CR top end on a 250r?

[FatBoy Redrider]

I bought a motor from a guy who had Paul Turner build him a motor. He used a cr250r power valve cylinder on it. Everything fits and seems to work but the exhaust flange is smaller. Has anyone ever heard of this conversion or knkow where to find a flange that will allow you to use an R pipe? I guess these motors are found on TT tracks a lot

[NITRO1253]

ive heard of this conversion but from what i understand the powervalve is not active and closed off because the cylinders that are used are a mechanical powervalve. this setup is supposed to give you the most wicked top end possible on a r but have absolutly NO bottom end whatsoever. i think but and not sure the cylinders they use are a 92 or 93, but again i cant remember exactly right now

[FatBoy Redrider]

actually the PV looks to be run from exhaust pressure and should provide a ton of bottom end. i guess i will never know unless i find an exhaust flange.

check your PMs ;)

[killerworm]

I've got a new engine with the cr250 head on it....the guy I bought it from said it keeps cooler than the original R. On top there is an additional port which means you have to do a little splicing with the hoses...nothing too crazy...cost me about $4 at the local harware.

[FatBoy Redrider]

how did you get your pipe to fit on it?

[airheadedduner]

If the powervalve is operated off exhaust then it is an aftermarket cylinder. The 85-91 cylinder bolt onto the R with some case port modification. You need to run the older R crank with the set up. The powervalve also needs to be stuck open. It is a harsh mid to top motor. The pipe and all fits fine.

[FatBoy Redrider]

i believe it is an 86 cr cylinder. Paul Turner built the motor so i'm sure the PV is setup right.

[airheadedduner]

I am 80%, no 99% positive that the CR cylinder is mechanincal driven PV, not exhaust pressure. The newer CRs use electronicly controlled PVs. That is the only way I could think to get a PV to work on an R besides the aftermarket exhaust driven set-ups is the newer CR cylinders are close to the R set up. I think you need to move the studs for the cylinder on the front forward an inch on the cases and it will fit, but you would have to machine the new stud holes perfect. I don't know what crank you would have to use. I would imagine an 86' but I am not sure. Does your cylinder have a bell shaped diaphram abouve the exhaust outlet?? If it does then it is an aftermarket R cylinder, not a CR.

[BigThumper33]

my 98 cr125 has a mech power valve. I would imagine that the cr250 cylinder is as well. With the powervalve shut he should get some good bottem end, and wit it stuck open it should rip up on top end correct?

[airheadedduner]

Originally posted by BigThumper33
my 98 cr125 has a mech power valve. I would imagine that the cr250 cylinder is as well. With the powervalve shut he should get some good bottem end, and wit it stuck open it should rip up on top end correct?
Exactly

What happens is with a PV motor you can port the cylinder very radical yet still reatain good solid low-mid performance. With the PV stuck open it would be a top top top end motor. I don't think they went to the electronic PV till like 01'. I have talked to someone who is working on getting the 01' cylinder grafted on to an R bottom end. That would be sweet but not worth it when it comes down to moding everything uless you already have all the parts.