The Super Squirrel racer … where we are.

It’s not been the best couple of weeks for getting on with the Super Squirrel racer’s engine with both my wife and little girl both poorly and work being very busy indeed. A very good friend of mine also passed away, although this did rather contribute toward the quietness and patience required for gas flowing with riffler files.

So what is the plan?

A bit of history… In 2006 I finished re-building the old Super Squirrel racer and into it went a good Scott engine that I’d built with Moss crank. I sold this engine to fund another more radical engine build, and machined up my own head and heavily modified a Scott barrel to suit. I also welded up my own expansion chamber.
The crankcase I used had been a damaged case that we’d had welded, but had some evidence of cracks still remaining beyond the welding.

Anyway, I took it to it’s first BHR meeting at Mallory and it felt really strong for the first two laps, before it died. I didn’t really look at the engine until I’d pushed it back to the van, but when I did I realised that the damage was absolute to the crankcase. It was split in two and completely irreparable.

oh dear.
oh dear.

Upon reflection, the case wasn’t up to the job. I might have had some tiny amount of piston/ head contact too.. I know they were close as I’d had it before during testing and had worked to increase the clearance. The main bearing assembly was experimental and I think that also may have been a weakness. You live and learn and competition sometimes just brings the answers a bit quicker.

I had been working with my dad building the engines for a few years and I think this just happened just as I was going to move on to do a contract working to changeover a cylinder head line to a new head in the casting plant at Nissan in Sunderland. As I was not in a position to build another engine, my dad resolved to machine up one of his crankcase castings to at least provide a sturdy basis for a race engine. Into this he built the internals of the previous engine, and the new engine was badged ‘Phoenix’ in reference to it’s resurrection from the remains of its predecessor.

from the ashes...
from the ashes…

It was a fantastic thing to do for me.. I think because he felt quite sorry as I’d put so much work into the previous engine and also, that he felt that the far stronger crankcase casting was a far better place to start.

So I ran the engine for a couple of years, on petrol, and it kept going, but it wasn’t really competitive. It wasn’t really ‘tuned’, just solid and although I really enjoyed my bike, it wasn’t anything like as good fun to ride as my dad’s Flying Squirrel, which just had a sense of thrilling urgency that mine lacked utterly.

The catalyst for the major improvements that came was when my wife and I received a wonderful wedding present in 2011, in the shape of a new expansion pipe that my dad had made to fit by Gibsons exhausts in the South East.IMG_6831IMG_6828 My wife found this quite amusing. It was somewhat better looking than the one I’d welded up myself.. but did it work?

The first test came early in 2012 when we participated in the Prescott hill climb in aid of the blood bikes. With the same jetting as previously used with my old pipe I accelerated from the line hard and then pulled in the clutch quickly as it seized on the needle as I rolled it off.

We played around with it in the afternoon, changing plugs, altering the timing and jets but it just seemed to be running very hot. The next outing was at Lydden with the BHR club and we put in an extra head gasket to decrease the compression. It was still running a bit hot, but better… at least it finished a race. It really wasn’t quick enough though. I realised that I needed to make a decision.

It may be that the exhaust is not of the optimal shape and there may be a build up of heat because of this and not simply because it’s charging the cylinder so effectively… but we are not running a blank cheque development program (!) and so we needed to try and see if we could get it to work.

I figured I had three obvious choices. The first was to put my pipe back on. I did not want to do that .. It seemed such a retrograde step. The second was to work on getting the heat away. I’ve got a speedway radiator in the bike so a bigger one may well be much more effective. Also my dads bike has an aluminium cylinder barrel which also transfers the heat away from the exhasut port and cylinder head much more quickly than my iron block. Great. A new radiator would be about £1000 and a cylinder several hundred.

The third way was not popular with my dad.’Dope’ I said, that’s what I’m going to do, ‘run it on dope’.
The positives of methanol are that it really cools an engine and allows a far higher compression ration to be run than with regular petrol. Methanol also burns more slowly and that can make for a smoother and more progressive power delivery. On the negative side, it’s comparatively harder to get hold of, more dangerous to deal with and you need a much larger amount to run on. I’ve also experienced lubrication issues since I’ve used it, but it may be that some careful development may improve that. It also doesn’t give much warning in terms of plug colour if you are running lean. It tends to let you know by melting a hole in a piston apparently.

So it was that I invested in a barrel of your finest methanol and talked to a few people who had experience using it. By far the most useful contact was Roger Cramp, who used to race the highly developed Velocette that his son Ian now campaigns with the BHR. He had been involved in the building and development of an ariel leader that he had run on methanol as well as a Greeves. He confirmed the research I’d done about the necessary changes to ignition timing but also said to be aware that methanol was singularly averse to atomisation (at least when bucketing it in) and that high intake gas speed really helped. This encouraged me to stick with my smallish single carb to at least try out and see if it worked.

I decided on a huge 980 main jet and then measured the needle jet with a taper pin. I then put the carb together and drew lines on the needle at 1/4, 3/4 openings at the top of the needle jet and then worked out the dimensions of the needle at those points against the aperture open for air inlet. I ended up with a pretty severe taper on the needle, but it seemed to make sense.

I advanced the ignition by about 7°, closed the plugs right up and pushed. It fired up and it ran, albeit a little roughly, before I put it in the Van to took it to the last BHR meeting of 2012.

It was brilliant. The jetting seemed to work fine and there were no holes in the power delivery according to throttle position. The bike pulled and was so much fun. It felt totally different to my dads bike, but the torque and flexibility of mine suddenly made it feel like a completely different bike. It absolutely hammered the clutch though (as it does tend to with three gears) and I was up to 1am on the Saturday night stripping, releasing, filing plates and and rebuilding it.

2013 came and one of the first jobs I did was to rebuild the clutch with new GFS plates, laser cut. They were perfect really because I had to dremel each one to fit with abut 0.010″ clearance. The less clearance, the less hammering… My dad also had some pressure plate he’d had made out of solid, which didn’t flex like the original ones. IMG_3703These didn’t have the adjustable clutch actuation pins I normally used, which are a pain to set up. I made pins up instead from some silver steel and got them within 0.001″ of each other using a cordless drill as a chuck, a file, a dremel and some emery cloth.

We took it to a couple of track days, and then the last Cadwell park in 2013 and (with new 21″ racing tyres robbed off my dad’s poorly Flying Squirrel) managed a couple of second places and even a fastest lap. It was flying, although not in the league of Mike Farrel on his Rudge, who was really out on his own and un-catchable for us at least. You can lose a lot on the start as it’s difficult to get off the line with three gears when you’ve geared top for a long straight. Except for a CS1 Norton belonging to the famous Lewis family who’ve been campaigning Triumphs and the Norton for many years. I think everyone else runs four gears. It does make a difference.

I ended the weekend having blown three composite head gaskets and with the feeling that there was a bit too much piston slap noise, but apart from that it was the best racing weekend I’ve ever had at Cadwell. I also knew I needed to strip the engine and that I’d do some gas flowing whilst it was apart.

And that’s where we are!

Smart and Brown stripdown continues…

I’ve stripped the saddle off and have had the chance to see the good and the not so good.
The mechanism which shifts the main power travel feed to either the cross slide or the main saddle seems to be in really good condition and is a joy to behold.

Feed direction indicator on front of apron
Feed direction indicator on front of apron
In fact I think most things seem to be fine although I plan to diss-assemble, clean and lubricate everything even if there’s no actual damage.
Both the top slide operating screws and nuts are very worn though as well as a few other bits and pieces.
Fortunately, I’ve made contact with somebody who has most of the bits I need, which is great.
The saddle is worn though and I imagine the top slides too, so there needs to be some precise measurements of wear and then some decisions made about refinishing work.
This is a fairly big deal, but it can be sorted out.

I think when I’ve got the bits to repair it sorted out, then I’ll put a cover over her and leave her until the end of the season and just do some research on bed repair in the meantime. I don’t want to hurry this as it’s likely that I’ll have this lathe for a very long time. That’s my plan at least. Now I need to get back to the bikes. Really my priority has to be my Super squirrel engine, otherwise I’ll have nothing to ride this year. The Silk Scott racer’s frame is high on the agenda too.
Last week I picked up some 5mm MS plate to make some engine plates out of for the Norton model 18 and I have a plan for the Triumph engine…

Lathe inspection begins

Well, It has not been sitting in the corner of someones de-humidified workshop for 60 years with a dustcover on.

The cross slide and compound slide both had a bucketful of backlash, so I took them off last night to check out the leadscrews and nuts. I’ve stripped the cross slide completely and the leadscrew was pretty badly worn, with some damage which actually chased out the brass nut.

Cross slide lead screw
Cross slide lead screw
Amazingly I just found one on ebay(!) and snapped it up. I haven’t stripped the compound slide yet but I’ll probably do it tonight.
The next thing to do is to take the saddle off and look at the underneath.
Cross slides stripped
Cross slides stripped
Part of me really wants to strip the thing completely and have the bed re-ground, and scrape the saddle.. but that’s a reasonable amount of work.

Also I’ve found that the brass helical back gear drive from the main spindle is badly worn, but it might be ok. Wonder what the spares situation would be for that?IMAG0611

The more I look at this lathe, the more I like it. The details are superb.

Model M: forward/reverse
Model M: forward/reverse




The eagle has landed!

A few extra bits of bracing on Sunday morning and a trip to Screwfix to buy a chain block and Sunday afternoon I lifted the lathe off the trailer! I did have to let the tyres down to get enough clearance to pull the trailer out but actually it all went perfectly. I borrowed some 1/2″ OD stainless rods that we’d had in an auction lot through work and dropped it onto those.
Once down I screwed an anchorage into the floor of the workshop and used the chain block again to drag it in, moving the rollers as necessary. It took a while but it’s now in position. Very satisfying.

Now I just need to get it to work...
Now I just need to get it to work…

I spent an hour or so last night cleaning, lubricating and inspecting it and can see there’s a bit of work necessary. There’s definitely wear on the tenons and the bed but I’m sure that I’ll be able to get it good enough for general work.

The lathe installation

It’s going to take me a few weeks to get to the point of it actually working but the next step is to actually get it into the workshop. It’s not that easy a thing to do, since the lathe isn’t exactly light but since it was such a lovely day, I thought I’d spend it cobbling together a gantry out of the half rotten pile of decking we removed from our garden at the end of last year. I’m loathe to post a picture lest the whole thing collapse tomorrow when I try to lift the lathe… but I’ll be optimistic!
I did think about hiring one, but I could well do with saving what I can for fixing bikes and trying to do some racing this year. I’ll post pictures tomorrow if it’s a success and if it isn’t I’ll pretend nothing happened.

The weekend’s spoils

The main point of this weekend was to go up to Worcester to pick up the lathe that I bought from a fuzzy picture on ebay. It’s a Smart and Brown Model M Mk2 toolmakers lathe from the 1950s and is soon to be manhandled (400kg?) into my little workshop. I’m going to need to get a phase converter as it’s three phase but I am really pleased. I think you can get much more for your money if you buy three phase.

It looks better blurred...
It looks better blurred…
This cost me less than £200 (although a phase converter will probably cost as much). It’s a proper little tool-room lathe and it’s got collets and a three jaw chuck. I’ll just have to start picking bits of tooling up here and there and hope the thing works when it’s all in.

Also, I went up to see my dad to pick up my Scott racer’s cylinder block which he’s had to inspect. I thought I’d bring a few more Triumph bits down too but what I didn’t figure on bringing down was another bike; A Silk Scott.

Ten years ago or more, he bought this Silk Scott from Roy Lambert (not the late John Underhill as I had originally thought. Apparently John had owned it and sold it on previously).

The Silk Scott had been George Silk’s first incarnation of a Scott based motorcycle and had applied 1970’s two stroke tuning theory to the ports and the pipe of an otherwise pretty standard Scott engine. The cranks had been improved and the crank chamber sealing was done with a conventional rubber seal instead of the spring loaded metal to metal gland seal that the original Scott design used. He also created a better oil pump using, I believe, a modified best and lloyd pump design from the vintage period. He had a frame made for it out of Reynolds 531 by Bob Stevenson at Spondon which was basically a copy of the frames Spondon made for the small Yamaha racing bikes.

Yamaha AS-1
Yamaha AS-1

Here’s a picture of the Silk Scott prototype.

Silk Scott prototype

The road bike’s rolling chassis was finished with Spondon 38mm forks, a single sided twin leading shoe front drum and a mechanical disk on the rear. Aluminium rims and a light alloy tank certainly kept the weight down here at least.

Basically it’s a complete racing chassis, built to house an engine which had changed very little from 1928.

The soon-to-be Moss Silk Scott racer!
The soon-to-be Moss Silk Scott racer!

George undoubtedly released more power from the engine, but at a cost. Scotts are not a ‘Schnuerle loop scavenge‘ engine, they are a crossflow engine with the exhaust port and transfer ports opposite each other in the cylinder and using a deflector on top of the piston to send the transferred inlet gas into the top of the combustion chamber, thus scavenging the cylinder.

Deflector piston
Deflector piston

The Scott is notable as a two stroke for having a great amount of torque at low revs, probably because the design does not depend so much on gas velocity to achieve a decent scavenge. Loop scavenge engines, with the transfer ports adjacent to the exhaust port can be susceptible to losing charge directly through the exhaust if the revs aren’t high enough. There are other factors at play, but the torque of the deflector piston Scott really surprises people used to later loop scavenge designs.
If however, as is often done when tuning a loop scavenge engine for greater power, you raise the exhaust port and the transfer and extend the inlet duration, you tend to lose the bottom end. Maybe that’s ok when you’re able to get a engine producing a significant amount of power a bit higher up the rev range, but Scotts aren’t so keen to rev with that massive hump on top of the piston and also have completely unbalanced cranks, relying only on flywheel damping.
Plus the fact that the standard (long stroke) Scott only ever had a three speed box, and the Silk Scott only a four speed box doesn’t enable you to cover a narrower powerband and you start to see where modifications to the original design require an overall consideration of how these things link with each other.

Our plan is to build the Silk up with one of my dads racing engines, which only slight differences to the original port timings but has much better gas flow, and work to make a decent set of exhaust pipes to exploit the low rev range available.

We originally planned to make the Silk Scott a test bed for the engines we built for people so we modified the frame with the intention of doing a detachable front cradle to aid engine swapping.

It’s going to be tight to get it done this year, but I’m going to get on with it and see how it goes.