can anyone tell me what year of rs crankcases will fit in a 21 frame ?

I think they will all fit. But bolting up? Thats another question.

Didn't the early model RS's bolt in? Pre 90 or something? basically before they went to the right hand chain drive. Still may need to do some modifications in terms of mounting points, but at least the drive side would be the same.
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Charles Gallant

thanks for that mate.

the cases type nf-5, so 1988 till 1992 will fit wirh very little work. Its nearly the NSRs, some parts in the engine is KV3 (NSR250), too...
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nsr300se rs250r´05 ns-1rr

As always Fenton, it's not that simple.

Depending on the configuration, you will need to modify the cases for an NSR stator and pickups, but then what flywheel will you use?

The list goes on and on!
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Andy.
NSR-WORLD.COM

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an rs250 for the road it got to be worth the trouble surely ?

You also have the trouble of a gear box and clutch, an NSR one wont just fit in. The output side of the cases are different as well as the nsr clutch and clutch cover wont fit. The water pump will also prove to be trouble as the RS uses a different shaft and tooth form.
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If I have to take the carbs off once more...

i said to andy when we were at the dyno ill get home and start with the silly ideas

If you can get a complete RS motor and electrics then it will be sound, but I bet you are looking at a good £500 for a useable motor.

You won't be able to run lights (without some more modification), but as you saw on Sunday (Stephen & Fontyyy), that's not necessarily a problem.

An RS top-end also needs pistons and rings regularly - probably more so than the F3, else it all goes Pete Tong rapidly.

Don't get me wrong, I'd love an RS motor in an NSR chassis. An NuRSe is one of my "one day" projects, but there is a lot to figure out first, and a lot to learn from the NSR motor first too.
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Andy.
NSR-WORLD.COM

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sounds like it need to be done then mate but like you said " there is a lot to figure out first" i think i best get a job before getting into this one eh .