Yamaha TZR YPVS

Well, now that the 95Racer is finished, which is hard to believe in itself, I’ve decided that I want to see what the antidote would be like. 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 Powervalve engine (somewhat special)
• Honda NC35 single sided swinging arm
• Supersport front-end
• Yamaha TZR125 tank
• Self supporting seat unit

How did I arrive at this combination? A good friend had this RGV250 with a bit special YPVS engine sitting in his workshop for some time. Everytime, I went there I asked him about it. As he is too busy and would probably never get it finished, I offered to help and take it off his hands. This is what it looked like gathering dust in his workshop.

Now, I was just going to 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. I really liked the thought of doing something with that engine. It has TZ750 pistons, a TZ250 crank, a close ratio gear box with dry clutch. Ideally, I’d like to put a Cheetah top end on it and take it out to just below 500cc. However, that’s for later. I really want to ride it this summer!

So why move the goal posts? It all started after seeing this TZR 3XV with a Stan Stephens 535cc power valve engine in it. It was really lovely looking and far more modern than the RGV250. So, after some measuring and chassis geometry CAD work, I decided to use a TZR frame. Is easily fits the powervalve engine, has a much sportier geometry than the RGV, looks bang up-to-date, and 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, I am now at this stage. The TZR frame is completely unmodified, although it will be later to fit the engine and rear suspension mounts.

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.

The main chassis specifications (at static sag) are pretty much ideal with this combination:

• Wheelbase = 1368 mm
• Headstock angle = 23.6 degrees
• Trail = 100 mm