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Garage Diary : Sunbeam Motorcycle resto's..

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Pottering around in the garage the other afternoon saw me fitting the head-steady / top snubbers ..


^ the component parts of the Sunbeam engine's head-steady. This is a rather neat design detail from the 1940's that I think would be hard to better value engineer even 70+ years later.  There's nothing here to support the engine (..the two engine-mounts do that),  but the rubber snubber blocks do stop the top of the engine from moving sideways (ie. they counter the torque reaction of an in-line engine &/or the sideways swing of using the kickstart).  The clever part though is that the (above left-hand) plate and spring assembly is a friction damper.  

Rubber engine mounts have, for any configuration and weight, a certain vibration frequency ..whereby the harmonics of reciprocating mass and the elasticity of the rubber are in sympathy,  when the engine will tend to dance around and bounce on the rubber. The chassis and engine designers work together to ensure the harmonic do not coincide within the vehicle or machine's normal operating range.  The engine mount's shape, their thickness and hardness, their location and angle of installation, as well as the design of engine mounting plates are a best compromise ..for any one set of criteria.   An example of this was my '66 Jaguar S-type saloon which originally had been sold with an automatic gearbox.  Later in life this was swapped-out for a manual box with overdrive from an early XJ6.  But the rear engine / gearbox mount (a steel coil spring) hadn't been changed.  Most likely because of the difference in gearbox weight or c. of g. distribution, and/or operating speeds - things were not as smooth as they ought to have been ( also the exhaust pipe joints were being stressed).  Discovering and changing that spring made a world of difference to the feel of the car.  

Some designers and/or the mechanic don't get it quite right though, and resultant extenuated vibration can be clearly felt at certain revs. Often that means the vehicle is driven a little faster or slower, or in another gear to find a 'sweet spot'.   My last Norton Commando 850cc long-stroke parallel twin literally had vision-blurring harmonic vibration around 20-25mph ..which made town driving almost unbearable.   As an aside - this is when I bought the Sunbeam S8 for my daily commute through town to work.  The Norton was superbly smooth at other speeds but because of this 'issue' the bike fell into disuse.  Eventually, I discovered that by changing its head steady (coincidentally also springs) ..it moved those harmonics to around about 45mph, which was easily ridden through, not least because at higher rev's the vibration was not nearly as bad.

So, to alter the characteristic 'bounce' of rubber and therefore the combined harmonics, the Sunbeam has this damper. The assembly consists of a mounting bracket with vertical tongue (above, top of photo, painted black) which clamps around the frame's top tube. And there's the plate (chromed but originally painted black) which bolts onto the back of the cylinder head and onto which are mounted two rubber snubbers. This is all that needed to stop the engine from rocking sideways. 

But then to the left of the photo is another plate used for a friction damper (also originally painted black). This bolts to the frame clamp bracket and otherwise hangs down to overlap the engine plate.  Inbetween these is an oval shaped friction pad (made of the same material as a clutch friction plate). The two plates are held together by the pressure of a spring.  As the engine vibrates on its two rubber engine mounts the snubbers control the big sideways movement and the friction damper works to absorb vibration. 


^  For clarity (above) this is how it goes together (sans the spring & its cap ) with the friction pad sandwiched inbetween the two plates.  The large diameter hole and adjacent two larger studs is (sometime later on) where the distributor will be fitted - taking its drive from the camshaft / cam-chain sprocket.  The long slot across the bottom has a cover that is fitted over the six studs.  In the meantime - the photo helps illustrate the simple way to correctly align this assembly.

  1.  With the (two) main engine mounts and front/lower snubbers (previously) set correctly.
  2. The engine's head-steady plate is temporarily but securely fastened to the cylinder head with a few nuts (thick washers under those).  The clamp around the frame is loose enough to freely move forward n' back along the frame tube and/or twist around - so its forward-downward projecting tongue sits evenly inbetween the rubber snubbers.  [ NB. that tongue is loose on many bikes, and is intended to be held tight between the bolted-up clamp. Like many before, I weld mine to one half of the clamp - as it makes assembly much easier.  I also use a longer bolt and a spacer-tube for the lower fastening of the clamp, so it now extends wider than the plate to get a (1/4" Whitworth) socket onto its nut. ]
  3. The top plate is adjustable (up n' down relative to the frame clamp) and is set whereby the friction damper's spring bolt is positioned central within its oval hole (see above).  That is important - as it allows the engine to bounce around on its mounts without this fastening hitting the inside edges of that plate.  The tubular sleeve around the bolt fits into the hole through friction damper pad to hold it steady.  In use it doesn't move relative to the engine plate, which is bolted to the engine .. it only moves relative to the top-plate. 


^ The clamp around the frame is presently still loose, because it needs to freely slide forward along the frame tube until the top-plate and the engine-plate sit parallel / flat to each other ..with just the friction-pad sandwiched inbetween them. 

         4. The conical spring is now loosely fitted within the cap and sitting on a thrust washer. The spring can be compressed by hand just enough to fit the lock-washer and its nut


         5.  The spring's fastening is tightened - which squeezes the two plates flat to each other, with the friction-pad sandwiched inbetween.  The position of the top-plate needs to be checked and adjusted to be central across-wise and up n' down (above, blue marks) relative to the spring. 

         6.  the frame's clamp is then moved to sit flat against the top-plate, and the top-plate to frame-clamp bolts can be loosely pinched-up ..with the top-plates reinforcing tabs positioned vertically.

         7.   ...at the same time, the frame-clamp can be rotated - so its forward-and-downward projecting tongue sits evenly inbetween the rubber snubbers.  The frame clamp's bolts can then be tightened.  Only then is the top-plate to frame-clamp bolts tightened.  That's the damper set up. 

This ought to be good without subsequent adjustment, but because the main engine mounts may 'settle' with use - it is worth checking they don't need re-tuning after a hundred or two miles. 


        8.  The head-steady / top snubbers can be removed with the damper and clamps all tight. Shouldered nuts, which sit into key-hole slots in the engine-plate's top bracket, hold them in place. They are (sometimes) fitted with shims to lessen the clearance between the rubber and the frame-clamp tongue.  Personally I feel shimming flexible rubber blocks to thousands of an inch a bit of a piss-take. I use a skinny penny washer if it fits in there, otherwise if there no room for that then nothing.  imo that is close enough tolerance  ..and I really don't care if there's 0.025" gap or if the two rubbers are squidged just a little ..not least because I've never bought a pair of new snubbers, and I'm sure after 70 years the shore-hardness of the rubber I use is 'a little off ' from the original design spec.  On this engine I fitted one penny washer inbetween the plate and the left-hand-side snubber.   


^  These brackets and also the nuts and bolts were originally painted black, so the chrome bits you're seeing here are all from the special treatment this bike had in preparation for the Queen's Coronation celebrations in 1953.  I don't know what exactly was chromed at that time but I do have photos of the bike taken in the 1980's and there was a whole lot of chrome plating evident from then.  As it is mostly hidden under the petrol tank and the distributor, and behind the cast aluminium rocker cover and rear access cover I not sure I'm going to worry about it too much.  I'll very likely spot a little silver paint over the grubby bits one can see while counting rivets but that's more to prevent any further corrosion.

Anyway job done, engine mounts are now correctly adjusted.  

Sounds easy enough, so why are they so often wrong. ?


^ these plates show uneven wear from where the friction damper has been missing (..for a long while). The arrow points to the corner of the engine plate bracket which should protrude a coupe of mm.  The friction pad is positioned by the sleeve around the central spring bolt, but the protrusions prevent it from rotating.  The top plate which I'm seen holding shows wear grooves from it was face down on those protrusions. Do people not see or hear this sort of thing ?  Or is it that "all Sunbeams are shyte" because they make all sorts of squeaking and rattling noises and vibrate horribly ..when they are put together by total morons?  :lol:   I sorta guess that applies to any car or motorcycle.   

I bid you a good weekend ,


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. Ok here's a quick update of latest progress.. 


Starting off with getting the electrical box in place, which sits just below the saddle on the right-hand-side of the bike.   Within it, aside from it being the main junction box for electrical connections, are the coil and voltage regulator - so there's a decent amount of weight in there.  On its hinged door are an ammeter and the combined ignition / lighting switch.  Inside the door are spare bulb holders .. a nice detail. 

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^ The pressed metal construction is pretty tough, but a support plate (shown) fits on the underside to prevent the holes from splitting. Of course over the course of many years quite a few bikes have it missing ..and yet I've rarely seen a split box. Never-the-less, as I have them - I'll refit them.   The battery box (2nd photo) is slightly larger in size and of similar shape, but a mirror image, as it sits back-to-back with the electrical box. Inside that is a hefty cradle (Right in 2nd photo) to take the weight of the original type 6v battery.   

My intent is to move the battery (I now use a modern gel-battery which requires no maintenance) to the smaller and less-convenient-to-access tool box, which sits on the bottom frame tube next to the left hand footrest, so immediately below the old battery box.   And I'll leave the battery cradle in the garage, as I'll be using that box for tools and as a general purpose hold-all.  I decided to modify a spare electrical box backing plate (I'm holding in the 2nd photo) to fit this box, but isn't making slotted holes a pain ..in the ol' flat plate !  :blink:

Where these boxes are suspended under the frame, directly under the saddle, there's another little plate ..also with slotted holes.. 


^ I had one of these, but not another for the second bike ..so while it was off - I used it as a template to make a second. 

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^ although I temporarily positioned both boxes (to ensure they were aligned to each other and the frame) - I then took the battery box off for easier access to the distributor and when re-tightening the cylinder head bolts while running in.   NB. the small plate, I made a copy of, sits on the top of the electrical box (indicated by red arrow) and its main purpose is to lower the box by that 2mm plate's thickness - so the hinged doors of those boxes doesn't scratch the frame.  It's an odd detail which might easily have been overcome by combining the frame's two brackets and lowering it by the 2mm.  Hey ho., I'm probably missing something profound.


Moving on., with reassigning the use of the tool box ..as it used to be, to now be the battery box. .


^ two modern 6v - 4.5ah gel batteries (taped together) I've been using.  These are petite compared to 1940 - 50's  6v lead-acid batteries ..and they'll tuck nicely out of the way, inside the (former) tool box.  To level the box's floor (which has the heads of its mounting bolts protruding)  I cut a piece of 3/8" thick plywood to fit in there. Subsequently painted, I then glued a couple of strips of rubber to its underside, so as to offer some insulation from vibration.  I also drilled a 3/8" (10mm) hole in the rear curved face of the steel box, through which I'll run the battery leads to the electrical box. There's wiring to the brake-light switch and horn down there anyway, so the battery wires will run together with those. 

Although no fuse was fitted originally, I use a spade-type fuse (within a watertight holder) on each of my bikes., so I'll place that conveniently - for when I want to connect the top-up battery charger.  And yes, I did touch-in the paint around the hole I drilled.    

I acknowledge moving the batteries to down there is bit of a compromise ..not least because the former battery box now has to be removed to get these batteries out and off the bike, but that's not a big deal me as it's not something I do very often.  And I'll just make the old battery box q.d.  That occasional inconvenience is little compared with now having a usefully sized (double the volume of the tool box) and easily accessible handy cubby hole box to stuff 'thing's in. 

- - -

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^ for ease and to save my back while I fit the engine's ancillaries & exhaust, and to do a few jobs on the wiring - the bike is now back on the lift (home modified) . Under the white-painted crate is a Sealey bike lift,  which I found to be useless when changing the engine oil and otherwise very dangerously unstable.  But with the (3/4" thick plywood) crate bolted onto it, and the extension to support and securely clamp the front wheel,  plus the addition of legs under that end - it is now a useful bit of kit.   ;)

So, onto the exhaust pipes . .


^ aluminium headers and (as fitted to Nudge) stainless steel down-pipes .. looking Ok., but a little dreary from that bike previously being used for my all-weather commute to work.


^ With a good bit of elbow grease - the down-pipes in particular came up better than I thought they might. B)

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^ Yes that's pretty  


^ It's an after-market down-pipe, supplied by Stewart Engineering, which for some inexplicable reason are always too long (see arrow). I've had this several times when I used to restore customer's bikes. Then I'd have to chop 3/4" off the top of the tubes. Those fitted to Nudge (as bought and subsequently used) had a stepped kink in its flexi-pipe ..but it's a job which I really ought to do correctly now.


^ Conversely., these are the chrome plated steel down-pipes off  Pudge  ..which as you can see are the right length (height).  As this is Pudge's engine, I may as well use these for now, and sort out Nudge's later on when I fit her own engine.  

So back to polishing..  these pipes and its aluminium headers.


^ I'd already had these apart so there was less work to do.  The gasket face of each header (..to the cylinder head) did need redressing back to being flat though.  The above shows the olive used to (mostly) seal between headers and down-pipes, and how the screw collar joins and clamps them together.   It works very well as a very firm assembly, but the exhaust gasses blow through the split in the olive. 

I'll fit them for now, knowing that this will blow ..and I'll come back after a few heat cycles (starting the engine and letting it cool again several times - to let things settle in place). Then I'll apply a little exhaust sealing putty.  Again during assembly I use copious amounts of Coppaslip, which smokes like anything for the first 5 minutes ..but it does help prevent corrosion and binding of the aluminium threads, as well as helping the pipes slip together and be unstressed. 


^ Next up was to clean the exhaust silencer. On the S8 (Sunbeam's more sporting model with slim section tyres), which Nudge is, the exhaust silencer is cast aluminium and of a narrow upswept design.  I guess it is Art-Deco in style ..which I think is rather nice.  I don't honestly know what the original finish was - but I'd guess it was most likely to be cast matt or grit-blasted finish with just the styling flashes being polished bright.   Of course, over the course of 70 years, these exhaust pipes get salty and scarred ..and have otherwise been polished and then scarred again.  If I was getting anything else blasted I'd take it back to matt, but as I'm not - I'll quickly rub it down and polish it up yet again. :P 

Can't really complain when one thinks that this (very likely to be a 1953 exhaust silencer) is still going strong and in use today !


^ Polished, fitted and if I might so  - looking rather neat.  B)

So, another job done. 

The clamp for the back end of the flexi-pipe (which of course is used because the engine is rubber mounted) extends inwards and is bolted to the underside of the frame, so the silencer's front end is held secure.  The silencer's weight is mostly carried on a hefty stud through the base of the rear suspension upright.  There is also another bracket, from the down-pipes to the underside of the gearbox, but for whatever reason that bracket has been cut off.  That's of no concern, as I've done without it before - and not had an issue.

Just one last piccie for today, and that's taking a step back to earlier in the afternoon when I loosely positioned Pudge's  exhaust silencer on this same bike and down-tubes.. just for comparison. . 


^ this is the Sunbeam S7 and S7-deluxe exhaust silencer.  I understand that with the narrow wheels and tyres on this bike (an S8) the rounder and lower set silencer tends to grind against the road on hard corners.  The fat tyres of the S7 are enough to make the difference. 

To our eyes, its chromed metal may look quite commonplace  ..and with its mounting clamp (by the rear suspension) being on top - not so attractive as the (less expensive when new) S8's silencer.  I guess in the 1940's ; cooking pots n' pans were made in aluminium whereas chrome plated fittings were something special.

I'll leave that thought with you. Have a good evening,



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On 5/22/2020 at 6:29 PM, Bfg said:

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)

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ebay link < here >

Batteries arrived today and I was surprised that they were a.) Yuasa batteries,  b.) they are 12ah,  and c.)  it says on the front "Designed For Standby Use" . . .


^ The e-bay advert is misleading but I'll give it a try anyway.  I'm not worried about it being 12ah rather than 14 because they are replacing 2x 4.5ah = 9ah batteries.  "Designed for Standby Use"  is of concern because that implies very trickle charging ..so  I tried to call the seller on the number given on the delivery slip and on their ebay listing but that didn't go through (as if it's a disconnected line).  Hey ho.

Good news is that the size of the batteries works very well in its new location . . .



^ with this battery sitting on a pad of 1/4" neoprene, on top of the 3/8" plywood, which is sitting on foam rubber strips to isolate the battery from vibration - the height in the box is perfect. The lid of the box is a domed so there will be enough space for a 1/4" thick pad on top as well so the wires will not touch.  The narrowness of this battery (2") also means that this battery can be fitted or lifted out of its new home without disturbing the (former battery-) box above it. - That's an unexpected bonus :)

There's another 1/4" thick pad of neoprene inbetween it and the outside of the box and 1" polystyrene packing around the other three sides. so it's snugly in there and cannot rattle around. 

As long as it works re. charging I reckon it should be a neat improvement, insomuch as in freeing-up the sizeable former battery box for things like my waterproof over-trousers and in offering easier access for tools stored in there. 



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