Tag Archives: Eddie Shermer

1932 Flying Squirrel Racer, Engineering, New posts, Scotts

January 2015 – Progress report

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Well, we are moving in the right direction (I think) but I’ve a lot of ambitions this year so we’ll see how it works out…

Last weekend I decided to drive up to Leicestershire to see Roger and to help him improve security at his place, following the break in the previous weekend that resulted in the theft of a Yamaha RD 350 LC YPVS F2 (the one I had when I was 18 years old.. 25 years ago). He’d bought lights and I bought an alarm system and over the weekend we fitted it all and made the best of a bad lot.
I love being in the workshop and he’s still pushing forward with improvements to machinery and tooling, the latest being a DRO on the beautifully made Smart and Brown 1024 VSL lathe. You don’t need them, but they do make life easier and quicker.
It’s also good to be surrounded by his Scott engine work and I think we help motivate each other to do the best we can to make sure that our racing Scotts are in good competitive order for riding this year.
Sometime on Sunday morning we had a visit from Eddie Shermer, the editor of ‘Yowl’ (journal of the Scott Owners Club) and a skilled engineer in his own right. He and his wife also put great energy into organising the annual ‘gathering’ of the Scott Owners Club held at Abbotsholme School in Staffordshire.

Eddie Shermer, Roger and Thiel 158 universal jig mill. They were smiling until the photo!
Eddie Shermer, Roger and Thiel 158 universal jig mill. They were smiling until the photo!
Eddie does a lot of Scott transmission work but also takes on complete engine rebuilds too, and came to discuss possible solutions to a particular problem he’d encountered with a crankcase. It was good to see him and always interesting to discuss the engine issues.
In fact, I kept a Scott line going through the weekend because I’d arranged with Alan Noakes in Lincolnshire that I’d take the Silk Scott frame up to him so that he could make a start on the frame connectors. Lincolnshire is hardly on the way back to Devon, in fact around 2 1/2 hours in the opposite direction, but it meant that I could see Alan and chat through some of the details and also see some of the things that he is working on. He had some hardened and ground clutch hub centres as well as pressure plates that he’d made on the bench, and also a very compact roller starter that he’d even cast the rollers for. Very impressive.
Anyway, I couldn’t stay long as I had a 6 1/2 hour drive back home! Just back by midnight.

This last week, I’ve removed the carburettors from the Super Squirrel as I need to make some modifications for the return to petrol. I never had the twin carb set-up developed for methanol anyway (switching back to petrol this year) so it’s not something that I wouldn’t have to do anyway. The two carbs are Amal 276, but are of different bore sizes at the moment. I need to get them bored out to 1 1/16″ and also have some short inlet ‘trumpets’ made. They won’t be very trumpet like, but will just have a better radius for the air flow.
I’ve also got some ‘K-type’ thermocouples which I want to fit to the exhaust, fairly close to the exhaust manifold, to give extra information when I take it to so a dyno setup when the inital carburettor modifications have been done. Petrol will make everything run hotter, and I’ll need to be careful to try to make sure that I do what I can to make sure that I’m not overheating the piston. I may also fit a temperature sensor to a spark plug to read that, as well as coolant temperature to see whether the small radiator is able to shed heat. It’s possible that I could pressurise the radiator to help the situation, but it might not be necessary. I also have a slightly rough, larger radiator that I bought many years ago from the late John Hartshorne, a prominent Scott enthusiast who had some wonderful stories, not least from his work with Wilf Green in bringing East German MZ’s into the UK in the years before the ‘Iron curtain’ came down.
Also on the agenda is crank counter-balancing. A Scott engine, being a 180° twin has reasonable primary balance, and normally they are known as being fairly smooth engines. They have almost no actual balancing on each crank assembly however, as the cranks are too small. The engine relies mainly on the large central flywheel to help dampen out the residual vibrations, which it does reasonably well. Some people have drilled the side on the flywheel on opposite sides to try to counteract the implied rocking couple effect but roger has never been convinced of the efficacy of this process. His own idea was to view each crank assembly in isolation and to work to try to balance at least as much of the big end weight as possible. In his ‘four bearing cranks’ he has two crank ‘discs’ each side, rather than the usual one. His enables him, using tungsten heavy metal (and Titanium rods) to balance the big end if nothing else. Rogers engine is very smooth, much more so than my own, and seems to want to rev more easily. We have ‘slugged’ single sided ‘Moss’ cranks in the past for a couple of people, and one of them cannot praise its smoothness enough. My cranks are not weighted, but I have some heavy metal slugs and I want to fit them. Normally, the holes are put into the cranks prior to heat treatment, as the final specification of the material conforms to around 50 to 53 HRC which is pretty tough stuff to machine. I’ve been looking into using surface coated solid carbide cutters rated up to 60 HRC to machine out for the slugs. I’ll post further information on the calculated % balance. I think it should be interesting!

Anyway, enough for now. things are happening! Even the Triumph head is back although a little more work needed here too.
I’ll try to not leave it so long as we go through the winter.

1932 Flying Squirrel Racer, New posts

June 2014 – a review

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The rebuild of the Super squirrel racer is in its final phases.. and so it has to be as it’s entered for the Beezumph at Cadwell park on the 11th /12th July. I need to do a piece on the final assembly and some of the things I’ve experimented with.
I’ll default to the single carburettor that I know works if time really dissapears but I’d really like to try and get the twin carb set up finished and ready as it really might fly with a bit of extra gas coming in.

Ovally bored single carb used on the Super Squirrel since 1970.
Ovally bored single carb used on the Super Squirrel since 1970.
One of the main reasons that Roger evolved from this single down-tube frame to the duplex frame on his bike is the ability to fit a bigger carb. He obviously felt it was holding the engine back. I thought I’d have a look at this further.

I’ve had a twin carb manifold for a few years which was made by Eddie Shermer. It splits either side of the single tube and gives you the advantage of standard two stud carb mounting rather than the unique Scott three bolt pattern. I have been intending to use the two Amal 289 carbs that I have previously used, albeit briefly, with this set-up. Although it seemed to go well at the time there was insufficient opportunity to really test its performance. That was with petrol, not methanol so a direct comparison is not possible. I have had a feeling that the 289’s will be too big though.

Twin carb manifold in position
Twin carb manifold in position

A couple of years ago, when I first set the bike up on methanol I approached various people for advice. Roger Cramp of Velocette racing fame had built and developed two strokes to run on methanol and he kindly gave me the benefit of his experience about carburation. One of the things he said was that with methanol he’d found it very important to make sure that you had sufficient gas-speed over the emulsion tube to ensure that you had adequate atomisation, and he found that he’d reduced carb throat size to achieve better results. I imagine this principle applies to any fuel, but methanol is more reluctant than petrol to diffuse it seems. My single carburettor that sits behind the downtube is quite small and it works perfectly with good clean pick up throughout the range and it’s difficult to imagine that the pick up could be better. I don’t want to lose tractability so I thought I’d look at the relative areas.
Twin carb manifold made by Eddie Shermer
Twin carb manifold made by Eddie Shermer

The inlet port on a single cylinder measures about 61mm x 16.8mm which gives around 10.5cm². I make no apology for change in units as I use what helps me visualise better! I’ve ignored the single bridge in this port, but reason that it will effectively make the port a little smaller.

The single carb I use at the moment is an Amal 289 bored out to about 32mm. This area is 8.04cm²
The 289’s I have are about 28mm bore and this is about 6.15cm². Two of these is 12.3cm²
A 1″ 276 is about 5.06cm². Two of these is 10.12cm². This would seem to be a better match.

It seems to me that I should try to at least have the carburettor inlet area quite closely matched to the actual inlet port area and that all my work on getting more gas in is a little pointless if I don’t increase the carburettor size. I think it will be very interesting to see what two of the 276’s will be like though although it’s going to be a push to get them and do the calculations for needle and jetting modifications before the Beezumph.

The engine is now together and primary chain and ‘magneto’ belt fitted and tensioned.
Securing the engine is a procedure on my Scott as it is fitted with ‘tie-bars’ which replace the lower frame rails. We tension these before the engine bolts are finally done up to pull everything together.
Also requiring a procedure is fitting the primary chain.

The Scott uses an ‘outrigger’ final drive sprocket which is secured through slots in it’s casting to the undertray. The undertray is an aluminum casting which bolts into a Scott frame and carries the gearbox and final drive as an assembly. The gearbox itself is secured using two long studs projecting from the bottom of the gearbox and passing through slots in the undertray to allow adjustment of the primary chain. Under acceleration the outrigger tends to get dragged rearwards along it’s slots, thus wearing the ‘high gear bush) in the gearbox putting bending moments on the output shaft and also encouraging the entire gearbox rearwards also. When this happens the primary chain tightens which puts pressure on the main bearings as well as buggering the chain, wearing the drive sprocket and wasting power.
One of the ways to avoid this is to cut out a little piece of metal to very closely sit in the slot of the outrigger to prevent it being dragged rearwards. Roger did this for years. Now we have snail cams fitted to the rear undertray mounting on the drive side to wedge against the back of the outrigger.
The other part of the gearbox bolting procedure is to make sure that after everything is locked in position, we make sure that the backlash in the adjuster for the gearbox position is taken out so that it also is playing a part in making sure that the gearbox is not pulled backwards. I then wire lock this adjuster nut in position. If this is not done, the gearbox will be pulled. The Scott 3 speed gearbox is a rugged device, but simply ‘doing the bolts up’ is not enough. These two procedures make sure that the gearbox stays where it should.