Whilst I work out the port timing calcs, here’s a very early picture of Roger’s Flying Squirrel racer frame to illustrate his description in the comments to the post ‘The evolution of the Super Squirrel racer’
The crankcase in this shot is, I believe the last standard Scott case that he ever used but fitted with the four bearing crank he made to help stem the tide of standard longstroke overhung crank induced engine carnage. Note the odd shape of the doors with the bolts in the middle. These are just blanking bolts; once removed a slide hammer can be attached to the doors to extract them as they obviously have to be a good fit to support the crank assembly.
The strength of the crank assembly was proven in quite extreme circumstances when there he started it at a meeting and it fired on one before hydraulic locking on the other cylinder, in which there had been a water leak. The contest of strengths was lost by the crankcase, which split across the main bearings. So much for sorting the crank problem.
Another interesting thing to note is the blind head block, which I believe was aluminium. This didn’t have any kind of higher compression inducing form work in the top to match the pistons, as his detachable heads do, but it would have been lighter than standard and running Silk pistons as we still do now.
just found some photos of the whole assembly:
Also here’s a picture of him working machining a crankcase for Ted Parkin’s Scott. I believe this has extra large doors to take a set of special extra long stroke cranks.
and here is Ted’s racer with new engine in place.
Ah Yes! happy memories! When I was racing what would now be termed Superbikes in the 70’s, I was asked by Jack Glover, owner of Granby Motors of lkeston, if I could recondition some Yamaha TZ barrels. Jack was running a race team with TZ bikes and they were finding that the barrels were not lasting very long and replacements were expensive. I agreed to have a try as our family firm Moss Machine Tools had a good team of engineers and plant, including an excellent pair of Italian Nova internal grinding machines which would swing up to 26″ diameter. The first job was to grind out the existing chrome plating on the aluminium bores. We quickly found that it was intended that the finished thickness should be 0.004″ (0.10mm)
However, intention and actuality were not always the same thing, as I found examples where there was 0.001″ on one side and 0.007″ on the other side. At this point, perhaps it is pertinent to make comment about the thickness and material.
It was necessary to achieve a finished chrome surface thickness after grinding of 0.004″ as the operational optimum because if the film were to be much thinner, then there could be the possibility of ingested fine hard dust particles digging in and fetching off the thin film . If the chrome was much thicker, then it became stiffer and brittle and under the slight changes as the barrel heated and cooled, it could develop cracks that could lead to sections becoming detached. The real trick was to establish reliable datum faces and clocking registers that you could use to accurately re position the block after re chroming in order to regrind accurately to end up with the optimum equal thickness of chrome. The old chrome was removed by grinding the bores and the old chrome remove from port edges so the new chrome could go round the corner of the ports for security. Chroming was done by Michrome of Hinckley in a process they term “Sinchromel” Our older readers will remember that the TZ did not compromise power by fitting air filters and thus it was accepted that fine dust could enter the engine. The chrome lining is quite robust and can tolerate this and works well in such situations. I am often asked why I did not use a more modern surface coating of the Nickasil type.
The reason for this much thinner coating being used, is that it can be applied quite evenly and so does not need the expensive grinding processes. The proviso is that it is prudent to use with good inlet filtration. Naturally I applied this experience to the Scott blind barrels until the VMCC re defined the date up to which a bike was considered “Vintage. It had hitherto been December 31st 1930, but it was changed to Dec 31st 1934.
This was a gift to Scott owners, as in this year the engine style was changed from having a one piece head and barrel (A blind head type) to have a separate barrel and aluminium cylinder head. This enabled me to have made patterns for casting heads which had the mirror image shape of the piston deflector incorporated into the cylinder head and then the actual combustion was in a small central chamber to some degree following the philosophy of Ricardo. This certainly helped a more even and faster burn as proved by the fact that the optimum point of ignition was retarded step by step as the experiments progressed. In 1997, I was asked by Brian Lilley, then running the SOC Spare Scheme, if I could make some “Unbreakable cranks” and investigations led me to source 300M VAR from the USA which has a strength in the state I use it of 110TT with excellent resistance to alternating stress fatigue. This was a gift for Scott owners as the primitive metallurgy of the traditional case hardened cranks has a finite life, (just as we do) but this material is never taxed anywhere its critical loading to register as reducing its fatigue life. The four bearing crank set has been replaced with components in 300M but with Tungsten heavy metal weighting slugs to alleviate the out of balance of the basic design. The flywheel also has a weight ring added to make the engine run more smoothly.
I really should get on with some work now, but before I do, I will share an amusing and thought provoking episode with you.
I had had my first batch of high strength cranks machined in California, so I could be sure of using the specialist heat treatment plant that did such work for military projects. There is no job so well produced as cannot be rendered almost useless by bad heat treatment. I know from personal experience as I was responsible for a heat treatment plant in the past. The parts were im,ported and I ground them up at South Croxton. I then decided that I should have them “Blackodised” This gives a nice black corrosion resistant finish, so off they went to the processors. A few days later I received an anguished phone call. Roger we cannot get these parts to go black. We have replaced our vat chemicals with new and they still will not go black. We are out of ideas, do you have any ideas. I laughed heartily, to which Steve Lane, for it was he, said, don’t laugh Roger, this is our trade and this is serious. OK Steve, I replied, I understand and I will explain it thus. There is nothing in this life that is really solid. Everything is made up of atoms with electrons etc. whizzing round in circles like miniature Solar Systems. Now I ask you to imagine in your mind’s eye, a bar of Aero Chocolate and look at the filling with lots of little holes in it. Well, this you can equate to the steel you are used to processing. Now imagine you have broken a bar of good quality dark chocolate and the texture is, to the naked eye, devoid of such holes. Well this equates to the special steel these cranks are made from. You see, not only has it been made from the very best ingredients, but it also had an extra process called Vacuum Arc Remelting that much refines its structure. The result is that the steel is so dense that the black die that is part of your process, will not penetrate as with a normal commercial steel. What do they look like Steve? Well Roger they are a mid brown. OK Steve, that will be just fine and the colour will just prove that this is a steel of a vastly different quality to that usually used in commerce, but then Steve, we needed something that was a quantum leap forward in its fortitude to give our Scotts the stamina they deserve for the future. OK boss, can I go now?