Yamaha TZR YPVS

This project has been lingering for a long while now. It’s been difficult finding time to spend on it, yet I am really wanting to as it will be my only road bike! I’ve sworn to myself that I’ll get out on this summer. I really miss riding on the roads these days for some reason. Oh, I know why, I am not getting enough race miles in either.

The engine has been completely rebuilt, both cosmetically and mechanically. The main reason for re-doing the engine was to strip the cases and cylinders of paint as I prefer the vapour blasted bare aluminium look. That was quite a bit of work in itself. The other reason was to measure all of the engine parameters, such as port dimensions, timing, etc. I intend to model this engine and design pipes and inlet tract based on detailed engine simultion. This approach has been so successful on the 95Racer project. It’s been quite some time since I worked on a 2-stroke engine and I had forgotten how simple these things really are.

The most amount of work has been on the chassis, though. Front suspension was pretty much a bolt-on aside from a modified stem and new bearings. It’s off a Kawasaki ZX-6R 2004. Like on the 95Racer which uses 2006 Yamaha R6 forks, the ZX-6R forks are too long as you can see in the picture below. I’ll shorten them eventually like on the 95Racer but will leave them for now in order to get it on the road sooner.

The rear swinging arm and suspension are finished with new frame attachment points and adjustable ride height. The swinging arm is off a Honda NC35 and fitting it was surprisingly easy. All it really took was a couple of spacers and new bearings. The new suspension again was designed using Tony Foale’s excellent chassis software, which I’ve now used on over 20 projects. Every time the results have been extremely pleasing. The shock is Proflex unit rebuilt to new. I intend to adapt the remote reservoir to a piggyback unit, but again this can wait until winter.

As Intended, the engine is suspended in the frame using the original 3MA front mounts with new brackets that bolt to the bottom of the cylinders. The rear mount is standard YPVS welded on in the appropriate location. As you can see, there is no front subframe, nor any stabiliser bars. I am fairly confident this will work OK to contain engine vibrations, based on the many YPVS engine transplants we’ve done. We’ll see when we run it in, in hopefully about 4 weeks.

Engine has TZ350 magnesium cases with dry clutch and close ratio box. Displacement is 375 cc with TZ750 pistons. Radiator is a TZ350 race item and I am using another electric water pump like on my 95Racer. This is mainly for packaging reasons as otherwise I’d have to cut to much from the fairing. Nothing wrong with the standard TZ350 water pump (available here), except it will save about 1.2 kg.

The other main area receiving some attention of recent is the body work. I’ve decided to use Yamaha YZF-R125 body work. I looked long and hard for something that looks modern, OEM looking, but nothing too wide like most 600’s. I also didn’t want the usual 205 race body work such as Tyga, TZ250, etc. There are side panels which are not fitted for these pictures, but you’ll see what they look like if you look at the standard YZF-R125. It turns out that it fits the 3MA frame really well. The biggest job was adapting the nose cone stay to the frame mount, but not too difficult. A bit of cutting and it goes on easily. The tank is still the plastic TZR125 tank. The tail section will also be YZF-R125 as soon as I get the chance to make a rear subframe.

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