The beginning of a 2-stroke hybrid
Well, now that the 95Racer is in a more or less finished state, which is hard to believe in itself, it was time for a new diversion. This project is very much a personal project and as such will replace some fairly arbitrary choices and decisions. So, having thought about this for some time, this next project will be a road bike. A 2-stroke no less! In brief, it will consist of:
- Yamaha TZR 3MA frame
- Yamaha RD350 Powervalve engine (somewhat modified)
- Honda NC35 single sided swinging arm
- Supersport front-end
- Yamaha TZR125 tank
- Modern bodywork
How did we arrive at this combination? Well, there was this RGV250 with a bit of a special RD350 YPVS engine that had been gathering dust in the back of the workshop for some time. This is what it looked like in its neglected state.
Now, orginallly, the idea was to just finish it off as it really didn't need that much. But, as it does, one thing led to another, and the goal posts kept moving. The engine, being somewhat special deserved something more. It has TZ750 pistons, a TZ250 crank, a close ratio gear box with dry clutch. Eventually, we'd like to put a Cheetah top end on it and take it out to around 500cc. However, that's for later.
So why move the goal posts? It all started after a customer brought us his TZR 3XV with a Stan Stephens 535cc power valve engine in it that we designed and fabricated the expansion chambers for. So, after some measuring and chassis geometry CAD work, we decided to use a TZR frame, but from the earlier 3MA version as it allows for better engine position. The 3XV chassis is too short, really, for the RD350 engines. It also happens to easily accept a NC30/35 single sided swinging arm.
Of course, it needed a modern front end as well, which came from a Kawasaki ZX6-R, but that was more due to availability at a reasonable cost. Most modern radial brake front-ends would work. So, after a bit of chassis geometry analysis using the ever-so-useful "whole bike software" from Tony Foale, and a bit of alteration, the project quickly progressed to this stage. The TZR frame is completely unmodified, although it will be later to fit the engine and rear suspension mounts.
And here is what the chassis design geometry at static sag looks like:
- Wheelbase = 1368 mm
- Headstock angle = 23.6 degrees
- Trail = 100 mm
The swinging arm was a very easy fit. All it needed was a different size bearing in one end, a couple of spacers, and new inner spacer. The 916 wheel needed the centre hole boring out slightly. The front was very similar, just needed a new set of bearings and the stem needed cutting down and rethreading. Then, it was time to check the geometry design in actual metal. And, it turned out to be spot on. We would have been very surprised if it didn't.