes have been tapped out to be 3/8" and an aftermarket stud fitted. That's not terrible, although I personally prefer to use helicoil type thread inserts, because they cut less metal away in the aluminium case. However these were screwed in as far in as their hole allowed and that wasn't enough.  In retrospect, I should have taken the thread out again and cut their threaded length down, but instead I countersunk the holes in the underside of the cylinder head, just enough ..perhaps 1/16", so the head would then sit down.   A little scraping with a craft-knife blade flat on the gasket face removed the slight stretch around the studs fitted into the cylinder head. The gap is now less than my feeler gauge so a head gasket will take up any more.  

Tbh., the three 5/16" studs, around the timing chain chimney, barely do anything compared with the nine 3/8" cylinder-head studs.  I guess they are there to help prevent the corners from lifting and so distorting. 

However, the workshop manual says to tighten the main cylinder-head nuts with two spanners (one interlocked to the other ..to double their leverage), but it doesn't exclude nor mention how to tighten the three smaller ones ..which of course strip out with that amount of applied force.        

- - -

Moving on - Rear bearing carrier and oil pump . .


^ The rear main bearing carrier is of cast iron with the white-metal main-bearing pressed into its centre. The crankshaft end float is determined by a flange on the back face of this bearing. The geared oil pump is machined into this casting, which is also drilled with oil ways ; from the sump's pick up pipe, to the rear main bearing (..and crankshaft),  to a machined-in oil pressure control valve (situated to the left of the pump), and to lubricate the spigot (at the top) which carries the geared cam-chain timing wheel (..that has the chain sprocket on its reverse face).  At the top, in its rear face, is an oil-way drilling to the crankcase which leads up to the cylinder head which likewise is drilled to the camshaft and rockers.   So really it is a brilliant piece of (lubrication) system design ..with all but the pipe from the sump and the drilling to the camshaft contained in this one part. B)


^ the components of the oil pump, which as you can see has had it cover (bottom) leveled. The gears themselves just drop in but any end float in those needs to be taken out by removing the two studs and milling the face of that housing. 


^ These gears had a couple or three thou of an inch end float (seen as light through the gap above) ..and I don't have a milling machine. But I did have that craft knife blade and found by scraping that there was a tiny lip around the machined hole ..and with that carefully scraped flat - it removed the gear's end float completely. I was lucky with this one.   :ph34r:

I physically blow into (pressurise) the oil pressure valve ..with just its ball (no spring) in place.  If that ball seals the air-flow when dry of oil - then it's fine for service. 

The pump and its pressure control valve were refitted, checked to be within fine tolerance, and oiled.  I also checked the rear main bearing dry fit onto the crankshaft - it to ensure it was exactly the right size.

- - -


^ It's not what it seems !   :twisted:    My next job was to ensure that the inside of the block was thoroughly clean, and so I poured clean petrol through the orifices..  Inverted it and did it again.. Stood it on end and washed it out yet again.  Without any oil (or even oil residue or staining) facilitating "bits" sticking to the inside of the case, I'm satisfied that its clean and ready for reassembly.  That is after it sat out in the sunshine and light breeze to dry out. I have enough stink of petrol over me that I don't need to bring more into the house !

- - -   


^ speaks for itself, so I'll shut up (for a moment !)  :P


^ front roller bearing was liberally oiled before assembly. The bearing outer just sits in there against a circlip in a sleeve which is part of the crankcase.


^ look Mum.. no hands !


^ up ended for convenience of fitting the rear main bearing carrier. 


^ Likewise the rear main bearing was liberally oiled.  


^ being very careful not to catch that white-metal bearing on the hard edge of the crankshaft.  They damage easily and bits can chip off.



^ and there we are. The crankshaft is now in and the rear bearing carrier fitted and tightened evenly ..but with those nuts sitting on plain washers just for the moment.  


^ checking end float of the crankshaft at the rear main bearing. It's awkward to get in there with a feeler gauge but this 0.003" gauge is just fitting.  The spec says a minimum of 0.004"  but I learnt a while back that it's not so critical. This is because thermal expansion of the alumunium crankcase is more than that of the steel crankshaft ..so as the engine gets hot then this gap will increase.  In the meantime anything more than 0.002" will be sufficient for the thrust bearing's oil lubrication. So with 0.003" I'm happy not to pull it out ..just to scrape another one-thou off its white-metal arse.!

The bearing carrier's plain-washers were subsequently changed for split washers (I believe star washers were original ..but I hate those things), and the nuts were refitted with medium-strength Loctite.  Although there's no specification for their torque - I did these to 12 ft lb., as I like things to be evenly loaded.   

Well I think that'll do for today  ..so again I'll come back (possibly tomorrow)  with a further update..

Bidding you a good evening, on this gorgeously mild and sunny spring day.



Share this post

Link to post
Share on other sites


With the crankshaft and the rear end main bearing now refitted . . .


^ the components of the cam-chain tensioner blade and its bronze bush.


^ because the engine case limits fitting clearance, the blade is fitted first and then the bush (which is a sliding fit) is popped in.  Naturally, to get the blade out is the reverse whereby the bush is lifted out before the blade.. That's not intuitive, and clearly from some of the damage I've seen on other engines - some prior-owners simply didn't get it.!


The blade and its bush are retained on the pin with a sprung plate. One end sits directly onto the nut of the rear bearing carrier stud, and is fastened with another 5/16" nut.  Although it has its own lock washer - I still use Loctite on the thread. The other end of the plate has an elongated hole, as the plate sits astride the pin - so the spring bears on the blade and its bush.  Again beautifully simple, super reliable and easy to fit.


^ the valve timing is via this gear with sprocket (also referred to as a "half time gear"). It of course carries the timing chain which loops around a sprocket fitted onto the end of the overhead camshaft.  The gear has a bush within it, and this and the spindle need to be a nice sliding fit (not wobble). The spindle is pressure fed with engine-oil but they seem to wear more than most other parts on these otherwise unstressed engines.

New ' half-time-gear-spindle' and bush are available from Stewart Engineering, Poole, Dorset.  And for the best part of £75, for the pair - they are not cheap ..but a wobble free fit is required to avoid twist and therefore excessive wear in both the gear and chain, and more importantly - so the engine oil's pressure is not lost through / passed the spindle.  Both bush and spindle are an interference fit in their respective parts, and so need to be assembled using heat and a press (a vice will suffice as long as its jaws are square as it squeezes together ).   The spindle is drilled for the oil way and this needs to be carefully aligned before it is pushed in. Check the orientation after fitting by blowing through the hole to ensure it's clear.  The spindle should also be pushed in so there's minimal end float between the gear and its retaining thrust washer.


^ As stated above, there should be only a tiny amount of end float of this gear on it's spindle.  Measuring this., I found it to be 0.015" ..which is too much to retain the lubricating oil.  However., with a confident tap squarely on the end of the spindle - it went in ..and this end float is now 0.002 - 03".


^ The cam-chain has to be assembled onto the sprocket and fed through the engine case as the timing gear is fitted. The original timing chains were endless, but most replacement chains have a link, and this link ought to be pointing in the direction of rotation so its tail-ends cannot snag. Please see small red arrow next to the chain link in the photo above (that link is also seen below).


^ The timing cover (which I'll be fitting later) is secured by ten screws, and the top one (which I'm seen holding) is extra long - so it protrudes into the cam-chain chimney. This thoughtfully little detail prevents the chain from slipping down and getting tangled.  You might also note that I've temporarily wired a couple of the chain links together, so even the top loop of chain cannot drop passed that screw as I turn the block upright.

Small details but a little forethought helps subsequent assembly.

More to come later. Happy Easter - Pete.


Share this post

Link to post
Share on other sites

. Ok, it's time to get on with things.. the shut-in of coronavirus is leading me to become complacent with my days  ..and I just know I'm going to be really frustrated if in a few months time I haven't achieved much.  So...


^ having noted which way around things go.. with the recesses for the valves in the pistons facing the right hand side of the engine and the cylinder number ( '2' in this case) stamping on the conrod also facing right. 


^ I feel a little extra cylinder lubrication helps during those first few moments when a rebuilt engine is first started, so I add a tablespoon of engine oil to the hollow gudgeon pin. If you're wondering - I align the split end of oil scraper rings with the gudgeon pin (one front, one rear facing) and the compression rings at about 15 degrees off the crank's axis (again one front, one rear facing).


^ just checking the conrods have landed squarely to the crank, the bolts are in place and I add a drop more oil before fitting the caps. 

.   P1340326s.jpg.4118b47f121d7ef762076f656f3b82ec.jpg

^  checking again that the stamped numbers on the con-rods and caps are correctly orientated and also that the crank and pistons are relative free rotating, throughout a full rotation.


^ the big end bolts on these engines are tightened only to 25 to 28 ft-lb and then split pins are fitted through their castle nut.  I tighten in stages to just 25 ft-lb and check their alignment with a length of wire (which at this stage is easier than trying to reach in to see if the split pin will fit).  A keen eye will have spotted that I've marked the ends of each big-end bolt with a line of Tippex (white typist's paint is very quick drying) to indicate the hole's orientation. 

With castle nuts ; the alignment of their slot to the hole (through the bolt) is a matter of how far the nut turns down the thread ..at that specific torque.  Unless the bolt and the nut have gone back in exactly the same hole as they came out of then most likely they wont align.  However before you start filing down the face of the nut, try swapping the misaligned nuts around.  By doing so, on this particular engine, I found only one nut's slot didn't align to the hole through the bolt, at the prescribed torque setting.

As I'm rebuilding two engines here, I'll not yet file the face of that one nut down - until I've caught up to this stage of reassembly with the other engine ..and tried the alignment of their nuts on those con-rod bolts.  I might find that by swapping misaligned nuts from one engine to the other I find a match.  

I'm sure you are asking yourself  'didn't he use new big end bolts and nuts ?'  and the answer is no.  This is not a recommendation it is an just an economy I make ..a risk I take with my own engine. 

It is an interesting question., how far you go with a vehicle that's 50, 60 or 70 years old ? Do your replace every stressed nut and bolt in the engine, suspension, brakes, frame ? After all - they are all stressed (otherwise they wouldn't be there) ..but then many are more critical than others.  If not every one, then which do you replace ?  How much do you spend ?  I guess, he who pays the money must make their own decision according to the depth of pocket -v- the potential risk of some serious damage.  However a compromise might be to replace the bolts and save money on the nuts (which I've personally never heard of breaking or stripping).

The cost of a set of bolts is another £120 + the nuts at £57.  And I'm rebuilding two engines (of my own bikes).  £350 is not a king's ransom in the big picture of things, but as I ask - where do you stop ?  If your insurance premium went up by £350 what would you say ?  But this is a one off cost you answer ..but next you work on the brakes, and then the forks, and then . . . 

The argument to change them all is compelling . .

The torque setting of these bolts low and the stresses in these engines is also low, but you never know what they were tightened to by a prior owner.  I do check the torque as I dismantle engines, but then I didn't happen to dismantle this one. And I have had personal experience of the head of one of these bolts coming off ..on a running bike I'd bought (previously restored by a chap in the vintage bike club).  As it happens I felt the engine's vibration and stopped. Having eliminated other possible causes I investigated it by dropping the sump and found the offending part. No damage was done.  Perhaps I was just very lucky, or perhaps I'm attuned and sensitive to these engines and so the risk is less for me than for the average rider. That's not a boast - it's simply a question. 

There have been many times when I've ridden these bikes fast and then such a breakage may have been catastrophic.  But then I have bought a lot of second hand cars and bikes in my lifetime, and ridden and driven a whole lot more ..and a great many of those had been rebuilt by someone other than a factory trained mechanic.  Am I reckless to ride or drive anything that's not been professionally restored at a cost of four times the value of the vehicle ?  Would you be reckless to drive on the same roads as people who rebuilt parts or have nut n' bolt restored their own vehicle ?  Should all vehicles over ten years old (or whatever) be scrapped because something might fail ?

I'll leave it with you. B)



Share this post

Link to post
Share on other sites



^ the government told us to stay inside !

Anyway it was time to play catch up with the other engine..  I'll try not to bore you with repeating the same as I've posted before but here are a few differences . . .

Staring off with fitting the front main bearing to the crankshaft. .


^ This is old one which was only pulled for access and removal of the core plug to the crankshaft's centrifugal oil-filter / gallery. With that now refitted and this bearing appearing to be fine - I'll refit it.


^ The bearing is an interference fit on the end of the crankshaft, so with that ready positioned to take it - the bearing was soaked in boiling water (so as to have it thermally expand in diameter) before being dropped on.


^ To avoid hitting (or mis-hitting !) the actually bearing race with a hammer,  I used the outer journal of a old steering head-race bearing as a drift ..to tap the main bearing all the way onto crankshaft.  I have a drawer with an assortment of bits of metal like this head-racing bearing ..kept for any such tasks.  And it's surprising how often they are useful.

P1340346s.thumb.jpg.6bd030963d267e55d4aa0ef3adf45fba.jpg .

^ The outer journal / housing of the main bearing needs to go into the end of the crankcase until it's hard up against the circlip.  It's an interference fit and I don't have a large enough oven to put the crankcase into ..to heat it up.   And I know from previous experience that the aluminium case is too excellent a heat sink to heat up with my blow torch and so I had to just press the bearing in.  Of course it has to go in very squarely. 

I started the process by loosely placing the housing in place, fitting the crankshaft into that and then placing the rear bearing carrier to align with its studs. That meant that everything would be in line. And then with a block of wood to protect the crankshaft from shock impact - I used a hammer on that block (held over the rear end of the crankshaft) to knock down.  I didn't do very hard ..because I didn't want the impact force to damage the cage which holds the roller bearings.  Still it was just enough to start the front bearing's housing squarely into the crankcase.

The temptation is to then remove the crankshaft and use a block of wood, through the crankcase, to knock the bearing in.  In practice the bearing then just tilts. It's simply too tight a fit to go in squarely, so I needed a press.  I don't have a press but could work from the outside if I used a puller.  In searching for a couple of plates to put a big bolt through ..I looked in said drawer where I keep oddments of metal and also my gear / bearing / sprocket pullers. By combining the parts from two I reckoned I could make an appropriate tool. 


^ the three legged puller is something my brother made at school  (he went to a grammar school where they did things like metalwork !). As a puller it's actually pretty useless and I've long since replaced it,  but it never got thrown away because sometimes one puller can be made to fit and work where another just wont.  The cyan coloured four legged puller (above) is actually for the diaphragm clutch on my Norton.   Anyways, by using the disc and screw handle from the one and the legs from the clutch puller - I had myself what looks to be a perfectly sized tool to draw the main bearing's housing into the crankcase.  

It didn't want to go easily but by cranking the handle and then striking the screw end of the puller, or its draw plate .. little by little it did go in. 


^ Subsequently, with the crankshaft dropped into place and its rear bearing carrier tightened - I could check this crankshaft's end float. I'd had a rear main bearing made in bronze, which cost no more than buying a white metal one from Stewart engineering (which I'd done previously on another bike of mine), but this one's end float measured at 0.007,5 - 8"  (spec says it should be 0.004" max) so something needed to be shimmed.

The recommended way is to push the rear main bearing out of its carrier, and to make and fit a shim behind its thrust face flange.  Instead I did the shimming at the forward bearing. . 


^ raw materials to make a shim from. The steel Boddingtons beer can is 0.003" thick ..which would have been good for my needs,  but I didn't have any more of that can not any others in or around the house, and nor did my neighbours. The shoe polish lid was 0.010" thick steel, so too thick.  And I searched around to see if an aerosol or something else might be used ..but nope I couldn't find anything.  The lemonade can, courtesy of a neighbour, is made in aluminium and is 0.006,5" thick  ..so again little too thick.  However being in aluminium I hoped it might squeeze thinner (like an aluminum or copper gasket does), so I tried it.


^ the thin aluminium cuts easily with kitchen scissors.


^ with the bearing housing tapped in just a little, and the circlip temporarily removed, I could fit the shim. The bearing housing was pulled hard against shim against the circlip, which locks it in place.

Once the crank and rear bearing housing were reassembled - I felt they were too tight, so I pulled it all out again, rubbed the face of the shim down with fine emery paper, and tried again.  It was just a little better but imo still not enough, so then I redressed the face of thrust bearing ..now all I needed was a thousands of an inch.!   With that done I was content that there was a couple of thou end-float ..which is sufficient for its lubrication. And as I've said previously - the gap gets more as the crankcase thermally expands.

The oil pump was checked and its own end float minimized (as discussed in a previous post), the oil pressure control valve's ball & spring were replaced for new, and the oil ways within the bearing carrier checked for their being clear.  This timing gear's spindle was blocked when I first tried to blow through it, but then it cleared. I wonder if there was a bit of tissue paper within ?  Whatever it was, I'm very glad to have spotted it, because very possibly it wouldn't have cleared once the timing gear was fitted, and so would have starved that bush of oil).  


^ the timing gear's bush was too long and standing proud of the face, by 0.018".  It is meant to be flat against the thrust washer because the small surface area at the end of the bush would soon wear down, and then the end float would be large so oil pressure would more easily be lost. 

I used a power file to take most of its protrusion down and then scraped it with a craft-knife blade until perfectly flat and level with the surface. Once cleaned, refitted with the thrust washer and circlip - the pin was tapped further into the bearing carrier so its end float was minimal (ideally 0.0015 - 2" for oil).   Job done.    

That's it, after pulling it all apart again ..to liberally lubricate each of the bearings - the crankshaft is again in place with the rear bearing carrier, tensioner blade, timing wheel and chain.

Have a good weekend,


Share this post

Link to post
Share on other sites

Good Morning all, 

I don't know why but I've been really demotivated to get on with these rebuilds (my state of mind is a fickle thing !) so again ..just a little update. . 


^ Catching with the second engine by fitting the pistons with their rods.  I ought to invest in a decent piston-ring compressor so this task would be easier ..but as I so rarely rebuild engines - it seems as if that would be just another tool taking up space in a drawer for years until it corrodes, gets biffed and bent or whatever.  In the meantime I tried a slightly different approach to fitting these ..insomuch as I fitted the two oil scraper rings and then fitted the piston into the bore, and only then I fitted the compression rings one at a time and inserted those. For the way I do things I found it easier.

P1340387s.thumb.jpg.c1aeeca52e57962cb3cf594cc37ff08e.jpg .

^ I made a mistake in not checking this cylinder head sat down on the block before I reassembled the crank and pistons.  When I did try it I found it stopped here (above).  This is a common fault on these engines and why so very many of them have broken cooling fins.  The cause is that the cylinder heads are tightened so much - their stud's nuts pull into aluminium. The aluminium around the bottom of the hole is crushed and distorted ..and squeezes sideways into the holes, until it grips tightly around the studs. 

Of course, when trying to lift the head off - that displaced aluminium catches even more on the stud's thread ..making the task very difficult indeed.  The way around this is to place wide load-bearing packing pieces under the nuts, between those and the next fin down (you can see the gap in the fins above where the nuts will be fitted)  ..and then to systematically unwind the nuts against that packing to jack the head up.  It does take a fair amount of time to make up suitable packing pieces and then to pragmatically unwind each of the nuts ..in diagonal order, so the head lifts up squarely.  However, when it is done 1/8th turn of every nut in sequence - the technique is successful and no fins are broken. 

Is this is a design fault ?   No, it's a consequence of poorly designed and incorrectly made after-market copper gaskets. . .


^ The top gasket is a composite of copper foil on either side of a fibrous (asbestos substitute) packing.  In practice these  gasket seal where the copper foil is a wrapped back over the insides of the holes (those for the combustion chambers, the timing chain, and the oil way drilling).  For that first 1/8"  the amount of copper foil is half as much again ..and so it's like a lip seal around those apertures.  And because the foil over fibre is very thin - then very little pressure is needed to form the gas and oil-tight seal.   The nuisance with these gaskets is that they compress more ..and so the cylinder head nuts need to be re-tightened more often (during running-in) than when using a solid copper gasket.  If they are not re-tightened - then the combustion gasses will soon start to blow passed it,  and if not addressed immediately ..because of the heat involved, the thin foil it will melt and the gasket will fail completely.

The lower gasket (shown above) is of solid copper (please ignore the black lines and writing for the moment, they are mine).   As you can see it is shaped to the very same pattern as the composite gasket.  Gasket sealing pressure might be thought in terms of p.s.i.  ..that is pounds per square inch  ..and the "per per square inch" is a direct reference to the surface area of the gasket that is being pressed to seal.  In these two case ; the composite gasket requires the studs to pull the cylinder head down just enough to compress 1/8" edge of a thin foil copper against its fibrous core,  whereas the solid gasket requires those same studs to try and compress the full 3/4" width of solid material.

If they were both in foil then that might be six times more surface area, but the fact that the latter is solid metal - then many times as much pressure is needed to compact it.  I don't know how many times but I do know (from frustrating experience) that unless the head and block have just been skimmed - it can be very difficult to get these composite gaskets to seal properly. 

The situation is made many times worse by the parts supplier who does not specify an appropriate ductility / softness of solid copper.  This can be corrected by annealing the metal again (and then cleaning its surface oxidization off).  Annealing is a process whereby the metal is heated up until ruby red - whereby its molecules all spread out to being in an uncompressed / unstressed state. These stay 'relaxed' as the metal cools again.  However, as soon as that metal is worked (..as was the metal when it was rolled into a flat sheet before being cut into the gasket shape) then it is compressed and goes very hard. 


^  I had these two gaskets re-annealed by a garage mechanic friend of mine on the day of the corona-virus shut down. I didn't have the time to get across town to the engineering company I've used before, and I knew my butane blow-torch wasn't hot enough - it needed an oxy-acetylene torch.  Unfortunately, my friend had no experience of doing this and destroyed one.


^ too tight and too hot a flame from the blow torch melts the metal,  and as a molten metal it pools and wrinkles.  That's now scrap and £61 to replace it.  The flame needs to be broad and constantly moved / wafted back n' forth to see the colour of the metal as it gets hot.  Firstly it goes maroon in colour, and then ruby red, and at its hottest a bright cheery red.  Ruby red is just fine, no hotter.  This needs to be done evenly all around the gasket, bearing in mind the narrow sections of the gasket (like around the timing chain tunnel and around the holes) need less heat than the wide areas (which dissipate the heat away).  Copper annealing does not need to be quenched in water to cool it.  It's fine just to be put aside and allowed to cool in the air. 

What were the marks / lines on the previous photo ?  Well, this is something that I've thought to do before but never got around to it.  But I want to try to reduce the surface area of the solid gasket.  So, where it was very wide, I've market 3/8" outwards from the combustion chamber holes, and then radius those lines to the studs.  Using the now scrap gasket to play around with I re-cut the shape . . 


^ work-in-progress looks terrible but getting in with a Dremel's cutting disk doesn't go around corners very well.  Cutting half way through the solid gasket and then snipping into that I was able to break out the big pieces.  Thereafter I used a 4" angle grinder, a hand file, and the Dremel's drum sander to finish my reshaping and to make everything smooth. . .


^ 3/8" wide where it was 3/4" wide before. I did not alter those areas which were already narrower.  I'm pleased with its reshape. 


^ the revised gasket on the left  in comparison to the 'standard' after market solid copper gasket.  

I haven't tried to calculate the surface area of these gaskets, but I did the next best thing and weighed it before and after cutting. The scrap one was 162g and after being trimmed it is now 141.7g  so it's 20.3g lighter.  And that's 12.5%.  As the thickness hasn't been altered then that same percentage is off its surface area.  So as modified - it is seven eighth what it was.  Or put another way  (re. pounds per square inch) the studs need only be tightened to 7/8th the torque they would have been to achieve the same degree of sealing compression. 

I think that's very worthwhile, so I'll keep the first one as a template.  Oddly (or otherwise) the modified one even looks right .!

I'll leave it with you, as I now go out to the garage to modify the other (good) one.

Cheers, Pete.

Share this post

Link to post
Share on other sites

.. filling in a few tasks . . .


^ following on from the cylinder head not sitting down, because the bottoms of its stud holes had closed up from their being done up overly tight...  I sellotaped over the cylinders and the oil way drilling (smaller hole on the right hand side of photo) before drilling the stud holes out.  I really did not want swarf inside the engine at this stage.  

- - -

 Next job was to finish up in the bottom end . . 


^ having sorted nuts out so that, when tightened to 25 ft lb., their castellated heads to would align with the holes through the big-end bolts (done in pairs and appropriately ticked / marked with the felt pen so I know where I've got when working on two engines) I then fitted the spit pins.  On these engines I use 1.8mm dia steel pins and cut them to the 3/4" length I want.  Don't know why but 1.4mm pins seem a more common size but they rattle around in these holes (not good because rattling around means wear, which in turn means breaking). 


^ Close up of how I bend my split pins.  The pin is fitted and its looped head is pushed tight into the hole (I use a screwdriver blade to lever it in). Only then is the longer end of the split pin is folded back over the end of the bolt and the short tail of the pin is pushed downwards and pinched flat to the side of the nut.  These nuts have a shoulder on them (ie., a built in washer) and so the length of split pin is pretty critical to achieve a good tight fit. If the split pin is too long then it doesn't sit flat and then rattles around as the con-rod reciprocates.  If the pin is too short then it's a right pest to get in and to fold both up and down.    Tip : when cutting your own to length - cut across the split so that the metal is drawn inwards. If you cut flat to the split - then the metal tends to flare out wider ..which then makes fitting them through the holes more of a pain. 

Job done, and its time to move on . .

- - -

The sump can be fitted now but if you drop a cylinder head nut or its washer down inside ..then you might wish you hadn't.  I fitted this engine's ..but only using gasket cement on one side of each of the three gaskets (two gaskets are normal for these engines, but three are used when the sump extension is fitted).  I fitted all the nuts and washers, as will be used during the final assembly, but torqued them systematically (diagonal sequence) to just 4 ft.lb.  This brings those gaskets to a light but even pressure ..so as to not squeeze all the gasket-goo out.  It can can be curing while I get on with other tasks. 

- - -

Next . .


^ crankshaft drive gear for the valve timing gear and oil pump.  Note the woodruff key is already fitted into place in the crankshaft (..the second key slot is for the flywheel) and the two dots on the (large) timing gear are aligned to that woodruff key, as these are the valve timing marks.  


^ not wishing to see that woodruff key disappear into the crankcase - I've bunged the obvious holes through the bearing carrier with rags. The screwdriver is just loosely placed but it's enough to prevent that key from being pulled out as the gear is fitted.   It does need to be checked several times over during fitting ..as the little blighty does like to move. 

You'll note that I've used my felt pen again to mark the drive gear's tooth which aligns with the woodruff key.  That may seem unnecessary from this photo, but I use a piece of tube over the crankshaft as a drift - to tap the gear down into place ..and then I can't see the woodruff key slots.!   Of course this has to be done with care so that its teeth align suitably with those on the timing gear and oil pump.

Only because I had the timing wheel on (to adjust its end float on the spindle) did I fit the crankshaft gear now.  Of course, when fitting the pistons and con-rods it is easier to turn the crank without the chain getting in a twist,  but on the other engine I'll revert to doing things my usual way ..and fit this gear onto the crankshaft before I fit the timing wheel with its chain.


^ all done,  but I'll not fit the cover over this until I put the cylinder head on and do the valve timing at the camshaft sprocket.   By the way ; the woodruff's slot is cut to the same plane as the crankshaft, so with this pointing straight upwards the crank is at top dead centre.

- - -

And the following reflects a little tidbit of design evolution ..


^ the engine to the right is the older engine ..1948 or 49 judging by its number, and you can see (red arrow) how the drillings for the cylinder head studs are off centre to the engine block.  The later engine was modified and is drilled straight. .


^ this engine's has this extra flat cast onto it.  it serves no other purpose so I presume it is to align the cylinder head stud's drilling jig to the block.

I like curiosities like that :)

- - -

And finally for this post . .


^ this engine block has +0.030" pistons and has recently had a replacement cylinder liner.  At that time its gasket face was skimmed ..but I don't know by how much, nor do I know if it had been done previously (once or twice), nor do I know if the gasket face on the cylinder head had previously been skimmed as well.   

Comparing the two engines ;  the piston crown to gasket face on this engine measures 0.009" ..and on the younger engine with standard sized pistons it measures 0.030" (so over 1/2mm difference on an engine with 63.5mm stroke).  There's nothing I can do about it ..but I will fit the thicker (0.062" thk) / solid head gasket to this engine and the skinnier composite gasket to the newer one. That (composite) gasket presently measures at 0.050" thick, so it's only 0.012" difference, but it is very much more compressible when torqued down a few times, whereas the solid one will hardly compact at all.

That's it for tonight..  I bid you a good evening.




Share this post

Link to post
Share on other sites

Ok., here we go again..


On your marks..  get ready..  set..  go  :D

^ The solid copper gasket was re-shaped to being a closer match to the stud pattern with less psi area.  This one took a little less than an hour-and-a-half to modify and by tightening my redesign up just a little more - it is now 14% less surface area than it was  ..as importantly perhaps is that it is a similar width all the way around. I'm hoping this will translate to being a more even pressure when tightened down. 

I also eased and chamfered the stud's holes, so the gasket doesn't snag on those threads and because if the copper is expected to squeeze down - then it has to go sideways, which it cannot do if the holes are already tight to the studs). 


^ I reuse but cleaned up the nuts and also ground / flattened one end of them. As standard they are quite rounded ..which of course worsens their tendency  to pull into the aluminium cylinder head.  Thick washers are always used but they always bow in - so on these engines I'll try double washers under each nut. The larger diameter ones were too tight for the four studs adjacent to the cylinders so I've cut a flat on those.  All together they'll be a pain to align and fit ..but I hope they will help because if the washers don't pull in - then less damage will be done and the head studs ought not need re-tightening so often as they bed in.   win win !


^ I use Wellseal joining paste / gasket goo. Whether this or any other gasket goo works in this situation (cylinder head temperatures, cycles of thermal expansion and contraction, head being tight and then needing torqueing down again, etc.) is in my mind questionable, but it is recommended ..and I can't see it does any harm.  You'll note I only apply it where it actually seals around the combustion chamber, oil drilling and cam-chain chimney.  There's absolutely no purpose in spreading it around the stud's holes ..because they cannot leak anything, not even those in the cam-chain chimney.


^ The nuts are first placed into the block and the washers I'm using carefully rested on top of those, before the cylinder head is lowered down. Inevitably it rests on one or more washer, but by taking the weight off they can be slid into place.  The nuts then need to be lifted up to the stud's threads. I use one of my old feeler-gauge blades to do that. Then it's just a matter of winding them on. This is where you're glad you cleaned all the threads so they go on easily.  

Note the black plate under the front (right hand side of photo) which has two holes in it.  This is needed to transfer the whole weight of the engine to the front engine mount, which fastens through that forward boss.   Without this plate the aluminium is stretched / pulled upwards and can crack the casting. That crack goes inwards to the cylinder and leaks oil.  To repair it ; everything needs to be dismantled and the front cylinder liner removed, so the aluminium casting can be welded from the inside.  Even then it's not easy to weld an aluminium casting, less so because of the limited access, and less so again because that crack has engine oil in it.  Much better to avoid all that hassle (and cost) by remembering to fit that plate.  I use a 3/8" diameter Tommy bar (seen in the last photo) to keep the plate from turning / in line with the engine mount hole, as I do that cylinder head nut up tighter.   


^ at the back of the engine there's a 5/16" nut on either side (externally) and then a 3/8" rear cylinder head stud and a 5/16 chimney clamp ..which each need a washer and their respective nuts ..taking extreme care not to drop those into the crankcase !  When the engine is in the bike you can barely see into this space (..the battery's case is in the way) and then the cam-chain is in there too, so the inner nut tend to get missed / forgotten when a stranger to these engines tries to prise the head off ..with levers and using big screwdrivers as a chisel !  And again it tends to be ignored by owners when torquing the cylinder head down during its running in.  Big surprise the head warps and oil leaks out.  It's not difficult but one does need to be conscientious. 

As you can see, using a torque wrench and socket to tighten the cylinder head nuts is impossible, you cannot even get a ring spanner on them, so a good quality (because these need nuts to be very tight) open ended spanner is necessary. The eight 3/8" nuts take a 5/16" Whitworth spanner and the three 5/16" nuts is a 1/4" Whitworth.


Presently this cylinder head is only loosely pinched down. ie. I used a 7" long spanner but as evenly as I could (all 11 nuts) only at a modest pressure.  The Wellseal has an opportunity to set as I get on with other tasks. 


    ^ that's it for now.. I have a long engine again.   i think it's very elegant.

Happy Friday,





Share this post

Link to post
Share on other sites

With the cylinder head now on, albeit not torqued down properly tight, it's opportune to set the valve timing. .

Firstly, and necessary for setting the valve's timing, the camshaft needed rotated so the dowel hole in its end was upwards.  I had assembled this camshaft 180 degrees out, so I now had to loosely fit the chain's sprocket ..so that I might grip the cam to turn it around.  Important - Before trying turning a camshaft (which in turn lifts / opens the valves) ensure the pistons are not at the top of the cylinder bore. The timing mark on the flywheel will reveal this,  otherwise very gently probing the piston crown with a screwdriver in through a spark-plug hole will. 

I had set the chain tensioner right the way in (..to help stop the chain from tumbling down the chimney) so this was slackened all the way off.  And then the timing-chain was hooked with a piece of wire and pulled all the way up into the cylinder head.  It's quite a tight fit in there and takes a bit of wiggling to get the links passed the tightest constriction ..but it does come up without brut force.  The cable wrap I had tied through its links (again to prevent it from tumbling down) was removed ready to fit the cam-chain's top sprocket. 

The space in the chimney is also too tight to fit this sprocket passed the chain, unless the chain is first looped over the protruding end of the camshaft. That 3/16" is sufficient to slip the sprocket passed it. 


^ A screwdriver slipped in through the hole (where the distributor will soon be fitted) and through the sprocket is used to stop it dropping down into the chimney.  Held up, but lowered on the screwdriver, the chain can be fitted over the sprocket.   Note from the photo the dowel pin is upwards as the chain is fitted.

. P1340495as.thumb.jpg.e101044650a6c92697168ed0e221ba8b.jpg

^ As I loosely put the sprocket's bolt in, I only then noted the dowel pin was not flush to the face. It was but is being pushed out. I really ought to have checked and done this beforehand. I am getting absent minded in my old age. :blink:


^  in brief..   (Left) the dowel pin as it was.  I tapped this in until it was about 1/16" below the face and used an angle grinder to cut a shallow grove. I welded over that and then ground the weld back to being flush.  Job done,  now to put it back in the engine.


The handbook descriptions and illustrations are not very clear on setting the valve timing, so here's my take on it. . .


^  1.  Bottom left    I marked the tooth which aligns with the dowel pin with a touch of white paint ..because it's easier to see (Nb., this sprocket looks a bit skewed because it is only very loosely fitted). Hardly noticeable but I also dabbed a spot of paint on the protruding end of the camshaft to indicate the orientation of the dowel's hole.  But what's important to note is that marked sprocket tooth is (correctly)  inbetween  the  chain's  outside  link  plates.

^  2.  Top Left   Looking from the rear ;  the hole  for the distributor's dowel can be seen vertically under the sprocket's bolt.  With the camshaft timing correctly set - the chain's link (seen at the top)  adjacent to the paint-marked tooth is horizontal   ie.,  level with the rocker cover gasket face.   

^  3.  Right photo   this flywheel was temporarily and only loosely refitted onto the crankshaft ..with its woodruff key fitted. The white paint on the rim of the flywheel (arrowed) is orientated to that woodruff key  ..and as you can see it corresponds to one of the clutch-plate studs.  Because the timing-gear marks had already been set to align with the crankshaft drive-gear's woodruff key - their vertical alignment means the crank and pistons are at t.d.c. (top dead centre).  NB. The gearbox bell housing has an inspection window so, if this job is done with the engine and gearbox together (perhaps just the cylinder head is removed for a decoke or valve rework) - then the t.d.c. mark on the flywheel (..&/or that clutch stud) might be seen through it.

For the valve timing to be correct - Each of these alignments are necessary.

If any are not - then the timing is incorrect.  For example ;  If the white painted tooth is inbetween Inner link plates then the timing is incorrect.  The sprocket then needs to be released and lowered (on a screwdriver) so the chain can be hooked (with the piece of wire) and lifted over the sprocket's teeth. The marked sprocket tooth must be inbetween outside link plates, and those plates have to be level with the top, while the flywheel's mark is vertical.

Conversely, if the sprocket's painted tooth (aligned to the camshaft dowel) is inbetween outside link plates, but those are not sitting horizontal / level, as the flywheel indicates the engine is at t.d.c.  - then the valve timing is set to the wrong cylinder ..and although the engine may start, it will run very poorly.  To rectify this - the sprocket needs to be released and lowered onto the screwdriver, and then the crankshaft needs to be turned a single revolution   ie., until its paint mark is back to vertical.  The top chain sprocket will then be found to have tuned 180 degrees ..so is in effect upside down.  It must be lowered enough for the chain to be hooked (with the piece of wire) and lifted over the sprocket's teeth. 

The crankshaft and the chain are not being turned, but each time you do this the sprocket will turn a tooth at a time, and so the painted tooth will soon come back up to the top.  Again it has to be inbetween outside chain-link plates, and be at the very top, and those plates have to be level with the top, while the flywheel mark is vertical.  Then you have the correct valve timing. B)


^ After double checking and so was sure the valve timing was correct,  I properly fitted the sprocket onto the camshaft (pushing the dowel right the way in), cleaned the bolt's thread and applied Loctite (2400), and tightened the nut to 25 ft.lb.  This necessitated preventing the crankshaft from turning - for which I used a piece of softwood as a counter to the leverage.

Valve timing / cam-chain stuff - Done. :)

It's time to take that flywheel off again and to seal up the back of the engine. 

More later. Have a good day. Pete.

Share this post

Link to post
Share on other sites

a little more from yesterday .

The task was simple enough, to clean up the closing plate at the back of the engine and to fit it. It started off well enough . .


^ The closing plate on these engines is a shallow steel pressing which contains the rear crankshaft oil seal.  The original seal (part # W28721231R4) is likewise very shallow (1/4") and has a steel outer case.  Surface rust and staining both inside and outside these plates is usual.



^ the closing plate sits on a soft cork gasket and there are ten 1/4" set screws with equally as tiny split lock washers to fasten it.  Because the fastenings are so localised - they pull / bend the relatively thin metal in around their holes. So then the gasket face is no longer flat and need to be redressed (flattened and made smooth). Getting in with panel beating dolly is easy along the straight edges but less so around the curves.

.P1340516s.jpg.3ea1459c987a4167c792ae52efa21057.jpg   P1340518s.thumb.jpg.3a580e3ec31746b2208e677c45d13719.jpg

^ Redressed, clean up and painted.  I've used zinc / cold galvanising paint + HT silver + petrol proof lacquer.  I don't like rust on nor in my old motorcycles - but its finish is not critical because it is out of sight behind the clutch. 

. P1340417s.jpg.2a3277a56708a9ec802af76842a74ab3.jpg

^ The replacement rear crankshaft oil seals are rubber coated and deeper.  That's like putting a soft rubber bung only half in a hole, with a bulge of rubber on the outside wanting to make it pop out again.  It's happened twice to me  ..on running bikes.  which on both occasion meant taking the engine & gearbox out again, to remove the clutch & flywheel to get to it  ..not something which made me have 'nice' day.  The first time I naturally thought I'd got it wrong. Second time around I realised the after-market seal was of the wrong specification. 


^ But., as that is the replacement part available, then  IT  MUST  BE  GLUED  IN.   I clean my paint off the inside flange and use a thin smear of Araldite Rapid  ..which worked previously. 

. P1340419s.jpg.69b531e19547de2aadb521435fd9274f.jpg

^ The engine's rear plate with the seal being glued in.  It needs to be held in place while that glue sets, and the cylinder head happened to be a suitably heavy lump to keep it pushed in.


^ ten screws with washers are used for each cover but here I'm preparing for two engines.  I use stainless penny washers and cut a flat on one side and then bend the other side up by 15 - 20 degrees.  It's a like a mini production line when you're doing 20 of them.  Tip ; to start the cut - a little notch (with an angle grinder) helps prevent the hacksaw blade from slipping sideways.


^ the new specially shaped penny washers seen loosely placed.  Clearly these distribute the clamping force of the screws more broadly than the tiny (original) lock washers.  

. P1340535s.thumb.jpg.6498b2e41e389919fece86a68450f624.jpg

^ The oil-thrower disc is fitted onto the crankshaft first, and an O-ring is used between that and flywheel - to keep it from rattling around. The seal works against the flywheel.  I've used Wellseal jointing compound on just one side of the cork gasket ..which glues it to the inside face of the timing cover. The other side of the gasket is fitted dry.  While that gasket goo sets the screws have each been tightened only loosely (setting 9 of 16 on my cordless screwdriver's ratchet)

That's it for now  ..almost


^   I'll not dwell on my immediate feelings toward the 'professional'  who had this engine case blast cleaned with fine grit / sand. :evil:     Aside from what was poked with a small screwdriver and then sucked out by the vacuum cleaner, the photo shows grit from just a few of these screw holes.  I guess my jet washing the block just made the sand wet !   I had to remove the cover again (the screws wouldn't go in) and I exaggerate not when I say that it then took another two hours to clean the grit out of those threaded holes. ! :angry:   I cut the set-screw (1/4"  Whitworth thread into the aluminium)  up its length with a hacksaw to use as a tap to clean the threads out.

Sand and fine grit is so very much the wrong stuff to use for cleaning engine / gearbox / final drive cases / etc.  as it gets in everywhere ..and it is an absolute bitch to get every single grain out again.  In this particular instance, despite my having jet-washed this casting and then also flushing out its inside with clean petrol - I had missed checking these threaded holes.   I've worked dozens of these engines and I've never before had any issue with fitting this cover  ..But then when I take a casting for cleaning - they know better than to use sand or fine grit,  and I make sure all the studs are still in place and all the screw holes have a fastening in them (..which also get cleaned ..which saves me hours).  Similarly bearing surfaces and the oil drillings are taped over (double layer of gaffer tape works well).

I've scrapped the cylinder head this professional also had cleaned, so this crankcase is the only blasted part I'm now using, but my finding this  ..at this late stage in reassembly is a worry.  I have to place my hope in the modern (and very fine) disposable oil-filter I'm using.  But still I'm inclined to use a flushing engine oil and to change that after a very short period of running. 

It's done now ..so time to put such things behind us and move on.

Bidding you all a good weekend, Pete.  B)

Share this post

Link to post
Share on other sites

Good morning. It's been a couple of weeks since I last posted so here's a quick catch up from where we were last - closing the rear of the  engine. .

With not having inadvertently dropped any nut or washer inside the engine as I reassembled the timing gear and/or fitted the cylinder head, I closed up the bottom of the engine. The following shows my own conversion to a modern(ish) oil filter. .


^ As previously discussed < here >  I am using a sump extension to give the engine more engine oil capacity, I have extended the oil pick up pipe to the lower level so there is much lesser risk of the oil pump sucking air,  and I'm replacing the gauze wire mesh 'filter' to using a very much finer disposable paper element oil filter (HOF306).  The above shows it configuration during final assembly, and the dark grey coloured 'O' sitting on the steel baffle (between the crankcase and the sump) is a magnet to collect particles of wear (eg., running-in of the honing of the barrels). Likewise the oil drain plug (which I'm seen holding) also has a very strong magnet set inside it.  

All the stud and nut threads are clean and the gaskets faces have all been redressed to be clean, smooth and free of distortion, so the bottom-end could be closed up. .


I've replaced the original washers with fibre ones.  And because there are so many fastenings to this little sump - the nuts don't need to be very tight.  I am however very particular in tightening the sump down both progressively and in a diagonal sequence.  Final tightness of these was just 8 ft.lb. with no Loctite.  Once the engine is run up and heat-cycled a couple of times - these gaskets will compress slightly so the nuts will need to be re-tightened.  In my experience it is better to do this a few times during running in, than to over-tighten them in the hope of never having to check them again. That doesn't work when there are three cardboard gaskets being compressed.  A Japanese engine without gaskets and with stretch bolts might work that way ..but this is British 1940's - which has lasted for seven decades and works exceedingly well .. but only when assembled with empathy in the first place.

- - -

The next item up.. was the cam-chain tensioner.  .


^ the robustly built item seen here screwed into the side of the block is simply a spring plunger with adjustment.  The double springs inside is to keep a little tension on the back face of the chain tensioner blade.  I use PTFE tape around this tensioner's large screw thread and wind it in.  The inside (sealing) face is conical so doesn't need a gasket, o-ring, or fibre washer.  The fibre washer you see there is for the aluminium cover (which I'm seen offering up).  

I've swapped-out the cover's usual set screws for countersunk stainless steel ones.  The originals sit on tiny fibre washers but I'm trying these countersunk ones without.  Instead relying on their conical shape to give me a seal.  In due course we'll see whether it works. 


^ Only out of perverse and passing interest,  above compares the rounded shape of later chain-tensioner cover with the sharply defined one of this earlier engine.  You can also see the cheese head type of set-screw I replaced with the countersunk one on this engine.

Moving on, or perhaps I should say moving out ..


^ It's not terribly heavy so I could carry the engine out to the garage, but I'm suffering again with a tennis elbow, so I thought why aggravate that discomfort ? .. 

- - -

Next.,  closing up of the camshaft's front cover . .


^ this sad little camshaft cover has seen kinder days.  I used wet n' dry to sand it smooth and then polished it up on the mop.  The inside these covers is a machined rebate  ..against which a thrust washer prevent the camshaft from floating about, and that of course (at the rear) keeps the timing chain sprocket in alignment.

There's no mention of adjustment to this alignment in any of the manuals or service sheets, and to be honest I've never checked the chain's sprockets are all in alignment (..perhaps I'll do that on the next engine).  So all I do is to redress its gasket face so it sits flat.  However, if the thrust washer is obviously worn, I take a little more off that gasket face to minimise camshaft end-float ..to between 0.005 - 0.010".

. P1340609s.jpg.859cdf04595c257bc3682efb17718735.jpg

^ With that cover in place (note the tiny 1/4" BSF nuts)  I next fitted the front engine mount. 

The mount consists of a special bracket (which is known as a 'cobra head' due to its shape) bolted to the front of the engine at it cylinder-head joint.  Under the cover is a Metalastic rubber engine mounting block (part # 13/131) ..which is the same type as used with car and marine engines and some machine tools to isolate engine vibration from the chassis frame.   Note ; the cobra head and cover are painted black as standard, and not chrome-plated as on this particular bike.

Above., I'm seen inserting a home-made packing-piece of aluminium between the cobra head engine mount and the front of the engine. This is a tight / clamped in place fit when the mount is tightened as it serves to transfer the torsional moment of force into the cylinder head ..whereby the load on the engine block's mounting boss is no longer a tearing force.  It being only in shear offers far less risk of cracking the cast-aluminium block.




^ Cleverly on these engines, in terms of balance and torque, this engine mount is positioned very high - so the engine effective hangs on it.  There is another engine mount underneath the back of the gearbox, but still - the engine is suspended with its centre-of-gravity below the axis between them. 

The dot at either end of the (red) engine-mount axis line indicate where the rubber engine mounts are on these bikes.  The blue line represents the crankshaft, flywheel and gearbox main-shaft axis, so one can see how the torque reaction of the engine is not in the same plane as its mounts.  Indeed, the engine mounts were positioned to counter much of the torque reaction of an inline engine (..very apparent with BMW motorcycles).  The dot at the end of the yellow lines indicate where there are small rubber side buffers to restrain torsional twist ..which is mostly needed during kick-starting.


^ looking up at the engine - you can see, at the top of the photo, the front engine mount bolted through a boss projecting forward from the engine block.  The black plate under this is of steel which (very importantly) helps transfer the engine's weight load path back to the forward cylinder head stud.  At the sides of the engine (just below the crankshaft) are black plastic blocks which are for the rubber buffers to act against.  (see yellow line & end-dot in the above diagram)


^ Here are the old and new buffer pads. Unfortunately the new ones came a set screw (with 1/4" Whitworth thread) whereas originally there was a 1/4" BSF bolt. 

I re-tapped the new pad to BSF and used the old bolts ..so they at least look standard.  The standard spec bolts were  plain metal finish, but like many details on this particular bike had been chrome plated.

- - -

That's it, it's gone 9.am and so it's time for me to get on with some work.

I have more to report and photos later.

Have a good'n.


Share this post

Link to post
Share on other sites

Just wanted to say, I’ve just read this thread from start to finish. It’s an excellent read.
I’ve been riding bikes as long as I legally could and my dad and grandfather also were keen motorcyclists. I know more about British bikes than someone of my age should but I’ve only ever owned Japanese machinery. Blame my dad and the books and magazines and motorcycles he always had lying about the place.
Anyway, back to my point, great to see the work you are doing BFG. More power to your right elbow, as the saying goes.

Share this post

Link to post
Share on other sites


19 hours ago, Stinkwheel said:

Just wanted to say, I’ve just read this thread from start to finish. It’s an excellent read.
I’ve been riding bikes as long as I legally could and my dad and grandfather also were keen motorcyclists. I know more about British bikes than someone of my age should but I’ve only ever owned Japanese machinery. Blame my dad and the books and magazines and motorcycles he always had lying about the place.
Anyway, back to my point, great to see the work you are doing BFG. More power to your right elbow, as the saying goes.

^ That's very kind of you.   Hopefully these pages will have given you a welcoming insight into the almost touchable heritage of the once great British motorcycle industry,  the innovate design thinking (in context of the 1940's),  and the quality of their products.


Share this post

Link to post
Share on other sites

As things are coming together, in the garage now rather than in my front room, it was time to refit the flywheel, clutch and gearbox before dropping the engine into the frame. The tasks were simple enough and so I didn't expect them to take long ..but again they provided more opportunity to drive me up the wall !! :lol:


^ first job, as always was to clean things up.  I'd had the flywheel lightened by said professional who had stripped the engine and was supposedly rebuilding it. 

The machining work was done but there was no protection from rust.  Still even after a few years in shed storage it was only light surface rust which looked much worse than it was.  Unfortunately he didn't take the opportunity while at the machine shop to also redress the thrust faces on the pressure plates, so they remain more deeply pitted,  but at £140 for the pair of replacements - I hope they are still serviceable. 


^   A handy turntable for spraying (..courtesy of the skip down at the marina) is also surprisingly useful as a riding, sliding, adjustable-height garage seat.  B)  The paint I used was spray zinc, followed by a light coating of silver high temp. 

The standard flywheel is 7/8" ( 22.2mm) thick (front to back) and weighs 9-1/2 lb.  I had previously reduced the thickness down to 18mm thick, which lessen the weight by just 2 lb, but I found it worked well on my S8.   Oddly this one had been taken down to 15mm, which I guess must have been a typo somewhere between myself and said professional,  or he and the machine shop.  That's taking off 4 lb. which of course is a big percentage of the original 9-1/2 lb  ..and more than I would have gone for but as I've now got it - and I'll give it a try.  I'd otherwise have find a replacement flywheel :unsure: ..and to pay again to have that lightened ..to what I wanted.

Note by said professional : " Delivered the flywheel to the engineer (Roe Engineering) in Fleet and briefed them to reduce the thickness of the outer annulus of the flywheel to 17mm. The material is to be removed from the rear (clutch side) face."

Why lighten a Flywheel ?   Well, these low compression engines (6:1, 6.8:1, or 7.2:1 ratio were available) with a 24mm Amal carburettor were, at best, only rated at 26bhp.  The crankshaft is massively heavy and the dynamo armature is then bolted onto the front of that ..so all-in-all there's a whole lot of mass to accelerate, and that absorbs power.  Even just taking a couple of pounds off the flywheel perimeter helps, and in particular makes the engine feel more responsive  ie., it both spins up freer and likewise slows down more quickly - which make gear changes quicker.  These Sunbeams were never designed to be a high performance bike, but a quicker gear-change is definitely appreciated when a laden machine is dragging itself up a long hill and has to quickly downshift to keep pulling.   

The significant  disadvantage  though with a lighter flywheel is not ..as is often suggested - with coarser running at low speeds,  but when starting a motorcycle via kick-start. Then the extra inertia is wanted to carry the engine over its firing stroke a couple of times.  For that the flywheel's greater mass is a boon.  Reducing this one's thickness by 4 lb is I think going to be interesting ..particularly while the engine is tight during its running in period.


^ next up was refitting the clutch mounting studs.  These I cut to length for the skinnier flywheel  (..a mistake I was later to learn !).  Fitted on their star washers + Loctite'd + punched to stop the nuts coming undone ..was surely buttons, belt and braces   :)    Note the masking tape around the boss from when I sprayed it.


^ this is that same boss on the back of the flywheel, showing my work-in-progress polishing up of the surface.  The rear cover of the engine seals on this, and its former aged roughness would prematurely wear that lip seal away.    During final fitting I liberally smear this and the rubber of the seal itself with silicone grease which is excellent high temperature lubrication, and it helps keep rust away.

. P1340677s.jpg.cc8c56ead078cf2170ee995d5b05b8c4.jpg

  ^ The flywheel is now fitted and its 1-1/2" (38mm) central nut tightened with its locking tab folded up.  There is no specification given in the manuals for how tight that nut should be so i took it to 40 ft.lb.   Both ends of the clutch springs were coated with Coppaslip grease as were the sliding spindle of the clutch mounting studs (don't worry these are behind the pressure plate and centrifugal force will keep it from migrating onto the clutch friction pad.   Now laying face down on the floor, so the springs don't fall out - it's ready for the clutch pressure plate. That was likewise zinc painted both sides, except where the clutch friction plate sits.  Unfortunately the clutch pressure face is a little less than ideal, but it's been sanded down and its pitting is not at all deep.  It just looks shyte.     

Note the small square hole in the centre of the pressure plate. This is for the clutch operating push-rod, which comes through the centre of the gearbox main shaft, and is operated by a lever (via a thrust bearing) on the back end of the gearbox.  The push-rod pushes this plate against the springs, which releases the clutch.  It is again a simple design but it works well. 

. P1340679s.jpg.35e4c5d36fa36a93f64d8ad863f9c918.jpg

^ looking clean and ready to go.  I always opt for the Borg & Beck (HB1312) friction plate with its sprung central hub.  The original clutch had a solid hub but I feel the B & B's are a little kinder to the drive-train mechanicals.   I'm led to believe this B & B part was derived from that used in the Bedford HD van  ..with perhaps just 1/4" off its outside diameter and its central splined boss shortened by an 1/8" ?     If I had a lathe, that would most likely be a cheaper source for parts, as this plate cost £66 + P&P from Stewart Engineering,  but as I don't - they are cheaper than some retainers for the correct part.  Btw the solid hub clutch plate for those who want 'originality' is £10 cheaper.  


^ the backing plate is very loosely in place.  No tool was needed to compress the springs, I just push down on one side until I can get a couple of threads on one of the nuts and then work around (diagonally) pushing down and putting on the next nut.  The pressure plate was then tapped into a central position (visual assessment) ..right sophisticated like !.    Then each nut was then pinched down a little until the pressure plate behind could be located on the studs.  Each nut was then wound down (cordless screwdriver speeds things up) until they bottom out and then one-by-one each nut was removed, so the star lock-washer might be fitted and Loctite on the threads. Once all were back in place and the clutch was checked to be central - they were evenly / diagonal sequence torqued to 12 ft.lb.


^ flywheel and clutch done ..complete with a spot of red paint on the flywheel to signify TDC.

..Refitting the gearbox next.


Share this post

Link to post
Share on other sites

OK..  refitting the Gearbox, which according to the notes of said professional was cleaned, opened up and checked to be OK, before closing up again with replacement screws because the originals were a bear to get out.  Apparently the side cover had no gasket, and the gasket face was found to have been damaged. As a consequence there was a lot of gasket goo ..which he'd clean out before fitted a new gasket.


^ Aside from it not having been blasted at the same time as the engine case (which it bolts flat too) - so they would match in texture ..my first impressions are that it looks pretty scruffy for something I had presumed was ready to be refitted. On top, in broad black indelible felt pen were my initials and "No Oil" .. Fair enough but a parcel label or masking tape label would have done.  Perhaps I'm just a grumpy old git.. anyway the writing mostly came off with carb. cleaner.


^ Underneath the side cover was this, which although barely visible was wet with oil  ("no oil" meant inside perhaps ?) :lol:


Inside the bell housing had marks where something had been impacting the inside.  I can't imagine what had been tumbling around loose in there ..but I'd thought it must have made a racket.  That was not at all evident when I bought the bike and test rode it.  There was no mention of painting the inside cover ..but I hope he also replaced the seal. 

NB. the hole seen in the end of the main shaft (spline is for the clutch friction plate) is where the clutch actuating push-rod fits.  It's just a rod with a cap on one end to fit the square hole in the pressure plate and it slides in, nothing more - because at the rear end of the gearbox (see first photo) is where it thrust bearing fits ..and this holds it in position.   


^ yep.. that sure looks to have been professionally recommissioned.!  Old gasket and the gasket faces have not been redressed.  What a sorry state.  Time for me to check what's what with this. 


^ there was oil around each of the screws, but there was at least a clean gasket with sticky goo on it. Sadly there was plenty of the old Red Hermetite evident too.


^ This dirt was just from cleaning the inside of this cover (it was clean parts cleaner).  Anyway the kick start shaft return spring and its bronze quadrant (to the left) look in good shape, as does the gear selection quadrant. The spline on the end of the gear-change shaft is worn  ..and if I'd had another one I would have swapped it out.  This side panel may be removed with the engine and gearbox in frame, so for the time being I'll put it together and use it. I can always change it out another time.  The kick-start shaft has an amazing good spline on it. That's rare.   


^ there was Red Hermetite in a lot of the corners and gasket faces hadn't been redressed at all.  Here I've run over this one with emery paper on a (carbon fibre - very flat) block to remove the shallow scratches and to examine the extent of damage.. What on earth causes this ? 

Anyway, there's not a lot I can do about it - as I'm not sure the gearbox would go back together again if I were to take 0.030" off this face ..to cut back through most of the damage.  Instead I cleaned out the deeper chunks and filled them with Araldite with ground aluminum.  There is actually a unbroken, albeit convoluted, line between the inside and the outside of this case, so in theory it should seal.  I'll double up on the gaskets to give it a little more compressible 'give' when I refit it.

.    P1340659s.thumb.jpg.5fecfb8c263fb17e59b4e13045402bb0.jpg

^ As standard the gearbox doesn't have a breather vent and so as it get hot, oil tends to be pushed out passed the seals (or gasket), so I do this little mod to my bikes.


You can just about see the little red pipe I've glued in through the top, and chopped off to length. Its end sits less than 1/4" above the case, bu that's enough to stop water running inside.  The drilling goes into the gearbox's rear chamber, above where the kick-start quadrant fits, so it's sheltered from the oil being flung around the gear train. In short ; it doesn't spurt oil - but it does vent.

You might also note I got rid of every last remnant of the old gasket goo ..and I've started cleaning up the cases. The two access covers ..one in the bell housing for viewing the flywheel marks to set the ignition timing and the other being the oil filler orifice, have had their gasket faces redressed and the covers themselves smoothed of scars and polished up again. And even the bolt heads now match. Things are beginning to look 'restored'.


^ Because of the damage,  I've used two gaskets. one gooed to each spotlessly clean aluminium face. but with no gasket goo inbetween them, so it will come apart when called to do so.  The set screws are countersunk and the threaded holes into the case were yuk (chose any appropriate word to your liking, cause it took me quite a while to properly clean them out).  Because the screw holes are not blind, oil tends to seep passed them, and then the only seal is the countersunk head of the eight screws.  I'm using Wellseal on the threads and then again at the top by the countersunk head. I rely that working better than nothing.!


^ next up was the said professionals attempt at sealing the oil level plug.  The bolt is not the correct one, there's a split lock washer over a fibre washer (I'd never seen that one before !) and then some sticky grey stuff on the thread.  More yuk of a different flavour !


Ok so it doesn't look original (It ought to be cast finish) but it does now look respectable.   The red breather pipe I've touched in with a dab of silver paint and where I place it is nearby where the clutch cable runs, so really it's barely noticeable when the gearbox is back in the frame and the battery box is over it. 


^ Engine and gearbox ready to mate.  (. . you guys have got a one track mind !) 

With the engine face down like that is the easiest way to drop the gearbox on.  The clutch push-rod is loosely slipped into the gearbox main-shaft and as the gearbox casing is lowered onto the engine's studs its square-peg-end is manually located into the clutch pressure plate.  The weight of the gearbox pretty much does the rest (note the Coppaslip on the engine's studs). 

Aside from the diversionary work on the gearbox itself,  all went well.  but as I say ..

4 hours ago, Bfg said:

..it was time to refit the flywheel, clutch and gearbox before dropping the engine into the frame. The tasks were simple enough and so I didn't expect them to take long ..but again they provided more opportunity to drive me up the wall !! :lol:

so lets start with this ..


^  Gearbox off again ..because the stud pulled out of the engine..  Did I mention before ..not to remove them unless absolutely necessary.. 

I then fitted a helicoil type thread-insert with lots of Loctite., and then immediately refitted the stud with even more Locktite.  Thankfully because I used to be in business I had a thread-insert set with 3/8" Whitworth ..in stock.  Still, it was a pain to do in situ and without taking the clutch flywheel and rear engine cover off to get to a flat reference face ..for squareness in drilling.  However, looking on the bright side, this was a through hole ..so the bits of swarf were easily cleaned out.

It went OK., but the bell-housing's hole did require a little 'easing'  ..because with a protruding 3" stud length, it only takes a degree or two off-square to start binding up.

Job done !

Gearbox back on again.

. . .

. .


Gearbox off again !

Because then the top stud pulled out of the engine block.



That's enough for today..


Share this post

Link to post
Share on other sites


..  Following on. .  the top gearbox stud having stripped out of the engine block.


For a while I considered just ignoring it.  After all the early S7 model had just four bellhousing studs and didn't have this top one at all.  The engine is supported from the front and the gearbox at the very back ..so in practice because this engine / gearbox is hanging ..this top stud doesn't do much at all.   However., I'm me and while I had the engine on the floor rather than in the frame I thought it best to deal with it as well as I might.   Firstly that meant stopping bits of aluminium falling inside the engine.   Yes unlike the previous stud to pull out, this one's tapped hole is through drilled to the cam-chain chimney. 


^ I neither wanted to dismantle what I'd already put together, nor did I want bits of aluminium inside the engine or the clutch.  So even before I pulled the stud out - I had masking taped through the inspection orifice and down to the back side of this hole.  That was much easier done now than later - because there is still no engine oil in that space. Over the top of that tape, and extending down even lower I used duct tape which I further hoped any bits will stick to.  The clutch and down behind the flywheel, where the engine's rear oil seal is, were covered with a newspaper and then over that with an old rag. 


A trick I'd learn from experience with these engines was ;  rather than drilling the hole for the larger tap (necessary for the thread insert) - you wind the stud IN  ..to completely strip the old thread out.  This way, because you're not drilling (at all) - it can't be out of true !   I don't know if this works with other sizes or threads like BSF or metric, but it certainly does with 3/8" Whitworth into aluminium - the stripped-out hole is fine for the enlarged tap used for the thread-insert. 


.P1340701s.thumb.jpg.4d2b94b4e49b6a7b9c1150f20c24c6b0.jpg   P1340703s.thumb.jpg.1875a5fdb521f4dd3afcaefcc2079f90.jpg

^ Tap Tap                                                                                                                        ^ Thread insert here  ..lots of Loctite too

I replaced the stud immediately, again using copious amounts of Loctite so it would all glue together ..hopefully firmly.  Perhaps this is a situation when rather than medium-strength Loctite, I ought to have high strength. ?


^ The one issue I did have was with the tab on the thread insert, which is supposed to be broken off.  But I didn't want that piece of wire dropping down inside the timing chest and it is of stainless steel ..so I couldn't grab even with a strong magnet.

It's tucked in to the side of the chimney so it'll not get caught (unless the cam-chain breaks !) so I've left it in there.  The thread inserts went in smoothly without binding and so unless the stud is pushing against it.,  it ought to be unstressed and not break off.  If it does and I'm unlucky then it may drop into the chain and lower sprocket. The direction of chain's rotation passed it is downwards so it might just be deflected straight down into the sump.  Unfortunately without taking the cylinder head off again I'm taking a risk.  If it had been a customer's bike I would have to strip it down, but as it's my own and I'll accept the risk and potential consequences.   Hey ho.,  whoever said I was a perfectionist ! ?


^ stud in and bits out..  Time to refit the gearbox again. 


^ almost ready to rock n' roll in the frame.. Just need to fit the clutch push-rod's thrust bearing and actuating lever. 

OK., where's the thrust bearing ?  ..and where's the special stud / axle for the lever ?

I find it a just little* frustrating when parts are not in with the rest of the bits for that engine.  It's something that I generally have under control ..since I acquired 40 or so robust plastic box-trays,  previously used on a conveyor belt.  They help me keep all the bits of loose assembly all together.  Of course that goes to pot when things go out of the door, such as to the said professional who was commissioned to build this engine & gearbox, and likewise when parts go off to a machine shop.. ( Note to self : chase up TR4 pistons and con-rods that never came back from the machine shop in Colchester before the lock-down ).!  

Fortunately I had a couple of spare thrust bearings, and I have a spare un-restored engine with gearbox that I could steal the lever's special stud from.  I didn't want to disturb that .. but perhaps its better to do than to repeatedly bang my head against a brick wall because I no longer have the part from this engine. 

So.., moving on..


. P1340709s.jpg.904f249fbf603ded31412547b37ef4eb.jpg           P1340710s.jpg.8d4a3eb54bf551da039cc0b3cf8c9fac.jpg

 ^ a spare thrust bearing (right) which fits inside a sleeve (left, shown assembled).  The drilling in the centre of the hub takes the end of the clutch push-rod which spins with the clutch.  The bearing is secured in the sleeve with an internal circlip, and the whole assembly when greased slips into a bronze bush pressed into the back of the  gearbox.  With the tiny ball-race spinning all the time you'd think it would soon wear out, but because there is only ever any load on it when the clutch is activated - they do last exceeding well.  


^ the aforementioned special stud, which is the axis for the actuating lever, the bottom of which acts against the thrust bearing and therein the push-rod.

Problem is that when I put it together it didn't work. !

I thought I'd assembled it correctly and that was 'foolproof ' ..but the angle of the lever was sloping too far forward.  It is pulled by cable from the handlebar lever, and so it should start off leaning backwards and pull forward towards 90 degrees ( to the cable) when activated.    What then was wrong ?  Were the parts of such different lengths that they had to be a matched set ?  I'd not had this issue before.  


^ I did discover, by going through data and service sheets and all my manuals, that the lever was reversible .. up until 1952.  A later lever is shown (left) and you can see around the bottom pivot is a squarer shape.  (NB. The plain steel or black painted finish was standard).  The one off this engine (chromed) has a rounded pivot and that's reversible.  So I turned it around.. 

It seemed to be about the angle now,  but I was still unsure.  So I called for help .. " Nudge ". . .


^ she was asleep in the house but willing came to my assistance. . .

. P1340717s.thumb.jpg.6e8f0202030c7293eac7dcb96b972e21.jpg

^ Clutch cable connected to the activating lever .. and you know what - I was right  .. It didn't work.

So, the gearbox had to come off yet again. 

             ..... I was flummoxed but then also happy - because I'd found this before I'd put the engine in the frame, reassembled all the ancillaries and connected everything up. :lol:   Q. Does that smiley look happy or hysterical to you ?  

Pulling it apart would wait for the next day..  I needed to think before I acted.   

            Not that it did any good because it was only when I removed the gearbox did I find this . .


^ coil bound clutch springs.  They would move a little but not enough to release the clutch.. 

But why ?    Checking measurements wasn't giving me the answer.  And yet it was there right in front of my nose, even after I took the clutch apart again.  I could work out what was the problem ...and I could even rectify it,  but I could not see why


So I pulled my spare (and previously undisturbed) engine and gearbox apart,  removed the clutch and fought to get the flywheel off (..it's probably been on there since 1954, as the nuts and tab washer reveal absolutely no sign of it having previously been disturbed).

But now I had a standard flywheel to compare.  Finally the penny dropped and I realised what had happened 

. . .

. . 

. P1340780as.jpg.aaea1296e9d91927940278cd9e5e913b.jpg

^ the key to the mystery unfolding was in comparing the standard flywheel (left) with the one I myself had had lightened.  In rounded figures, the standard flywheel is 7/8" (22mm) thick and mine had been reduced to 18mm.  This was done by removing the studs and taking the metal off the back face / gearbox side.  However you can see the studs on the standard flywheel are recessed whereas on mine they sit flat to the surface.  The clutch pressure plate (represented by the dark blue line)sit on the ledge of those studs which are the same height on both.  And the clutch springs sit in the 1" holes (buckets represented by the grey dashed lines) spaced inbetween the six studs.  The bottom of those holes are untouched and therefore the height (red arrow distance) between that bottom and the pressure plate ledge is the same on both these flywheels. 

On the flywheel 'said professional' had machined was reduced in thickness by a further 3.25mm.  And its studs sit on that lower face ..which in turn means that the clutch pressure plate is closer to the bottom of the spring holes - and so the (red arrow) height is likewise that amount less.  This plus the new clutch plate being another .75mm thicker meant that the distance was overall 4mm too tight.  

And, in the orientation of the gearbox on the engine - this takes the clutch pressure plates forward by that amount ..which is why the actuating lever lent all the way forwards.  It was as if the push-rod was 4mm too short. 

I had already understood what the problem was, and even had (sort of) rectified the issue (below) ..but I hadn't worked out how it had happened. 

Now I know to advise anyone not to machine this face any lower than the level of the recess those studs originally fitted onto.  Taking 3 - 4mm off works but taking 7 or 8 mm off the thickness of the standard flywheel ends up with this sort of problem. 

- - -

Lightening the flywheel :

The reasons for why I like to light my Sunbeam's flywheels and also the disadvantage have already been discussed, so I'll not go through them again - but here are a few observations.

  • The studs will have to be removed and the boss on the engine side needs to be undamaged - otherwise the crankshaft seal will get chewed up or prematurely wear out.  I polish this face up so it shines like chrome and then apply silicone grease to it and the seal during reassembly. 
  • The standard flywheel is 7/8" thick and 8-3/4" diameter (22mm Thk and 222mm dia.).  The clutch (friction plate) diameter is 6-3/4".
  • The standard flywheel weighs about  9-1/2 lb. That may not seem very heavy but in combination with a heavy crankshaft and the dynamo armature there's a lot of mass to rotational accelerate & decelerate when trying to quickly change gear.
  1. Reducing the thickness of the flywheel to 18mm (4mm skimmed off) lessens the flywheel weight by 2 lb.  That doesn't sound much but it is 21%  ..and being away from the crankshaft axis makes a noticeable difference in interia.  There may be production differences but skimming (turning) 4mm off the rear (gearbox / clutch side) face should take it to the same level as the bottom of the holes the clutch studs were sitting in.  Do NOT  take more depth off than this, otherwise there are issues with the clutch operation and its springs binding up.  
  2. If more weight-saving is sought, then 10mm can be taken off  the flywheel's outside diameter.  5mm off the radius clears the studs and spring positions. This will save 1.3 lb if the flywheel's thickness has not been reduced from standard (22mm),  and 1 lb if  the flywheel is also reduced to 18mm thickness. However, taking mass from the outside perimeter will have maximum effect on freeing up inertia. 
  3. If even more weight saving is required, then another 2mm (maximum) might be turned off the engine side of  the flywheel. That will take of another 1 lb. of weight out of the flywheel and ought to still leave a safe 3mm thickness at the bottom of the clutch spring holes.
  • If each of the above three reductions are done then 4 lb has been removed which is a massive 42%.  This is the weight of the flywheel I'm just about to try, but I suspect it will make starting the engine very much more difficult, particularly while the engine is tight from having been rebuilt.    

- - -


And so how did I try to 'fix' the issue of this incorrectly machined / particular skinny flywheel (just 15mm thick).

Well.., I simply packed a couple of washers under the studs.. 

.P1340739s.thumb.jpg.299ed4fab933442aa8d0d684e47b218f.jpg    P1340794s.thumb.jpg.301bf90b0a5ea13ffefc153b3d49abf5.jpg

^ packing the studs up higher by 3mm on two washers and another 1mm washer at the top, under the pressure plate itself, will correct most of the error made in over-machining this flywheel.  

The solution ( fix ) is not wholly satisfactory but I'll try it.   I'm planning to run-in this engine/ gearbox in Nudge for the first couple of  hundred miles, and then to pull it out again, so I'll check this clutch then to ensure nothing is twisting or loosening.  Of course during running-in,  I'll be tuned-in to listening to the engine, clutch, gearbox for any fault.   Still I think it pretty likely that I'll have to scrap this flywheel and find another. 


Share this post

Link to post
Share on other sites


Just a quick report this afternoon . .

The clutch now works ..with 4mm of washers in place, under the studs, to restore the working length in which the clutch-springs sit.


^ trialing it with the studs sitting on two washers, which together are 3mm in thickness, and another 1mm thick washer tucked in under the pressure plate, we can now see a visible gap between the spring's wires / for the coil to compress into.

.   P1340796s.thumb.jpg.2ef29085d1ca473942ac1bb151d1eca5.jpg 

^ temporarily reassembled with the gearbox back on and the clutch cable attached - it worked.  

. P1340799s.thumb.jpg.a7ac5a7b5b8d4682d770b5d998d9dd4f.jpg

^   the cable is correctly adjusted in this static condition / without it being applied, but as you can see the screw adjuster is right the way out.  Ideally the adjuster's thread should be 3/4" further in.   This happens to be a well used cable ..so it probably wont stretch any more.  For better leverage - the actuating lever ought to be sloping back by 5 degrees so, when applied, it is pulled to this angle ( 90 degree to the cable). 

When the clutch is fully applied (lever on the handlebars) - the top of the actuating lever is pulled forward by 3/4" (19mm), which in turn moves the thrust bearing by just over 1/16" ( 2mm).   And that's plenty to release the clutch.  Conclusion then is that it will work, but I may need to shorten the cable. It appears that the clutch pressure plate is still about 2mm too far forward.  Fortunately with this design - it will move backwards as the friction-plate wears ..and the cable will get a little tighter rather than looser. 

I've lighter clutch springs on order, which I've used before and which work well with the Borg & Beck clutch.   That won't change the geometry but hopefully it means that I'll just have to remove the gearbox and clutch one last time.

Have a good weekend



Share this post

Link to post
Share on other sites

Good morning all,  nice warm weather eh B)  This past weekend I've been playing around a bit in the garden ..insomuch as the 'wildlife' pond was dry of water ..as the hose feed to it, from the garage roof's water butt, had come apart.  Aside from that - I made only a little,  but now quite visual, progress with the bike engine.  Self motivation is really lacking - but I try to take things another step forward each day,  however little  ..it will then eventually get done. 

First up.,  I tried to break off the tab wire on the back end of the gearbox mounting stud's thread-insert.  I reasoned that if I broke it off now, while the engine was dry of oil, then that piece of wire ought to fall out if I inverted the engine.  Worse-case-scenario would be that I'd have to take the sump and baffle plate off again to find it.  But hey ho - the bloody tab wouldn't break off. :angry: ..so I've left it there. 

The new lighter clutch springs arrived so I've now fitted those.  Stewart Engineering say they are 20% lighter (force needed to compress them) ..and true enough comparitively squeezing down on them, on the bench, you can feel it is indeed lighter than the original.  Interestingly ; their spring's wire diameter and number of turns are exactly the same ..so the old and the new look exactly the same even when compressed in a vice.  I had expected its wire to be of smaller gauge .

And I also reversed the clutch actuating lever so that it leans backwards, which ought to result in a decent amount of screw adjustment on the clutch cable. The lever was wired right the way forward (clutch activated) in readiness for lowering the engine into the frame.

Finally then.., it was time to drop the engine/gearbox into the motorcycle frame.  This is Pudge's engine and gearbox but, because her own cycle parts are still dismantled (subsequent to being restored / refinished) - I'll use Nudge's frame / cycle parts for the first 200 miles of running in.  I'll then to swap the engines and run-in Nudge's rebuilt engine.  In this way I can be focused on just the running-in of the engine - without also having to make adjustment or have to keep an eye out for steering, suspension, brakes, battery charging & electrics, fuel or whatever  ..which sorta makes good sense to me. :blink:



^ Unusual and very advanced for the 1940's - the Sunbeam's frame is duplex ..which essentially means it has two down-tubes (from the steering head) and lower frame members - and the engine sits inbetween them.  These frames are structurally stiffer than those with a single down-tube and the engine's c. of g.  is lower.   So, with the engine lowered via block n' tackle, from a garage roof-beam, and the bike itself on its side-stand to lean it to one side - the engine comes in from the right hand side. The extended sump does need to be lifted over the frame tube (itself protected from scratching with the leg cloth of a pair of jeans).  

I have lifted the engine /gearbox in by hand before now but the block n' tackle (or in my case winch) makes life easier.  So the task is not difficult ..if you happen to have three pairs of eyes to ensure the frame doesn't get knocked and scratched.  But as I only have one pair - I take things very slowly ..inching the engine and gearbox in, and use rags to avoid damage.   

A little lateral thinking..  with the bike on the side-stand it's very easy to roll it forward or back an inch or two as required,  &/or to grab the bike and slide the back-end sideways to position the frame under the pulley block. 


^ still on the side-stand and with the back-end of the bike slid around - the gearbox tucked itself in. The engine was then lowered to be inbetween the down-tubes.  Note the clutch-actuating-lever wired forward so as to not scratch the rear mudguard.  The cord carrying the weight of the engine and gearbox is a little lighter than the chain more commonly seen when putting a car engine into its chassis.!   I've found the cord slung around the Sunbeam's rear exhaust and dynamo studs (as shown) work well in regard to the engine/gearbox's c. of g. and the cord being to one side of the top frame tube.   

Anyone who knows these Sunbeams may also have noticed that the electrical box (resting on the saddle) is not with / bolted to the battery box.  Usually they are but because I know I'll need access to adjusting the clutch cable and to tighten-up the rear cylinder-head nut several times during running in, and then that this engine will be swapped out again sometime soon - then it makes sense to get rid of that (the battery box) obstacle. 

As an aside ; modern 6-volt gel batteries are tiny in comparison to the originals, and I had planned for some time to fit a pair of those down in the bike's tool box (seen next to the left hand footrest in the first photo).  That would lower their c. of g. and free up the sizeable and more accessible battery box to be used for tools and over-suit. This seems a good opportunity to make that change.


^ sling removed and the bike is now sitting upright on its centre stand.  As you can see these engines sits nice n'  low inbetween the frame's down-tubes.  The engine's top-front mount and the gearbox lower-rear underside rubber mounts are suspending the weight, which together with the engine's front-bottom 'snubbers' (side-ways control rubber blocks) are adjusted to set the engine & gearbox centrally and square to the frame.   We are finally getting there.!

Today I hope to get some of the ancillaries back on.

Have a good'n.  B)


Share this post

Link to post
Share on other sites

What a cracking thread to read. Reminded me of mine in the mid 70s (photo), the nephews now mid 40s 😀 Mine was a bit naughty and snapped its crankshaft at the crank journal, it kept running although a bit rough 🤪. I was alerted by the charging light coming on as it destroyed the dynamo. Found a block complete with dynamo minus head at a local scrap yard.

Probably one of the comfiest bikes I've owned. I hope you enjoy many happy miles on yours. 👍 


Share this post

Link to post
Share on other sites

^ Excellent - Thanks Stu.  I see your Sunbeam was taxed to Sept 1985  ..I wonder what happened thereafter. 

I've heard of crank's breaking but have never come across one or know of anyone it actually happened to - I thought it must be just another fable.  I do wonder why any crankshaft breaks though ..they are substantial chunk of iron.  The original front bearing was a ball race and this was changed to a roller around about the date of your bike (1951) so I guess there must be something in how the crank' flexes.   


Share this post

Link to post
Share on other sites


Yesterday saw me wasting an afternoon doing a two-step shuffle around the engine mounts and clutch,  insomuch as I'd taken a step forward and then needed to take two steps back. . .

My thoughts regarding car and boat engine rubber mounts is rather basic in-so-much as I plonk the lump in, adjust their height and do up the nuts. Of course many motorcycle mechanics have very little experience of them. There's just two on these Sunbeam motorcycles, and those are both adjustable and interlinked.


 ^ under the gearbox - the top plate of rear engine mount has a sideways slotted hole, for lateral positioning of the gearbox in the frame, and a fore n' aft slotted hole in bottom plate to allow for adjustment in that diagonal direction.  A thicker rubber moves the whole engine/gearbox assembly forward & upwards  ..and the way I just happened to put this engine in (not knowing which were the original mounting rubbers).. the front engine mount rubber was being pushed upwards relative to its attachment point on the frame (ie., in shear).  With it only being 1/8" out of alignment - it would probably be fine.  But it wasn't right and so the rear mount had to come out. . 

. P1340822s.jpg.a9c2c2ebdcca6927e2f9e5d7d23926cf.jpg

^ the rubber (right)  in the rear mounting is just a little thicker than another I had on shelf (left).  The difference is less than 1/8" (3mm) but when the lesser (15/16" deep) one was fitted - it correctly allowed the engine/gearbox to come down and rearward by that amount which then positioned the front mounting rubber to sit nicely unstressed (no shear) .

However., at the front mount I had a different issue..


^ 1. The front-engine-mount plate is bolted to the frame and has a slotted (sideways) hole for positioning the engine laterally in the frame.  However, the metal cap over the rubber-mount prevented much adjustment ..because it fouled the plate's mounting bolts (1st piccie, red arrow).  I removed those bolts and shaved some thickness off the heads but that wasn't enough. 

2.  I'd fitted a non-metallic penny washer on top of the cap, between it and the engine's 'cobra head' bracket.  This added clearance and helps avoid the cap vibrating / ringing like a bell.   This  'insulating washer' (part # P4/032) was specified on early engines but deleted on later ones. In the parts diagram it's shown under the rubber mount, so between it and the frame's bracket. But it doesn't make sense to 'insulate' a rubber mount from the frame.   As there are a few errors in those parts book illustrations, I made a logical assumption ..and got it wrong. 

So that insulating-washer should go under the cap - to raise the cap's height above the plate mounting bolts.  On later engines it could be deleted simply by making the cap's skirt shorter, or else by using a slightly thicker engine mount rubber ..very much like the one I had put under the back of the gearbox ! :unsure:

3.  I've resolved the issue by fitting the black insulating-washer under the cap, where I now think it ought to have been, and I'm using a white nylon washer on top of it to give me the clearance between the cap and the engine's cobra-head bracket.

4. Now it's all reassembled and the clearance between the cap and the bolts are good for sideways adjustment.  And the rubber mount is sitting nicely unstressed - job done. 


Next was to position the engine and gearbox in the frame . . .


^ the Sunbeam the engine is positioned slightly offset to the right hand side of the frame so that the driveshaft (left photo) clears the rear mudguard and the tool box (right photograph)  is away from the gearbox side case.  This may seem blatantly obvious., but almost every gearbox I have seen has a groove from where it's been rubbing against the toolbox.  Owners and mechanics, instinctively it seems, want to position the engine centrally, but that doesn't take into account the lateral movement offered by rubber mountings.


At the front of the engine  (below)  it is subtly done. . .  


^ With the bike on its centre-stand (sitting upright) and the engine suspended from the top  engine mount.,  its lateral adjustment is to used to position the  lower  crankcase evenly between the frame's down-tubes (left photo, red arrows).  The conical rubber 'snubbers', seen either side of the crankcase, are only there to stop the engine from swinging like a pendulum, and not to adjust the engine's position. Note how the engine is positioned evenly between the frame ..but the exposed screw-thread of the bike's left-hand snubber is more clearly seen.   Once the engine is located (by the mount) I wind the snubbers in until they lightly touch. There's no compressing those rubbers and no gap. The outer lock nuts are simply pinched-up to hold that adjustment. 

The subtly of design is that the engine lower cooling fins / stiffening ribs have been cut away (only) on the right-hand-side of the engine block.  So even spacing (first photo above) the engine is on the one side between the ribs and the frame, whereas on the other - it is between the smooth crankcase and the frame. The detail is largely unnoticed ..particularly when the carburettor and its teardrop-shaped air filter,  and the exhaust-down-pipes are fitted onto the right-hand-side of the engine, where the ribs are missing. But the result is that the engine and gearbox sit to the right hand side of the bike's frame.   As an aside On the early S7 engines those ribs were not stopped short in the casting, as seen above, but were locally cut away by hand. 

I have the top-Rear snubbers to fit yet, but the engine is now positioned... gearbox end first, then the front engine top mount, followed by closing up the snubbers. 

- - -

Before I moved onto fitting the rear snubbers,  I first wanted to connect the clutch cable and to adjust that.


^ I had reversed the actuating lever - because I was out of adjustment at the cable adjuster  ..but now when connected  there wasn't enough free play in the cable to release the clutch.  So, the blinking thing had to come off again.! 


^ however..  reversing that lever was hampered by getting in to undo that lock nut.  It's so close to the gearbox case that you cannot get a ring, a box spanner, or a socket onto it.  Together with the gearbox, the rear mudguard, and the frame in the way - access is very limited.  

I'd had this problem once before but abused a screwdriver (as a drift) to undo the nut.  A similar issue is with the clutch cable adjuster, which again is very awkward to get to when the battery-box is in situ immediately above it.  They both take a 1/4" Whitworth spanner, so this time I thought I'd modify one to better fit . . 


^ this is a 13mm spanner which fits the cable adjuster fine and with a little filing of the lock-nut in question likewise works.

. P1340848s.thumb.jpg.0cf9ce9612cfc0845dc3c5111a4fda40.jpg

^ lever is now reversed ..and the modified spanner works great to re-tighten the lock nut. :cool:

Job almost done.


^ I've used a stepped spacer between the cable's outer and the adjuster screw.  This I think came from a throttle cable where it goes into a twist grip.  I had to file it for a wider slot ..to take the thicker gauge of clutch cable,  but with the clutch cable correctly adjusted (with a just-perceptible amount of play at the handlebar lever) - the clutch action is now really good and not too heavy.   It's not a brilliant solution though - as the cable forward of the adjuster has to contort more than I would like, but it works.  I'll use it like this until this engine is swapped out after its initial running-in period.  And we'll then see what's needed with this bike's original engine and gearbox. 


So progress was made, although I had expected to have done it in half-an-hour ..rather than having to dismantle engine mounts and clutch levers again.  Hey ho., that's how it goes some days  ..and I'm pleased with the modified spanner and that I managed to keep my temper all afternoon  ! 

That's it for today.  Now I must go and do some more .

Best regards, Pete.    

Share this post

Link to post
Share on other sites

Big catch-up on this thread - excellent work going on here. This is going to be the best Sunbeam in the world by the time you are done.

Couple of thoughts - solid copper head gaskets are quite easy to  anneal with a modest butane blow-torch. Copper has a really low heat capacity and gets red-hot very easily. It doesn't seem to matter if you don't get all of the gasket red hot at once.

Piston ring compressors - ? Cable ties work well for this if you only do it occasionally.

Share this post

Link to post
Share on other sites
23 hours ago, plasticvandan said:

I have two 4.5a alarm batteries on my Ariel,that give the 9ah

Likewise I use two 6v - 4.5ah gel batteries wired in parallel.  I'm sure they were being sold for use on a moped but might equally be suitable in an alarm or night-light security box.  They were pretty cheap off e-bay and yet they hold their charge better than lead-acid batteries when a bike is laid up without use for a few months.


^ two 6v - 4.5ah batteries wired in parallel, as fitted into one of my customer's bikes, were wrapped n' packed to stop them rattling around in the large battery box.  On subsequent bikes I gaffer-taped them together which was a bit neater.  The only issue I have with them is that their spade terminals are so darn small.


20 hours ago, Asimo said:

excellent work going on here. This is going to be the best Sunbeam in the world by the time you are done.

Couple of thoughts - solid copper head gaskets are quite easy to  anneal with a modest butane blow-torch. Copper has a really low heat capacity and gets red-hot very easily. It doesn't seem to matter if you don't get all of the gasket red hot at once.

Piston ring compressors - ? Cable ties work well for this if you only do it occasionally.

^ Thanks, that's very kind of you.  My bikes are always done to a tight budget - so I'd guess there will be nicer bikes out there  ..but after six months on the road mine I hope they'll simply be a good ride ..rather than a trailer queen or an ornament mounted on a plinth in the study.

I have tried on several occasions to anneal the copper head gaskets with butane and with plus-gas but I couldn't get the temperature hot enough. It partly anneals but insufficient for a cylinder head gasket.  I do use the blow torch for copper washers though without problem.

Perhaps you can show me how you use cable ties for a ring compressor, is this in conjunction with strips of steel placed upright ?

Thanks,  Pete.   


Share this post

Link to post
Share on other sites

I just use one tie per ring. Takes little pull on the tie to close up the gap. Each tie is cut off in turn as it's ring enters the bore.




As for the gaskets, I suppose the only ones I have anealed with a small butane torch have been for sidevalve and cast-iron lawnmowers. 

Not exactly a demanding application!

Share this post

Link to post
Share on other sites
On 5/21/2020 at 12:03 PM, plasticvandan said:

Regarding batteries, I have two 4.5a alarm batteries on my Ariel,that give the 9ah it should have but still fit inside the dummy battery box.

I've just ordered a couple of these 6v - 14ah batteries, for the two bikes I'm working on.  I was about to order 6v - 4.5ah batteries as I've used before, but these work out cheaper (£16.90 each as opposed to two x 4.5ah at £9 each) so I've saved a couple of quid,  and instead of each bike having 9ah they'll now have 14ah,  and  I'll not have to make up the wires to link two batteries in parallel.  That works for me. B)

. 496256498_6v14ahgelbattery.jpg.5cdc92ab48cf12cda8291b734f5332bd.jpg

ebay link < here >

Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Create New...