inline 4 cylinder 2 stroke engine?

[Bryan H]

Something like this perhaps.

RD AC based crankcases, Zegers cylinders and Rennstar heads

[Dvsrd]

btw tz500 is a 4 cyl, not a 3.

Yes, I am fully aware of that. Maybe I should have called it a "TZ 500" to avoid confusion. In any case, that twin with an added crankcase/cylinder was a way to be sort of competitive in the 500 class, with a cheaper and more available TZ250/350 twin. The resulting bike, for all intents and purposes was a "TZ 500 triple"

In any case, I still believe that the easiest and cheapest way to build a big HP 2 stroke multicylinder motorbike, is by using a snowmobile engine. They are more developed than any motorcycle 2 stroke, except perhaps the latest KTM 250/300 and the Bimota V Due. The Tularis was reasonably well engineered and built, although I do not know if it ever was raced for real, though. A Polaris or Arctic Cat Triple, a Yamaha 4, or even a Ski-Doo twin all have a lot of HP in stock trim. I guess jetski engines are pretty similar, except for being sea water cooled.

[Dvsrd]

TZ250/350 with an extra cylinder grafted on was actually a pretty common mod before the 500/750 came out.

Interesting. That one I saw on Phillip Island was the first I ever heard of. Makes me wonder how the crankshaft/primary drive/clutch/gear box holds up with an additional 50% of torque. And even more on Millyard's 5 cyl Kawasakis.
Yamaha definitely did not come up with the TZ750 architecture with a layshaft, and 2 separate crankshaft for no good reason.

[teazer]

That was probably Hinto.  At one point, I lived less than a mill from one of the Hintons with a garage full of Manx Norton parts.  Famous racing family.  Or was Rob Hinton's bike Air cooled?  Too long ago to remember.

Karel Zegers built a triple back in the day that was very fast.  He used to have a Yamaha tuning shop in Melbourne. Last I heard, he had moved up bush and was out of bikes. When I bought my first TZs and RD400 motor in a TD3 frame I talked to him about doing some modifications but my budget was too slim.  Some things never change.......

[sav0r]

The problem with snowmobile engines is that they are designed to run a very narrow RPM range, which is what contributes to those insane max numbers. They just aren't all that friendly for road racing, or roads, or much of anything outside of their intended purpose. There is a formula car class that started with 440cc Rotax engines, later upped to 500cc engines, and they keep the snowmobile clutch. The are wicked fast for the price. Watching them try to drive in the rain however is almost laughable. Even with giant rear tires relative to a motorcycle the cars run at basically 100% torque all the time and as a result are uncontrollable. I can't imagine trying the same thing with a motorcycle. I suppose with some work the cylinders and heads could be adjusted to work butter, but it would take significant work. Two inline twins (side by side with mated cranks) with rotary valves remain the gold standard IMO, starting with something like a Rotax 256 or a modern variant is the way to go, and the packaging fits in a motorcycle. I was hunting inline twins for some time, the best offer i got was $6500 for a single motor out of Canada. The power valves are servo operated, it uses a real ECU despite being carbureted, and it should make around 115hp out of 250cc. At the time I couldn't really swallow the price so I passed. But 230hp out of 500cc sounds pretty good. Maybe not MotoGP (500cc) level, but pretty damn good.

[economan]

Might that be  BRC Racing.  ?   Really cool 2 strokes engines, karts & dirt bikes.

[rodneya]

Why would anyone bother to try and make something out of sleds or vinatge parts.

Go with banshee parts and you have a huge selection of oem and aftermarket parts available. Billet cases, billet cranks, billet transmission parts, upgraded clutch options, a large selection of exhausts and cylinders to get the displacement and the type of power you want.

[Gil Gallad]

i just want to make an inline 4 cylinder gt500. thanks for ALL the suggestions. i thought the place with the new crankcases looked a good bet, but i messaged them a week ago and still no answer. obviously they aint interested  :evil2: i'll keep looking and asking [daft] questions, but as long as the old bloke with the scythe doesn't come calling, then i will build it. oh yes, i'll want to put the ramair covers on as well. got to look like a proper gt500  [apart from the gt500 twin, which for some reason never had them]   ;D
cheers, gil.

[RD7]

Gill I did a quick google of GT250 cases and from a cursory inspection they share a lot of similarity with RD ones.

I don't think it would be too hard to make a four, a mate and I built a four cylinder Yamaha by cutting and welding cases and it really wasn't that problematic.

I would enjoy watching it being build so please  do start a thread.

If you have any questions about what we did ask and I will try to answer.

[Gil Gallad]

many thanks rd7 and everybody else  8)
as soon as i've finished the gt350 [347cc] suzuki engine in the kawasaki gpx250 rolling chassis project, i might just start that one. unfortunately rd250 cases aren't that common for sale over here, and pricey, but i'll bear it in mind  ;D
cheers, gil.

[sav0r]

You could also start with 100cc or 125cc karting motors and mate them to a transmission. I drafted up a motor like this and may still do it as I have quite a number of 100cc water cooled karting engines that basically paper weights these days. I figured an EX250 transmission would be a good fit because they are readily available and light weight given the lack of torque a 2-stroke will produce.

[rodneya]

Looks like this guy turned his dream into reality