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Garage Diary : Sunbeam Motorcycle resto's..


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On ‎3‎/‎2‎/‎2020 at 11:12 AM, Bfg said:

Only in the latter half of the 1960's did Japanese motorcycles really make an impact. They too started off with commuter bikes, but also developed inexpensive but quick 2-strokes. Their post-war investment in press machine tools and die-cast aluminium parts meant their production tolerances were relatively excellent, as was oil tightness and reliability.  But from a marketing point of view they were pretty low profile in Europe until their turning point - the four-cylinder motorcycle.  Only from the early 1970's (some 25 years after the war-time market prediction & decisions) did the British motorcycle industry fail to keep up. 

One problem which should have been foreseen was the abandonment of the moped/light motorcycle market to the Japanese. There was no serious attempt to compete with the Japanese; all they could offer was Bantams and various Villiers engine bikes. The Raleigh Runabout vs the Honda Cub; which would you have?

The British bike industry relied on brand loyalty, but if you don't have a serious entry level bike how do you build this loyalty? The youth buying his Japanese moped which was clean and reliable would not consider moving onto a  British bike when he had seen what could be done. The Japanese built up their own brand loyalty and the CB750 was launched at exactly the right time to cash into this loyalty. Back in '69 would you really buy the Rocket 3 when you could get a CB750? Particularly when your CD175 was still ticking along nicely (unlike your mates Bantam).

And the Japanese, in particular Honda, looked far beyond the biking fraternity for sales. 'You meet the nicest people on a Honda'.

On ‎3‎/‎2‎/‎2020 at 12:14 PM, somewhatfoolish said:

Industry did most of it to itself; Bert Hopwood was there and wrote the book. Complacency, lazy management, intransigence of unions laid the groundwork and the short-termism encouraged by various governments discouraged investment and finished the job.

Good book - I've read it several times although he is a  little bitter in places. The top heavy McKinsey inspired management structure in the 60's seemed to be a major part of the problem.

Image result for bert hopwood book

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10 hours ago, martc said:

One problem which should have been foreseen was the abandonment of the moped/light motorcycle market to the Japanese. There was no serious attempt to compete with the Japanese; all they could offer was Bantams and various Villiers engine bikes. The Raleigh Runabout vs the Honda Cub; which would you have?

The British bike industry relied on brand loyalty, but if you don't have a serious entry level bike how do you build this loyalty? The youth buying his Japanese moped which was clean and reliable would not consider moving onto a  British bike when he had seen what could be done. The Japanese built up their own brand loyalty and the CB750 was launched at exactly the right time to cash into this loyalty. Back in '69 would you really buy the Rocket 3 when you could get a CB750? Particularly when your CD175 was still ticking along nicely (unlike your mates Bantam).

And the Japanese, in particular Honda, looked far beyond the biking fraternity for sales. 'You meet the nicest people on a Honda'.

Good book - I've read it several times although he is a  little bitter in places. The top heavy McKinsey inspired management structure in the 60's seemed to be a major part of the problem.

Image result for bert hopwood book

I cannot disagree with this in principle,  but I feel it's missing an important element ..insomuch as in the mid 1960's there was war between Mod's and Rockers. That (shameful behaviour in Great Britain ! ) has largely been brushed under the carpet to be forgotten - but it was a really big thing at the time with some very violent clashes, and the police often caught inbetween the two fractions.   And the Mods of course were mainly riding Italian made scooters. The point being that the lower end of the market had already been lost to European imports before the Japanese products arrived in force.  

A further and very significant impact of these conflicts was that many of us wanted nothing to do with it.  And all bikers were ostracised by the general public,  by car and lorry drivers, to the point where 'accidents' occurred ..involving bikers being knocked off.  In the meantime of course - the Police watched every biker with great suspicion and for the slightest traffic violation. 

Myself and many others sought to distance ourselves from those cultural stereotypes ..and in the first instance - this was done both by wearing nylon biking jackets (very often blue) ..as opposed to khaki parkas (worn by Mods) or the black leather jackets (worn by Rockers).  And we chose an alternative style of bike (not a scooter, nor British iron).  I started off on a Honda 175 (Cd and then a CB).   Clean and quiet - we were clearly not troublemakers - we were simply the new generation of commuter motorcyclist.

Bottom line, the Japanese product didn't entice many of us, but the bad name ' bikers' got, due to the riots - drove a wedge between us and traditional British Iron.

As it happens I liked small Hondas but perhaps because I was very tall but skinny, I never got on with their bigger bikes.  I didn't like their weight, nor the high frequency vibration, or the sound, nor their pressed metal frames, the amount of crappy chrome, nor the lacquered engine cases, nor their handling, and especially I did not like the tyres they were supplied with.   So I went from the Honda CB173 to a Norton Commando 750 Combat (albeit still wearing the blue nylon jacket) and soon thereafter to the 850 Norton Interstate.  I did have a Triumph 750cc T140V Tiger (which blew cylinder head gaskets too frequently and the rear disc brake failed to work in the wet),  and I then had a T160V Trident (gorgeous looking bike imo).  But that taught me first-hand what a tank slapper was ..and then one day it inexplicably dropped me on a roundabout.  I soon got rid of it and went back the Norton 850's  (..I had six of these over the years and used a Honda CB125 through the worst of winter weather).  From Norton I moved across to BMW's twins, triples and fours.

I have a copy of Bert Hopwood's book, and although it makes valid points - I found it whine on too much about his bosses.  He had issues not least because he was a pretty smart cookie, independent thinking and self-made man / engineer (from a poor family background) ..who often had to play second fiddle to Edward Turner.  Turner seemed to take (or was given in press releases) more than just his fair share of the credit, and he also had the ear of the big bosses, so Hopwood was all too often side-kicked.  

I was only there in the 70's as a punter, and then by the end of the 70's in design engineering within the West Midlands motor industry.  But in my opinion - between them, successive governments and politically driven Unions killed off every manufacturing industry in this country, and inbetween times their bickering and other 'circumstance' opened up opportunities which imported products took advantage of.     



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I would argue mods rode scooters as a fashion statement but I agree with the previous comment of the British bike industry churning out ever more outdated tosh.

Incidentally I own a 1949 James comet

Bfg I agree with some of your comments regarding the difficulties faced by the British bike industry but imo fundamentally the entire industry was backwards looking and entirely content to keep producing anachronistic designs.  Harley got away with it (only just in the 70s) with that peculiar American nationalism.

You do hit the nail on the head with the impact of the 750/4. Today it's hard to imagine how profound it was, maybe if Ferrari started selling road going f1 cars at Mondeo money could it be replicated. And that's why I think the BSA ohc twin in a cross the frame configuration as a pure sports bike was a missed opportunity,  the impact would of have been immense and a sign of looking to the future. Heck it might have even convinced ed Turner he couldn't keep making updates to the 30s speed twin and expect to remain in business forever

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12 hours ago, Bfg said:

A lot of sage things...

I agree the mods n rockers thing did harm to the bike industry and in particular the British bike industry - seen as big, oily, noisy and smelly (in any order). The Japanese bikes slipped under the net; whilst the press gnashed their teeth over troublesome bikers thousands upon thousands of Honda Cubs (clean, quiet, continent and odourless) slipped under the radar along with the 'nicest' people who rode them; some of whom would up-grade to larger Hondas.

The other aspect of the Japanese bike industry was their willingness to listen and change. Admittedly in the mid to late 60's the tyres, suspension, brakes and general handling could not compete with the Brits. People complained, the factories listened and within a decade Japanese bikes where almost on a par with their European competition (Brits almost gone by then). And then they continued to develop to the point where the Europeans had to up their game to catch the Japanese up.

Compare the above to the attitude of the management of the British industry as Flashbound says 'the entire industry was backwards looking and entirely content to keep producing anachronistic designs'.

Hopwood claims he saw the problems on the horizon but the management wouldn't listen. However he strikes me as a very 'challenging' person and I wonder if his open contempt of certain industry leaders got in the way of his message?


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As a student of Coventry Polytechnic in the 80s doing Manufacturing Engineering, on a course designed to churn out the cannon fodder of practical engineers to the West Midlands automotive industry, we had a few lecturers who had first hand experience of the British Bike industry.

DR. STUART Spraggett once gave us a scenario that he's been presented with at Triumph

So here's a design for a new 5 speed gearbox.  Please put together the manufacturing machines and tooling to make the parts and assemble them and test them. 

Great. How many are you going to make.

Ah, well we reckon we'll do it as an optional extra so maybe 5 a week. 


And then if it's successful, maybe 100 a week. 

Well that's a whole different number. 

Yes, and if people really like it we'll make it standard.


His point......fucking muppetry 

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Soichiro Honda - 'I want this engine to have a 5 speed gearbox as standard because that is what is needed for this particular model and the characteristics of the engine'.

And needless to say it would work slickly, with a light action and you would always be able to find neutral.

PS I'll stop now as I fear I might be hijacking this excellent thread.

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22 hours ago, Flashband said:

I would argue mods rode scooters as a fashion statement but I agree with the previous comment of the British bike industry churning out ever more outdated tosh.

Incidentally I own a 1949 James comet

Bfg I agree with some of your comments regarding the difficulties faced by the British bike industry but imo fundamentally the entire industry was backwards looking and entirely content to keep producing anachronistic designs.

The Mods and Rockers were much more than a fashion statement, it was a cultural clash of youth groups which (I speculate..) was very much about respect and territory, as many gang wars are.  Accordingly, the passion and violence was at times on a par with out of control soccer hooliganism.  On a street level it was intimidation (ton-up boys swooping upon scooter riders ..dangerously close and at reckless speeds), there were fights over where bikes were parked (inevitably causing damage) and which cafe's were home to which group,  and one to one attacks that one might more commonly associate with race discrimination. And then there were retaliations.    

Parliament shelled out for riot controls ..and even a sizable fleet of new bikes for the Police,  as that was the on-the-ground approach to dealing with the disturbances and £-thousands of damage being caused.  But even before most were deployed - the fighting suddenly stopped.  I am sure someone here knows why, but to many of us it was bewildering.  I heard there was intervention by members of the clergy who sat down with the groups leaders and acted as a mediator ..but I have no idea whether that is true.  The war was over but the image of 'bikers' was tarnished for best part of a decade.

As an aside, my brother later bought one of the 500cc speed-twins (in all black, without the bathtub, but with a tank rack) made for the Police - but never deployed with just a few hundred miles on its clock.  It was a very nice bike ..but rather tiny !

. . .

I also dispute "the previous comment of the British bike industry churning out ever more outdated tosh."  and "the entire industry was backwards looking and entirely content to keep producing anachronistic designs."     That imho is boolocks..  The aforementioned BSA Rocket-3 (..designed and running by 1965  if I recall)  and subsequently the Triumph T150 Trident were groundbreaking bikes - that out performed, handled and braked better than the Honda four. Indeed from my seat I'd say that it was Kawasaki's Z1 900cc which was to kick ass. 

But anyway, back to 1965 - 68, as far as I can make out it was the fart-headed financial management who were too scared to invest in anything that innovative (the BSA / Triumph triple) and to concede to its production.  But that doesn't detract from the bosses - who had the foresight back in 1961-2 to give the ideas a green light, and the designers and the development team the resources to actually get on with it.  But then they were held up at the starting post for three years.  It has been said that there was a lot of internal squabbling between the Triumph and BSA teams (..and so the two bikes had different barrels, cycle frame, and styling)  ..but I wonder how much of this was forward thinking and gearing up for different market places ?  ..&/or that the design had moved on in those years, with the possibly of marketing both three and four cylinder models which shared common parts ?  ..as was later done by BMW with their K-series (ignoring the obvious that BMW went for a laid flat configuration ..to align with their ever-popular twins).    Certainly a trip to the National motorcycle museum reveals many other innovations ..right to the end.  Four cylinder Triumphs, overhead cams, alternative front suspensions, water cooling, and a host of other 'brilliant for the time' innovations and styles.  Remember Craig Vetter's Hurricane anyone ? - which was offered by Triumph.  


And when the triple was given free reign - it was stunning on the race track (remember 'Slippery Sam').  But then so was Norton keeping ahead of the game with Paul Smart in the '69 TT (2nd place for a dealer entry !), the Gus Kuhn entries, and Peter Williams (works team) with the space-frame JPS Commando. Not to mention the isolastic engine mounts.

No., as a biker and as a design student and then design-engineer in the west midlands - I'd say those in the British bike industry were very much out there and looking ahead ..but were killed off by the bean counters and politicians.. who interfered by amalgamating companies (..that then lacked a general consensus to be led forward). 

Just image if the Japanese government had forcibly merged Honda, with Suzuki, Kawasaki, and Yamaha.  What do you think would have happened to their diverse motorcycle industry, not to mention the 'other lines' such as outboard motors, garden machinery, electronics, etc, etc.?    

The big difference was that most British manufacturing businesses (any and all industries) were dedicated to just one product range, and never could never raise the capital to diversify not to develop a truly global product.  Those businesses which made bicycles ..and then motorcycles ..and then cars - had to make a choice as to which (with their limited resources) they would pursue.   Conversely, it seems the big Japanese boys did one thing and made money, and then they saw and opportunity and branched out, and then they branched out again. They (or their community ?) were their own bank.   And when any particular market was in a slump it was honourably supported by the other divisions ..rather than being sold off.  

Sir Bernard Docker (BSA Chairman) had the foresight and leadership to do this with BSA (arms and munitions, bicycles, motorcycles, cars, commercial vehicles, and goodness knows how many engineering companies supplying all sorts of things to everyone else).  But when the leader gets old  &/or is ousted, then things fall apart.  That still doesn't detract from the outstanding achievements of the teams of men (and women) who had the enthusiasm, the passion, the self motivation, the foresight and the ideas.  It's just that they ..and their innovative work, were shelved.

Men in grey suits rule. 

. . imo.



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If it was anything like their car industry, the Japanese bike manufacturers would have had significant government support, export credits, low-interest loans from local banks with a nod from the ministry etc.

I believe Honda was the exception, as Sochiro ignored the Japanese government’s request that he not enter car manufacturing (they were trying to consolidate the eight or so companies already making cars in the early 1960s) and by the mid 60s Honda was such a money-making machine he didn’t need any govt help anyway. 

The engineering skill and resilience of Honda was just immense - their first volume car, the 1300, was a complete flop but the lessons learnt  from the failure (the air-cooled engine was a major issue) and drive to just ‘get on with it’ meant the Civic was launched less than three years later, a completely new car with a completely new engine. 

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Bfg if I've hit a nerve I apologise and before I go any further I would like to say I have enjoyed your thread hugely and share your pain 're shoddy work done by 'professionals'

Re mods and rockers, you were there by the sound of it. I wasn't so I defer to your judgement. 

Good luck with resto but we disagree fundamentally on the brit bike industry. Viva la difference and once again good look with the resto


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The triples were a load of old cobblers; carefully assembled by craftsmen they could give japanese in line 4s a run for their money but when assembled by disaffected brummies waiting for the next strike to happen were a leaky unreliable disaster. Vertically split crankcases for a triple? Stupid decision by bean counters. Any 4 cyl that BSA/Triumph might have bodged together on a similar basis would likely have suffered similarly. Like the aero, shipbuilding, motorcar and many other industries that the UK was a player in post-war there were very talented designers and engineers working in the motorcycle trade doing great work, but all too often they were hobbled by having no budget or by being asked to produce the moon on a stick.

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On 3/4/2020 at 11:19 PM, Flashband said:

Bfg if I've hit a nerve I apologise and before I go any further I would like to say I have enjoyed your thread hugely and share your pain 're shoddy work done by 'professionals'

Re mods and rockers, you were there by the sound of it. I wasn't so I defer to your judgement. 

Good luck with resto but we disagree fundamentally on the brit bike industry. Viva la difference and once again good luck with the resto

Thanks, and otherwise "no worries mate" as the Aussies seem fond of saying.. you didn't hit a raw nerve,  but as a retired design-engineer I have indeed been frustrated by bean-counters and political decisions over-ruling good industry knowledge, backed up by solid market research, and innovative design.  It's true that I'm very saddened to see what has become of manufacturing (in all industries) in this country (both my grandfathers were in engineering / manufacturing as was my father) and am at a loss to think what skilled jobs will be available in this country within the next 20 years. Certainly very few would be interesting careers from my point of view ..but then I'm a soon to be extinct dinosaur.

Our disagreeing is fine, as we come from a different perspective, and the differences are all part of a good conversation between friends. 

I do retain a great respect and brand loyalty to Honda, and although I've never owned one of their cars - I only buy a Honda powered lawn mower, generator, or small bike.  The outboard motor on my boat happens to be a 9.9hp Yamaha long shaft, and I don't see a better motor out there for my purpose. imo it's great.  I need to buy an outboard for the boat's tender and would only consider a Honda or Yamaha.  I don't hate Jap bikes, I just don't like them as much as I do British or German ones.

Neither Triumph I owned leaked, likewise a friend I rode with who rode the T150 Trident. They always started easily, were quick and reliable and we never had electrical issues or anything else ..save the head-gasket problem on my 140 ..which was most likely due to its big Avon touring fairing buggering up the air flow.  My T160 Trident had handling faults which I couldn't accept, but perhaps if I'd taken the bike to a specialist they might have found something simple that was out of adjustment. As it was, I lost confidence in the bike and so got rid of it.  Likewise my Nortons were maintained to be oil tight. 

True - many aspects of British bike design was not very clever,  but I suspect more issues arose because home and self-taught mechanics thought they could take shortcuts and never use things like a torque wrench or a specific tool, and then resorted to reuse gaskets.  Conversely, Japanese super-bikes were not designed to be worked on by the home mechanic. Everyday maintenance aside, I'd expect a main-dealer's trained mechanic with good quality tools to be better put a bike back together better than the average Jack working on his bike under a lamp post in a side street.


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Ok.,  here's a little more progress the engines I'm working on. .

Engines in plural because I presently have three Sunbeams ;  Katie  is the 1948 'early' S7,  and then I have the sister bikes of 'Nudge' ..the skinny wheeled S8 (formerly my daily rider)  & 'Pudge' ..the fat tyred S7-deluxe. Each were registered NXN from the same borough of London - Pudge on the day after the Coronation, and Nudge some  five weeks later. Both were finished in mono-chromatic silver. However at present neither bike is on the road, and each engine is in bits.  Nudge's engine has the correct / original (# S8 11660) for that frame,  but Pudge's engine  is # S8-3178, which suggests it's from a 1948 bike.  (from 1948 all the engines had an S8 prefix even when fitted to the S7-deluxe).  I do have a spare engine but that's from a slightly later bike (c.1954) so there's really no point in my using that ..as its number will still not match.  

As discussed (back on page 2 of this thread) Pudge's cylinder head was discarded because its cooling fins had been butchered. So I substituted that with the best condition cylinder head I had on the shelf (..that is the one I showed being reworked in March 2017).  However although the cylinder head numbers are not in accurate sequence nor are they recorded with the the engine number - their numbers are generally within a few hundred of the engine block number.  And this one (#11107) wasn't.  Nudge's original cylinder head ended up on Hovis, the 1955 S8 I sold last year, whose engine I had borrowed to use in Nudge ..my daily rider.  When that engine was refitted into Hovis I didn't bother to swap the head back.  I had a good 'spare' but that number is 3072.

So I now have the original block for Nudge, but whose cooling fins have also been butchered.  So I don't know whether to reuse that in a nice bike.  And I have an 1948 engine block (in nice condition) whose cylinder sleeve had been replaced ..but not sealed.!  That issue I now hope has been sorted with the aid of Loctite wicking bearing lock.  And then I have two cylinders heads, one from a 1953 bike and the other from a 1948 bike.  The annoyance is that I had reworked the later head for the early engine block.!  This all comes down to my having done this two years ago when I used the best of what I had available at that time.  But now they are both in bits - I've decided to put the later head on the later block and the early head on the early block.  I'm sure it makes no practical difference and the cylinder heads are supposed to be the same. However I will know.  

Are there any differences ?  . . . yes but as far as I can tell those differences are superficial. 


^ the older (c.1948) cylinder head (top) in comparison with the c.1953 cylinder head (bottom). The difference seen is in the casting shape of where the head gasket sits.  On the older one the casting shape curves much closer around the studs. As the head gasket is exactly the same, it really makes no difference.  Another change is in the rear right-hand bolt hole (..next to the timing chain chimney). It's not clear to see from this angle but the height of the boss, which the stud bolts through, is 1-1/8"on the early head, but only 3/4" high on the later one.  Naturally stud length will have to be matched to those.

That seems a retrograde change as I have heard of these bosses cracking when over tightened. I might only imagine that it was a change to help in production, because in all otherwise important aspect such as porting, combustion chamber shape, spark plug position, etc,  all seem to be very similar. 

NB. Katie's / the 'early' S7 cylinder head was different to these in many respects. The spark plug position within the combustion chamber was for example different, as is the stud pattern, as is the camshaft and rockers. 

Anyways up.. I've made the decision to use the cylinder heads in close accordance with the engine blocks numbers.  So  ;  Pudge engine # S8-3178 will now have cylinder head # 3072  and  Nudge's engine # S8-11660 with cylinder head # 11107.   I'll not mix components within each block, nor within each cylinder head ..they'll all go back in where they came out.  But I have two engines to rebuild, so set about getting the parts ready.


^ the early # cylinder head as it was from sitting in store.  I had bought it together with a job lot of garage clearance bits, and done a drain-down test on this a couple of years ago ..so knew the valves needed re-grinding, but otherwise it appears to be a good condition item.   The original design of breather on these engines was stupid. It breathed out of the rocker cover and the fumes / mist / humidity was to the open air at the front of the engine. Of course this ran down the front face and was then blown back along the cooling fins, which being hot baked the oil residue on.!    One of the first mods many owners do is to buy a catch box from Stewart engineering (Sunbeam specialists) which a drain pipe fits to ..to take any mist down to under the engine. 


^ camshaft looks in serviceable condition.. I'll clean, inspect and measure that at some point to see if it still looks good. 


^ inside wasn't very clean.


parts cleaner and power wire brush made a good start, but as you can see cleaning up inbetween the cooling fins had limited success. 

I had to resort to chemical cleaner (acid) to improve this. . .


That's better.  I used what's known as 'de-carb'  short for de-carbon, which outside industrial use is sold as oven cleaner. And it literally dissolves carbon, which of course includes burnt on oils, but also is a viscous acid that dissolves carbon based things like skin, finger nails, hair, eyes, bone ..so  USE with GREAT CAUTION !

The de-carb also slowly attacks the aluminium, and leaves dull grey patches. After a good scrub down in water to get rid of most of the acid (I used a jet-wash, close up and at full power) the discolouration can be cleaned off with wire brush &/or scouring pads with engine cleaner.  It's perhaps not as pleasing a finish as bead-blasting - but for a single engine component it is much more convenient to diy it,  than to back n' forth to someone who has the facilities.  And after a few weeks on the road they'll not be much difference in the look of various engine parts. 

NB. that casting number seen in the rear corner is not on the later cylinder heads.    


Then I had something to work with, and could see what needed to be done.  I used a hand file to smooth out any dents and I used a Dremel to rework the combustion chambers.  . . 


^ the valves are so very close to the combustion chamber side walls, that even when open - the gas flow passed them has a very restricted route.  The job I'm doing here is to undercut the gasket face so the gasses have a greater width to get through.

I did this and detailed what I was doing before, so I'll not repeat it all again. But for anyone looking afresh  < here  > is a link to that work.  

This time around was easier because I had the previous cylinder head sitting beside me as a pattern and to measure from.

In summary though.,


^ this shows a 2.5mm dia drill-bit, which I'm using as a width gauge to assess the amount of extra clearance the undercut is giving (with the valve open).  Before my re-work that drill bit didn't fit into the gap.  As you might see I've increased the width of the gas-flow route by 1.5 - 2mm. That may not seem a whole lot but as a 60-80% increase over the original gap of 2.5mm - it's significant ..and I've not touched the gasket face.  And as the advert says "every little bit helps".


^ likewise this photo shows a 5.5mm drill bit being used as a indicative gauge  ..which before I undercut the sides was a tight fit in that gap. So the clearance is now almost twice as wide as it was, and this runs about a quarter the way around the valve head perimeter. So again a significant improvement for the gas flow. 

The amount I've removed around the tight spot of each valve is similar, simply to aid the flow of gasses - both into and out of the combustion chamber.  Easier means less resistance, and hopefully more gasses moved in each fraction of a second. Inlet wise that equates to more fuel in the chamber so a subsequently slightly bigger bang.!  That's the basic theory ..although port and combustion chamber shapes, and the flow of gasses around the valve guides, the swirl effect within the cylinder, as well as valve timing and back pressures all complicate the exactness of the science.

Without changing the carburettor, simply getting the fuel mix through the cylinder head inlet port is the next thing I address. . .


 The black line has been marked from the carburettor's insulator / gasket. The port into the cylinder head is a restriction, in this case by about 1mm all the way around but further in was also angled towards the rear cylinder.  That restriction might be likened to using a 21mm diameter carburettor in place of the standard 24mm one.  So the object here is to let the standard carburettor do its job, and then again to allow an unrestricted (but not larger) route for that fuel-mix into the combustion chamber.


The insulator block is standard, and the restriction within the casting is apparent despite the amount of aluminium I've already cut out.  Again I must emphasis that I am not changing to a larger carburettor, nor do I want the inlet tract to be any bigger than necessary ..because a greater cross sectional area would decreases speed of flow. All I'm doing here is getting rid of the restriction.


^ I simply use an appropriate size of penny-washer to gauge what I cut away. I'd like to think it's pretty accurate. 


^ once I was happy with the size and shape I polished the inlet port, to minimize surface turbulence.  However I don't bother to rework the exhaust ports on these engines because they are already massive (not at all restrictive) and any polishing would soon have a layer of soot over them anyway.

Subsequent to doing this I cleaned out rough lumps of casting within the fins, and cut away the timing chain tunnel where again a loose chain had worn groves in it, and generally tidied the casting up, redressed gasket faces, etc, again much the same as previously discussed on page 2 of this thread. 

I then ground in the valves  . .


Ok so I cheat.. but time is time whether you're at work or whether you're retired.  I use the cordless drill on the valve stem and gently pull the spinning / grinding valve onto its seat.  Like doing it by hand - I use a touch n' go action rather than just spinning.   Again I used coarse and then fine grinding paste, and then just a little more with no paste at all. 

So finally..


With the valve's temporarily refitted, and the cylinder head put aside where it will not be disturbed, and leveled. each combustion chamber is filled with parts cleaner. Any fluid which leaks passed a valve will be seen in the ports.  If there' fluid in the inlet port then there's a possibility of either valve leaking but which fluid level goes down indicates where it came from. After 12 hours it ought to be obvious which need a little more regrinding.  On this cylinder I had to redo #1 cylinder's exhaust port. No problem and much better to find out now than after I had put the engine together and found it low on compression.  

So that's it for today.  Hope it's been of some interest and not too boring or long winded. 

Any questions or comments, do please - feel free to contribute.

Have a good weekend, Pete.

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OK a quick update and then I'm back out to the garage..

As said above - I'm working on the two engines from my 1953 Sunbeam S7-deluxe and S8 sister bikes, and that I'd just reworked (combustion chamber and a little porting) the older cylinder head, which is to go with Pudge.  Well over the last couple of days I've been playing catch up with the later cylinder head, essentially cleaning it up for reassembly.   In brief, this is what's what. 


^ although not in too filthy a state, particularly on the outside, there was still a lot of burnt-on / oil staining which while I rather-like not to have.  So I again used de-carb to scrub it out and then the power wash to blast it,  before more scrubbing with scouring pads and degreaser, and the rotary wire brushes on the cordless drill. The gasket faces were also cleaned and checked (..as I don't like a leaky engine).


I striped the rocker shaft and individually cleaned each component, and checked it for wear, any signs of damage, and for gunged-up oilways.  The rocker-arm forgings look pretty crude, and massively overweight by today's standards, but for a 1950's motorcycle which I'll not be entering in the TT - they'll do fine just as they are. 


^ although the rocker shaft and bushes were in surprising good condition and well within wear tolerance, I noted this rocker arm's bush was a little loose.  Worryingly, if these bushes turn in their arm - then the oil feed holes turn out of alignment ..and the oil feed directed to the cam lobe is prevented.  So although this was not turning, I took the precaution of pressing it out (using the vice and a suitably sized socket as a drift) then liberally covered it in Loctite and pushed it back in again.


The hole was very close but I checked each one anyway with the correct size drill bit - just to ensure that non are slightly misaligned or otherwise have a layer of crud in them.  The drill bit illustrates how the jet of oil from this drilling is directed at the camshaft.  NB. This 1944 (designed) motorcycle engine has alloy block, cylinder head & cases, and is indeed OHC. 


I had ground in the valves previously and again recently checked them (via a drain-down test over 48 hours) and their seating was good.  Subsequent to its disassembly and cleaning - I liberally oiled the pushrod tubes and reassembled the valves.   ^ here I'm just quickly running around with the die to ensure all the threads are clean and free running (cylinder head is on its side, but still I'm careful that no bits fall inside). 


I have a brand new camshaft and a good used one to fit into these engines.


^  visually one can see the new camshaft lobe is shaped for a longer open duration.  The inlet valve lifts are ~ 0.295"  and  0.311 for the old and new camshafts respectively.   It will be interesting to see if I can feel any seat-of-the-pants difference in performance.  I'll put the new camshaft into the heavier of the two bikes.


Again after checking the oil ways within the the camshaft are thoroughly cleaned out ..and likewise within the cylinder head (there are no external oil pipes with banjos on this engine, all the oil ways are internal) - the camshaft was liberally lubricated and refitted.   Pretty neat design layout don't you think.  

The pressurised oil route is from gear pump in the crankcase, up via a drilling to the camshaft's rear bearing, then through the camshaft itself to its front bearing. From there the oil is routed up through that fat stud (..front on the cylinder head / left) to the rocker shaft's pedestal (see below).  And then through the rocker-shaft to each rocker arm, lubricating each bearing in turn and pumping a squirt of oil over each cam lobe.  Thereafter gravity returns the oil to the wet sump via the timing-chain chimney at the back of the engine. This oil wash takes with it heat from the rear cylinder.    


^ an oil splash plate covers the camshaft, even within the rocker cover. 


^ Camshaft & rocker assembly reinstalled. I'll now go around and loosely assembly all the nuts n' washers to check they are all present and correct. 

So that's progress to date ..with this, the later cylinder-head now close to being ready to refit. Today I hope to do the same with the earlier cylinder head - so they'll be both to the same stage.    

Have a good weekend.   Pete.

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Yesterday, I was doing much the same with the earlier cylinder head (I'll be using in Pudge) as I had done previously (above).  Indeed most of the tasks were the same ..but I had a few other things to do with this one. . .


^ The rocker-arm shaft is hollow ..to feed engine oil under pressure to the rocker arms.  These arms are so drilled to intermittently squirt oil onto each camshaft lobe.  However, I noted that the holes in this shaft were particularly blocked up with crud/ hardened dry dirty oil.    I use a  2.5mm drill bit to clean them out and even then this drill is a loose fit ..so very likely they were originally drilled at 7/64" (2.78mm).  However these little holes* were clogged to such a degree that even a 2mm drill bit wouldn't push through by hand.  The area of a circle is  PI x r2  ..which means that each hole aperture should be 6mm2.   However, restricted as these were - the hole's cross sectional area was only 3.14mm2 .. so just a little over half its correct size. 

Naturally, if the camshaft is to be lubricated as intended / as designed - these holes do need to be cleaned out, and also the inside of the tube needs to be clear.  Access to inside the tube is via a screw plug in one end. Oddly that was not at all tight.  Not good because if oil leaks passed this - then oil pressure to lubricate the camshaft is less. If the screw were to fall out then there would be no oil to the camshaft at all and a sizeable screw floating around inside the engine to chew thing up.!  So after cleaning the shaft's inside gallery - I refitted its end plug with Loctite.

Btw.,  the scoring you see in the above photos looks very much worse than it feels or measures. The rocker arm bushes fit is within tolerance.


Next little job was the dowel which locates the timing chain sprocket in correct orientation to the camshaft . .


^ The timing chain sprocket loosely fitted - to show where the dowel locates into the end of the camshaft.  The following shows that sprocket off and its through-drilled dowel.


The problem with these is that they are through drilled ..so the dowel can get pushed out.  The shouldered bolt which fastens this sprocket is supposed to ensure it is secure, but still., once pushed through it becomes loose. A spot of weld on the back face fixes that.  Only a one minute job to do, but five minutes needed to get the welder out and then another five to put it away again !


^ cleaning parts and ensuring the oil ways are clear is just part of the task, close inspection of every tiny part is needed. As you can see this tappet adjuster lock-nut is cracked in several places around its perimeter. (NB. This was face down against the rocker arm so the cracks were not visible without dismantling and cleaning).  In time this lock-nut would have split right through and possibly broken in two.. Would those lumps of steel have then been washed or vibrated into where the camshaft is spinning ! ? 

Next task was the rocker arm's contact pads. Being an overhead camshaft these bear directly on the camshaft lobes (ie., there are no cam followers). .


Rocker arms 1 - 4 (left to right).  The first two are as they were.  You can see coarse groves and the flat with hard edge from wear ..which at one time was smoothly curved.  The third one I'm in the process of regrinding, and the fourth has then also been smoothed down to 1000 grit.   These are not hardened faces, so I can regrind them by hand.  The first cut is with a power file directly across that lower hard edge.  The object is to restore a curved shape but to ensure the contact pad remains square (rather than introducing a twist in its surface) ..so care is needed (especially when using a hand-held power tool).  Thereafter I used sharpening oil-stones, laid flat on the bench as I worked the rocker's pad over it (coarse and then fine stones) to smoothly curve the surface plane and to cut away the wear ridges.  I then used the power file again to round either side (so there's no hard side corners to cut into the camshaft lobe) before working through grades of emery paper.  Thereafter the contact pad faces were polished (below). .


^ looking as if those contact pad faces had been chromed  B)

Naturally they are not perfect ..but certainly are much better than they were, where their hard ridges would soon have worn into the camshaft lobes.



^ A number of studs needed to be removed and refitted. One needed to be replaced, and most needed their threads cleaning so the nuts would run all the way down the threads.  Mostly invisible - but the valve's guides, the camshaft and rocker arm parts were each liberally coated with engine oil throughout reassembly.  The one tappet adjuster lock-nut still needs replacing (others were all fine),  but otherwise this cylinder head is also close to being ready for refit. 

For the eagle eyed.. the safety pin is there as a reminder that the nut is deliberately loose.  The reason is that I'll take it off again (once the head is fitted onto the block) so that I can back-fill the oil way through the camshaft with engine oil.

That's it for yesterday's tasks..  so now it's time for me to do some more..

Catch you later,  Pete.    


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That splash guard thingy between the rockers is interesting. Not seen anything like that before.

With the work on the cam-end of the rockers, do you check the contact with the cam with blue or something? This design rather relies upon the cam face, rocker axis and rocker pad all being quite parallel.

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^ the guard ensures most of the ohc oil-splash stays within the confines of that cam-shaft housing, before it runs down and drains back to the sump,  but because the crankcase breather valves are situated in  the front face of the rocker cover - it also serves as baffle to the crankcase oil-mist.

The reshaping of the contact pads of the rocker arms I did by eye and feel ..using the lesser worn areas of this face as a guide to keep things true.


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yesterday afternoon I made the decision to try and clean Nudge's crankcase up to see if I might reuse it, and thereby retain the original engine number. . 


^ poor thing has been abused by some previous owner who "thought" they might prise off a tight cylinder head ..by locally levering their screwdriver against a cast aluminium cooling fin that's only 1/8" thick.!   Very likely the cylinder head was 'tight' because the inner stud's nut hadn't been undone (seen here inbetween the timing chain chimney and the rear cylinder). Admittedly it is not easily seen from the outside of the engine, even when the inspection cover is removed, so unless one looks at the manual - then its easy to miss.  


The engine was stripped perhaps six years ago because the head came off the top of a big end bolt.  I felt the vibration and investigated what the issue might be before it threw the rod ..so I was darn lucky that no damage was done.   At that time I was working long hours and so I simply used another engine in this, my commuter, bike.

So, to get on with things I spent quite a few hours simply cleaning up dents, chips and other signs of its hard life.  In fact this engine casting is about as bad as I've seen (and I have worked on a lot of these bikes).  I'm not talking about abuse here so much as the casting reflects a set of moulds which were at they end of their production life, or else this was cast on a Friday afternoon near close of shift.


This oil filler / dip stick tube doesn't reflect the evenness of sand casting that's normally a feature of these engines ..In fact it's just plain ugly. 


Around the drilled and tapped hole (for the chain tensioner) are other examples of defects cast into this case.  Above the clip is not a crack in the casting, its simply where the sand casting (mould) had started to crumble. 

I exaggerate not when I say - I spent over three hours going around this casting a little more presentable.  And while doing so - I was pondering on whether I should leave such casting faults as 'original' or to try and correct them.? 


^ Like the cylinder head.. the block's timing chain chimney had deep score marks from where its chain had been running very slack.  I can only imagine when listening this engine run ..the phrase "oh., they are all like that sir"  came to mind ! 

And then I acid cleaned the block (using de-carb) inside and out, and  jet washed it, and then scrubbed it again with scouring pads.


^ Still wet from being scrubbed.  On the face of it, after eight hours work, even I could barely tell the difference.!   Mind you., as I do things I tend to forget exactly what they were like beforehand.  The fins do look pretty straight now and the casting in general is perhaps a little more true the design. The acid matted the shiny surfaces and edges I had filed smoother and/or otherwise trued up.     

Some owners polish the flat areas inbetween the fins, which is not original ..but if the case is a good shape it can look very pretty.  Personally I prefer the finish of coarse grit blasting (not sand), so then it is an even mat finish all over.  But for a road bike this will do.

And then today I sought to address the broken cooling fins. . .


I don't have aluminium welding equipment and even though I bought high temperature gas blow-torch ..and low temperature aluminium rods - my prior attempts (on another engine) were less than 100% successful ..I guess because the whole darn thing is a heat sink and so I just couldn't get it up to temperature.  So here I'm attempting a simply cosmetic repair which involves Araldite and aluminium powder (saved after grinding the cylinder-head's combustion chambers). . .




^ aside from the colour difference.. with care it can be made to look half decent, but the reality when working with Araldite is that it's a very sticky yet floppy consistency. The aluminium powder helps but still it takes a bit of dancing around to get it in the right place just as it sets.



^ dusting over with aluminium power helps achieve the final  'cast finish' result.


I know of engines which have had bits of broken off fins stuck back on ..with Araldite,  but I've never tried this aluminium powder filler mix before.  Time will tell if the heat / expansion / contraction of the aluminium, or indeed and engine's vibration causes these repair to break off again.  If it does ..well not all is lost - I can always clean them up again., and then have the fins professionally welded. 

That's it for today. Just an hour of work done but possibly more of a noticeable result than all of yesterday's long day.

Best regards, Pete.

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..subsequently learnt of this . . 


Araldite® EP 300 A/B Adhesive is an extrudable, two-component, room temperature curing epoxy adhesive designed for service temperatures up to 400°F (204°C). This product is suitable for bonding a wide variety of materials such as metals, composites and many other dissimilar substrates.

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I've mainly been doing other stuff this week so just a little to update..


^ A bachelor's home..  Mine has elements reminiscent of a production line.

The two  engine blocks of the engine's I'm rebuilding.  Both I've tidied up in regard to filing the cooling fins and around the edges to diminish the appearance of knocks and scrapes incurred over the past 67 years, as well as some pretty awful original casting blights on the later case.  The other / older one (to the right) was professional bead blasted, and will be used in Pudge ..the S7-deluxe Coronation window-display bike.  The original to Nudge block - is the one I chemically cleaned and then used a scouring pad and degreaser on, and then last weekend - cosmetically disguised its broken top fin.  Now there's not nearly the visual difference as it may appear here ..due to uneven lighting. 


^ what I'm doing here is sorting / checking I have the components for each engine, along with all the correct fastenings and gaskets etc.  It may seem obvious to keep all one bike's bits together, which on the whole has happened but these engines have been dismantled for quite a time now, and Pudge's was dismantled by someone else (..page 2 of this thread), and subsequently each box has been rummaged through looking for bits from Hovis which I sold in April springtime last year (page 4 of the is thread).

The paper-type  Oil filter is not standard, but is another little conversion I like to do on my own Sunbeams.  I have to convert Nudge's engine yet so I'll come back and share details of that modification in a week or two.


^ Timing chains. The top of the three shown is a new one which illustrates how little it flexes sideways (no wear in its pins or links).  The middle one is just slightly worn, and the bottom one is plainly just worn out.  

So there you go, as I say not a lot to report on this week, but enough "little steps at time"  in the right direct ..and progress will finally be made. 

Wishing each and all of you a good weekend,


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Good afternoon all.  With so many other distractions, not much has been happening on the bench this week ..but here's a little conversion I do to the oil filtration on my old Sunbeam motorcycle engines. . .


^ The engine block (in aluminium) with the original filter ..the oval shaped brass top with gauze mesh around it, soldered onto a base plate. This plate (when inverted so the filter is facing downwards) is sandwiched (hence two gaskets) between the block and the cast aluminium sump (top right).  The plate has a few through-holes, but they are not so large because it also serves as a baffle between the turbulence in the crankcase (with the crankshaft spinning around) and the wet-sump oil reservoir. It would helps stop the oil in the sump from surging forward ..away from the oil pump's pick-up pipe, under heavy braking.  'heavy' being a relative term with 1940's drum brakes,  but perhaps the oil surging sideways is also a matter for concern when the bikes are used with a sidecar.

To the left is a (HOF306) disposable paper element oil filter ..which I now use, along with viton o-rings.  Seen at the bottom of the photo is a spacer made and supplied Stewart Engineering, who are the primary supplier of post-war Sunbeam parts ..and I believe owners of the Sunbeam Motorcycle name and its design copyright. The 'sump spacer' is supplied with new gaskets and  x12 longer studs. It cost the best part of £100 + p&p  ..but is (sort of ) useful because it increases the standard (3-1/2 pints) engine oil capacity by an additional pint.

However, the spacer fits between the baffle plate and sump casting, so unless one extends the pick-up pipe, that extra pint of oil just sits in the bottom of the sump. True it does general mix in with the oil being circulated - but it does NOT add to the oil capacity that is accessible to the pump.   So, should the oil run low, the pump will still suck air (despite still having that extra pint in the sump).

Why is the spacer not fitted lower ..between the spacer and the sump casting then ?  Well, without extending its pick-up pipe down to the bottom - the pump would suck air at the same oil level.  The gauze filter has a soldered-on collar to snugly fit around the pick-up pipe. This is not insurmountable but it would need to be removed for an extension tube to fit through it.  More the question is - how well would the baffle plate work with so much engine oil above it ?  I suspect that oil would literally be driven up the walls by the turbulence within the tight confines of this crankcase.   So., I change things.  I leave the baffle plate where it was designed to be but I extend the oil pump's pick-up pipe.


^ This shows the standard oil pump's pick-up pipe relative to the inside of the sump  ..this is without two thick sump gaskets, the filter/baffle plate, or the after-market sump spacer.  There is about 1/4" between it and the bottom, but because of the notch in that pipe - the pump would suck air if the oil locally surged away to be less than 1/2" deep.

" Well that's a ridiculous low level of oil " you might rightly say.  But let's do the maths (on these little engines). We'll start with a (standard) full capacity of 3-1/2 pints, and then there's,  let's say, 3/4  pint of oil needed to fill the oil-ways, cavities and galleries throughout the engine,  and then when the engine is running there's another 3/4 pint being splashed against / running down the insides of the cylinder head, rocker cover, timing case and crankcase.  And the 1/2" air-gap between the sump and the top of the notch in the pick up pint constitutes another 3/4 pint, so also does the distance between the top of dipstick mark to the bottom mark (ie., conceivably less another 3/4 pint).  So we have 3-1/2 pints,  less 3/4,  less 3/4,  less another 3/4, and less yet another 3/4 pint = 1/2 pint reserve !   Is it not feasible that this (= just 3/8" deep) might surge under braking or when a sidecar bike turns quickly through a fast corner ?  


^  illustrating the crankcase, and sump, relative to the length of the oil-pump's pick up pipe with the sump spacer fitted.  The shiny tube I'm holding up to it  is a length of aluminium which I'll use to extend the pipe by the spacer's thickness (21mm). 


^ The aluminum tube I use is an interference fit, on which I use Loctite but then literally hammer it on.


^ With the sump spacer in place, but still without x2 thick gaskets and the filter/baffle plate, I've reduced the clearance between the sump and the tube to about 1/8".


^ I then cut the bottom at a 45 deg angle so there's no restriction to oil flow, even if the tube should happen to work loose and drop down.


^ The pipe is now cut, de-burred and thoroughly cleaned out,  and I'm fitting the new / longer studs.

. . .

Moving on to the engine oil filter itself.. whose casing would stop my extended pick up pipe reaching the bottom,  and otherwise has too coarse a mesh to prevent fine contaminates (byproducts of combustion and running-in engine wear) from circulating. . .  


^ the solder around the front of this one happened to be cracked anyway.  


^ Blowtorch used to un-solder it.  I leave the two anti-surge plates in situ.


^ cleaning off the surplus - it's surprising how the weight of this adds up.


^ Ok cleaning up job done.  two new holes (red arrows) have been drilled and I'm just about to add a piece of aluminium angle - longitudinally to the top face of the plate.  This is to stiffen the plate against panting ..in a small crankcase which changes in volume by 500cc with every half revolution, and might also help with lessening the amount of oil being driven up the inside walls of the crankcase by the turbulence from the spinning crankshaft.

P1340112s.jpg.98533e4feaed1626f1d05122193315bc.jpg .

^ Here I'm checking a length of rubber hose I've cut to sit between the crankcase and the baffle plate. It effectively seals around the hole through the plate and acts as a spacer to (again) prevent that plate from panting. 


^ Working on two engines at once.  That on the left shows the extend pick-up pipe with rubber hose sleeve around it. And the engine to the right shows the sump spacer in place and illustrates how the disposable filter fits. (NB. old sump gaskets are only used for dry assembly trials, and not for the final build).   A fair bit of filing was done to have the plate and the sump extension sit down on the studs, as those (although original) are not perfectly parallel.  


^ detail showing my extended oil-pump pick-up pipe inside the disposable filter.  The cast finish on the inside of the sump (seen in first photo) has been locally smoothed, so the o-ring forms a seal between it and filter, which is sandwiched in there.  The baffle plate is of plated steel - so I'll also place a strong magnet on it. Because of it's size and shape, it can't go anywhere but in practice I've also never known one move about.   


^ The sump loosely dry fitted in place.  And unfortunately yes, the sump does have to be removed to change that filter, but so did it when needing to clean the original gauze.  Once after 200 miles of running in and thereafter every 3000 miles is not such an issue with a wet sump design. And of course, the oil itself may be changed frequently without dropping the sump. 


^ viewed of the aperture for the rear bearing carrier ..which also carries the oil pump and oil way galleries. The hole between the two studs at the bottom of this flange face is where the oil pump draws the engine oil from the sump, via the pick up pipe.  And the hole through the flange near the top is where the oil-pump sends the pressurised engine oil up to the camshaft.     Inside the case you can just see the upstanding length of aluminium angle used to stiffen the sump's baffle plate and to hamper oil being driven up the inside wall of the crankcase.

In this morning's post I received a second sump spacer from Stewart Engineering, for the other engine. . .

P1340120s.jpg.642826838d7b715c1845214349e45edf.jpg .

^ Actually it's a nice casting, but their instructions neglect to say it needs finishing.  It's a raw casting and so the gasket faces are not smooth, and more often than not these castings are not flat ..but is often slightly bowed &/or twisted - so it needs flattening on both sides before it will be oil tight.  Often the holes need easing too, but that's because these Sunbeam engines were made on 'very tired' war-time machines. 

Personally I also find they look slab-sided when fitted - and so, as you see in the other photos,  I file a grove all around it's outside, which (visually) halves its height and imo compliments the lines of crankcase cooling fins.

That's it for today - it's time for me to do some flatting and filing !

Best regards and take care,



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This afternoon I carried on from the above  ..catching up on the second engine. . .


^ the problem with studs is that if any of their holes have been drilled off-perpendicular to the gasket face  then the stud either splays sideways or in or out ..relative to the others, so then the drilled castings of the sump &/or sump spacer wont slide over them. Of course the longer they are.. the more out of true alignment their free ends are.  Mostly this can be corrected by judicious filing of the holes in the sump and sump extension . . . 


^ The red felt pen ticks indicate where the stud fouls in the hole, in this case - preventing the sump spacer from going on.  So here (in this photo) I'm using sideways force on the drill bit to ease the hole in the direction of the tick.  These sump spacers have slightly oversized holes., but even so they needed filing or in my case drilling sideways to make it fit.  The cast sump I'm using was not original to this engine, and its drilled holes were a tighter fit to the studs, so a time consuming amount of rework was needed. . 


^ this particular stud's hole was drilled and tapped at a slightly wrong angle, whereby the free end  of the stud out of alignment by perhaps over 1/16".  After fitting and marking which way it fitted in the hole - I took it out again and bent it !  


This is that same stud, now refitted. You can just about see how its bent (its shape sprung back some after being altered in the vice).  The end tip of the thread is now in alignment with the others, but of course it is still bowed out, but by only half as much as its end previously was !


^ It took me a couple of hours to alter the spacer's and sump's holes to fit these crankcase studs. Even now some are an interference fit - but those parts can be wiggled off ..by hand rather than needing wedges to free them.  Once in place there's just a little slack on the studs - so the crankcase's holes were all drilled in the right place ..just not at the right angle.  

That part of the job is now done, but to my eye the spacer looks slab-sided and so ugly,  relative to these otherwise beautiful crankcases. . .


^ pencil marked to be cosmetically altered  . .


^ carefully done all the way around,  except in the area of the sump's drain plug  ..and I do this simply to know which way around the spacer is orientated.  If fitted the other way around - my filing to suit the stud pattern doesn't work and the sump itself won't align so neatly with this spacer ..as its holes have been drilled just little towards one end. 


^ widening that hacksaw blade cut with the corner of the file to form a v-shape groove.


^ and then rounding that v-shape groove into a shallow U shape.  The finish isn't critical, but any neater and it looks worse !  ..because the castings of the engines cooling fins are never perfectly straight nor smooth.  


^ that's it.  A whole lot of work to file a shallow grove approximately midway down the slab face of the spacer.  The proportions are reasonably compliment to the spacing of the engine case cooling fins ..and so after a few months on the road (when all the aluminium has oxidized evenly) then it will not even be noticed.!  But to my mind - it is the details that you don't see which can make the difference between something looking right or something looking just a little odd.  

Enough of my prattling on today.  I bid you a good evening.


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Me Big man.. me make big mess in kitchen !


^ a quick check for flatness of this sump's gasket face reveals a corner not sitting flat by 0.003". 


^ 320 grit wet n' dry taped to the flattest part of this kitchen worktop ..and with a little elbow grease + soap n' water - its gasket face was trued up a little.


* I use a felt pen (waterproof ink) as a very convenient substitute for engineers blue.  It works well.


^ the sump's gasket face is now very flat aside from a dint ..right next to the middle stud hole in its forward end (to the right you can see what looks like a black dot).  As engine oil might seep passed this and out through the stud's hole - I'll fill that dint with a spot of Araldite.   The new spacer was as flat as any I've yet bought and was generally fine after a few minutes work, aside for a slight low cut (see blue across either end). It been milled but this one cut was perhaps a thou deeper.  A bit more work on the wet n' dry pad took the surrounding aluminium down so it's barely discernible now.

So I moved over to checking the rocker cover's gasket face and that of the engine's timing chain inspection cover.



^ the rocker cover I had done before and so this was more a check than anything.  And this particular cover is in excellent condition.  Sadly I've come across so many which have been abused over the years with careless handling, over tightening of the three studs (which cracks the casings and then need welding), and most are badly bowed. Some I've known to have 0.035" or more distortion.  This one shows a little hogging, but it's now less than a thou, so as I double up on the card gasket I use here - I'll leave it as is.

The gasket face of the little inspection cover though is pulled down at every fastening hole.  I could slip a 0.006" feeler gauge inbetween the worktop and gasket face, in the short span between the holes. That's more than the gasket can take up, so it must have been leaking badly when last use.


Awkward little so n' so to hold down and rub against the wet n' dry., but little by little it succumbed to the threat - be flat or be scrapped !


So, only an hour of work today ..but an hour in the right direction is better than non at all. 

......even if it take me a further half an hour to clean the kitchen again !  :wacko:


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Just two to three hours yesterday to quickly report on. .  


^ For a 1953 motorcycle engine these bores, lightly de-glazed with fine-grit wet n' dry, are in remarkably good shape - not least because they are still to the original standard size.  But as you can see from the photo they are worn.  It's more visible than a hard edge, but measurements suggest there's 0.004 - 0.005" of wear.  The vertical scoring lines are visible but are so shallow as to be immeasurable and not felt ..so perhaps just 0.0005 - 0.001".? 

The 1/4" high rim around the top is where the piston rings (which are situated part the way down the side of the pistons) don't wear.  The darker colour immediately below this is where most of the wear occurs because that's there the top two compression piston rings come up to and as the conrod sweeps over tdc they stop and cock sideways a little ..and then under the full explosive power of the combustion are pushed about and accelerate away again.  And of course, near the top of the compression stroke the cylinder is densely packed of air-fuel mixture, and the latter part of this dissolves lubrication on the cylinder walls.

In the present circumstance of our country's lock down I can't just take the block in to the machine shop and have these rebored to +0.010", so I'll just replace the piston rings and use things as they are. Let's face it., this bike will probably not average more than a couple of thousand miles a year anyway ..so it will last another 10 years without issue, by which time I'll be in my mid seventies so I won't worry too much about squeezing every last ounce of performance. 


^ here I'm using a Demel with small sanding drum to reduce that rim's step-height.  The primary reason to do this is so the piston rings, when correctly sized (tight) to the slightly worn bore, will also slip passed this lip as they are fitted with piston into the cylinder.  Even if a remnant of the lip remains and it's rough - it'll not be an issue because the pistons and rings do not run on that short length.


^ I then used a honing tool to de-glaze the cylinders.  The very fine scoring the stones produce helps retain lubricating-oil as the engine is run in, and also help the new piston rings to bed in (wear to a very snug fit). 

With this tool, I use a cordless drill at its slowest speed (controlled by trigger pressure) and at the same time I bob it up & down ..so that scoring is at an angle to the piston rings (rather than straight the way around - which would tend to snag the rings).  I use thinned engine oil (50 / 50 new engine oil to engine parts cleaner) as a cutting lubricant.  Aside from clagging, this stops the grindings of metal and stone becoming airborne dust, so although it's messy - it can at least be seen, contained and more easily cleaned up.   Naturally it has to be thoroughly cleaned from anywhere within the engine before reassembly.   


^ New old stock Hepolite piston rings versus Italian made ones.   oh the nostalgia in old packaging. I love it. 


^ interesting that it says Sunbeam 1946 / 52, when these bikes were made through to 1956.  Perhaps these piston rings were made in 1952 ?  I also love the long-hand £-s-d arithmetic scribbled on the back of the packet. 

"Ring gaps should never be less than 0.003" per inch of bore diameter, or for racing engines 0.005" per inch measured in an unworn portion of bore" is interesting because the Sunbeam manual specifies 0.004 - 0.006" for its 2-3/4" bore.  (Hepolite figures being 0.003 x 2.75 = 0.00825").  Personally I've found from experience of these engines that too tight a piston & rings tend to seize during the running-in period, so thereafter I used 0.008" for the top compression ring (which gets hottest) and 0.006" for the other three. Perhaps I ought to up my figures.  The Italian piston rings don't specify any fit, but I might only presume they would expand as much as the Hepolite rings ..despite their being much softer steel  (..evident when I was filing their length and also in their springiness). 


^ I use a short bolt as a measuring stick to accurately position / level the piston ring all the way around - a set distance down the bore.  The length of this corresponds to the level of the top oil scraper ring on the piston, and this in the bore is hardly worn.  The overlap of my 0.010" oversized rings is then marked using a fine felt pen. . .


^ and then that is filed down (using a square sided wooden block to help keep my filing true / square).  It's a time consuming task filing (deliberately cutting too little) then repositioning the ring back in its bore to recheck the measurement and also that the filing is square ..to the nearest fraction of a thousandths of an inch, with feeler gauges (below) and then filing a little more, re-measuring again, filing some more, and so on ..until the gap is spot on.   

BTW, the ' T '  I mark on these is simply to more clearly highlight which is the top face of the ring (the sides have a slightly tapered angle), and then I only ever cut / file the other end of the ring  ..only one end is ever touched so needs to be kept square.   


^ checking the end gap with feeler gauges.  

Tip ; even with freshly rebored cylinders there's always a slight difference in diameter of the bores. It may only one thou of an inch (machining tolerance) but as a perimeter measurement (which is what the ring's end-gap is measuring) then that 0.001" difference in diameter = 0.003" difference in end gap.  So it is good practice to measure and file your rings for the larger diameter bore.  And then if you file a tad too much (perhaps if that cut didn't go perfectly square and you want to true it up), then you can use that ring in the other / tighter bore.


^ these are the Italian rings, each measured and carefully filed to size.. Each is marked to indicate which cylinder, and which piston's ring position it is to fit into.  I've cut these all to be 0.005" end gap in accordance with the Sunbeam Workshop Manual (seeing as these bores were already worn near their top) but after reading the instructions on the Hepolite packaging, I think I'll go back and ease them just a little.



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On 3/28/2020 at 9:11 PM, Mally said:

I couldn't see the point in sawing a line in the spacer, but when it's together it makes a huge difference,


Completely agree with this.


Do the bores wear equally on these engines? 

I am presuming that the rear cylinder runs hotter - maybe wears more, (or seizes more often!) ?

As ever, fascinating reading and inspiring work.

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Hi Azimo,  likewise thanks.

The bore wear is pretty even cylinder to cylinder,  but contrary to the obvious - the forward one runs hotter and is more prone to seizure.  I'd suggest the reason for this lies with its design utilizing the oil  (return from the camshaft) running down and splashing around inside the cam-chain chimney ..which in turn dissipates heat from the rear cylinder's casting to the aluminium cases including that of the bell housing - that acts as a massive heat-sink.   So whereas the forward cylinder has relatively thin cases and mostly relies on air-flow past it,  the rear cylinder relies on the excellent conduction properties of chunky cast aluminium to transfer the heat away.  The heat management / balance of these engines is imo very clever.  Of course the real 'hot spot'  is the rearmost segment of the forward cylinder where the heat between the two cylinders has almost nowhere to go. ie. the most common seizure is just above and below the gudgeon pin on the rear face of the forward piston.

postscript :  Wear within each bore though is the typical vase shape as illustrated below  (..' vase shape' but of course I am taking about thousands of an inch ) . . 


^ although to scale - it is much amplified to illustrate the wear.  It was measured by recording a single piston ring's end gap at different heights down the same bore.

Its end gap ranged from 0.007,5 to 0.028",  so a difference of  0.020,5".   As this is a measurement of perimeter, that figure divided by pi  (a constant at 3.142) is the difference in diameter.   ie.,  20.5 / 3.142 equates to upto 6.524 thousands of an inch wear in the bores. 

The wear in this bore means the piston ring will have to squeeze tighter (like a piston ring compressor does to it)  by that 6.5 thou ..during every stroke.  That's not good for ease of starting - and it will amplify subsequent wear.  It really ought to have a rebore soon (bearing in mind the coronavirus is preventing that happening at this time).   A ten thou (+0.010") rebore would make the cylinder walls straight sided again.  But for an unknown reason - these pistons are not available in a +0.010" size. So the first rebore size is 0.020".  

Still, the illustration above is useful insomuch as it tells me where I  should have been measuring the piston ring's gap.  ie. 7/8" (third point down) from the top would have represented the tightest diameter, and therefore perimeter, in this cylinder's bore - And that is what we need to work to ..because piston rings expand in length (so become a tighter fit within the perimeter) as they get hot.

But I got it wrong :huh:   I had measured the end gaps at a level 5/8" down the bore (indicated by the second point down in the drawing). Because of this I had to remove all the rings and re-file them / to increase each end gap.  To be safe, I've now used Hepolite's recommended 0.008" gap ..at the tightest place, ie. 7/8" down the bore (third point down in the illustration) and checked them again at the bottom.

Fortunately,  I had not followed the workshop manual and used the minimum 0.004" end gap.  If I had - then when heated up (..by the combustion process) and thermally expanded  ..they would have locked up.!

Hey ho  ..even I am still learning..  In this case to measure where was the tightest before filing all the rings.

- - -

  This afternoon I was doing the same (piston ring gaps) on Pudge's engine.  


^ This was easier and quicker because it had already been rebored, so no rim around the top of the cylinders and no wear immediately below that ..so the bores are almost parallel sided. The rear cylinder is however one and half thou smaller in diameter.   That's a little odd, if only because some machine shops anticipate the rear cylinder running hotter and so leave a little extra room for expansion.  But this one is to the contrary. 

Anyway no lip meant that placing the piston rings in to check / measure them was a swifter task, because I only needed to aligned them just inside the top. Only when fine fettling the finished end gap size did I position them further into the bore.. Then I used the thickness of a nut as a 'measuring stick' for the compression rings (..so that positioned them about 1/4" down the bore), and then the same short bolt as used previously as the measuring stick for the oil-scraper rings  (.. so those rings were eased 5/8" down the bore).

I did have to be careful though because those Hepolite piston rings are very hard and brittle ..needing to be handled with extreme care.  The difference is that they are cast iron which were machined and then surface hardened.  Cast iron makes a very good spring which is also very hard, but you cannot bend it very far at all.  The Italian piston rings are most probably made by rolling high carbon steel, which are then machined to shape, before being surface hardened.  The springiness is less but they bend more and so are much easier to handle, without breaking.  Same job but very different characteristics.

Anyway that job is now done, with my following the end-gap guidelines set out by Hepolite (so ignoring what the Sunbeam Manual says). All these rings are set to 0.008".

- - - 

As an aside, I guess this is an opportune moment to briefly discuss removal and refitting of rings to the piston.  Many of you will know how best to do this,  so it's just a guide for those who are new to tinkering with old motors. .


^ Bottom oil scraper ring ..also known as oil control ring(s).   The oil scrapers are wide and have double blades to scrape oil around the piston (see its  shiny edges above).  I gather most people think of an oil scraper / oil control ring's job is to stop oil from the crankcase getting passed and up into the combustion chamber. But that's mostly not their purpose.  Actually the piston has numerous drilled holes within this groove ..purposefully to let oil into the gap between the two blades. And then as you can see there are more holes drilled between the two oil scraper / control rings fitted to these pistons.  And so the rings are like oil galleries ..to route / transfer lubricating engine-oil all the way around the piston skirt and the cylinder walls.  NB., unlike these solid but slotted piston oil-scraper rings (seen above) - modern ones generally have two blades and a corrugated style of spring inbetween them (to hold the blades square / in place).   But the same principle applies ..of letting a controlled amount of oil splash and oil mist from the crankcase through to lubricate the piston running up and down in the bores.  

Anyway because these solid (rather than spring) oil control rings are wide  (almost square in section) - they don't easily bend or twist.   So (above) you can see me using two old feeler-gauges to slip between the piston and the ring.  I carefully lifted one side of the ring out of its groove, and slipped in one of the feeler-gauges to suspend the ring above its groove. I then slipped in a second one ..and carefully worked that around to the other end of the ring.  Some folk slip in a third gauge, to hold middle of the ring out of the groove while the first two are eased towards (and therefore lifting) the ends of the ring to very gently lift them out of the groove.  The ring is then slid off the end of the piston.

P1340207s.thumb.jpg.09fca107a0cefd388924261289a6cef9.jpg .

^  Personally I prefer not to use a third feeler gauge, but instead I carefully twist / ease the ring over the bottom of the skirt - so it can curl inwards to a smaller diameter (..less stretching to the limit) .

P1340208s.jpg.6a5c9af4659f88bd07d937e356086994.jpg  .

^ I do the same, gently twisting over the end for the top piston rings.  I find the sideways flex is more forgiving (less breakages) than stretching the ring outwards all the way around to the much bigger diameter. 


^ however the top oil scraper / control ring cannot twist / sideways flex enough, so for this one it is a matter of inserting the feeler gauges ( 0.008 - 0.012" thick ones work best) and very gently easing this ring outwards so it might be slipped upwards and over the two compression ring's grooves. 

Fitting piston rings is a reverse procedure.  I fit this top oil-scraper before any of the others, by resting one end of the ring onto the side of the crown and gently pulling (springing outwards) and curling / twisting the ring onto the feeler gauges, before sliding it down to its groove.   And then the feeler gauges are moved around ..away from the ends (one at a time) so the ring's end eases into the groove.  It is a task that might benefit from having three hands (..together with a fair degree of patience) but of course is manageable on your own.  If in doubt.,  practice with the old (worn out) rings before trying to fit brand new ones. 

It's really as simple as breaking twigs.  

.               Argh.. did I just say that out loud !  :ph34r:


With the old piston rings carefully (..I never know when I'll need a used one - in case one of the new ones darn-well breaks !) removed,  I could clean up the pistons ready for fitting with new rings (already perfectly sized to each bore). . .


^ Just so many oil holes through those pistons !

Hopefully from a quick glance you'd never guess these were very old pistons ..that had been up n' down tens of thousands of times before.  I even polished up the gudgeon pins (..still a good tight fit).   Tomorrow I'll do the same with the other engine's pistons.


That's it for tonight folks.  Take care and a very good night to you all.


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evening all.,   This afternoon's task was to weight match the pistons and rods  ..after cleaning up the second engine's pistons and rods.! :blink:


^ Standard size and in really good condition.


^ after general cleaning I set to with cleaning out the crud from the grooves, using a needle file. Almost no pressure is required ..after all I'm just removing the oil deposits and don't want to cut into the aluminium itself.  Another time consuming task ..but tbh I couldn't bothered to get the de-carb acid out.  


^ again carefully cleaning out the burnt-on oil crud out of the oil drillings (..my last post which explains why).  I'm using a 2.5mm drill bit here, and many were blocked to less than 2mm.


^  Those in the skirt,  rather than in the grooves, are at an angle.   There's also a couple more to be cleaned out inside the piston (of 3mm size) which are to lubricate the gudgeon pin. 


^   #1 cylinder's piston has light scoring and pitting (from heat) from where it had seized at sometime (..perhaps when new).  It's usual and this is as good as the best I've seen ..and certainly redeemable.


^  yes I'm a butcher !! .. I used a power file to linish it down a little


^ ..and then 400 grit wet n' dry to smooth it again.  That'll be just fine.


^ it's difficult to see from the photo but the (+0.030") piston on the left, which is from Pudge, has a much rougher internal casting with cast-in part numbers ..and their skirt thickness is perhaps twice as thick as the standard size piston from Nudge.   Of course with it being oversize I cannot even guess its age.  

I checked the weights of these and found them to be pretty darn close.  The naked pistons were 243.3 and 242.2 grams respectively and their rods with big end bolts & shells were each 342.4 grams.  I'd say that's pretty good for a 1950's vintage road bike.  However the gudgeon pins were odd. One was 74.7g and the other 64.6g.   

The standard sized pistons from Nudge's engine were 20g lighter but not quite so well matched at 214.1 and 220.0 grams respectively. Its rods (again with bolts and shells) are 349.6 and 351.9 grams respectively.  Perhaps tomorrow I'll see if I can lessen these differences a bit. Again the gudgeon pins were odd, as if they had been mixed up between the two bikes ..which I can assure you they were not. But they were similarly out at 66.7 and 75.7g respectively..  Coincidental but a very similar difference in mass to those from Pudge's engine.

I have a spare set of pistons and rods in my shed, so pulled the gudgeon pins from those  . .


^ gudgeon pins (in order) from three engines.  Despite it being heavy-weight, the first from Pudge's engine is 1/16" shorter than any of the others. The third pair (right) are a matched pair at 61.0 and 61.3g respectively.   I'll use those for one engine and the other two lighter ones for the other.  They are all a good fit anyway despite there being no little end bearings on these bikes. I guess they are so lightly loaded with either 6:1 or  7:2 compression ratios. 

So that's it for today ..


Have a good evening.


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