Jump to content

RM250 '90 engine | max. bore and stroke?

Recommended Posts



I got a nice deal of a '90 RM250 engine.. just curious, if I could build a bored&stroked RM250 engine with about 400cc displacement (79,7x80mm | bore x stroke).


But first I need some measurements..

-cylinder sleeves thickness? Or just the maximum bore diameter for stock cylinder. I know the cylinder is nicasil plated and I can get it re-plated for quite cheap.

-How much space is in the crankshaft? The stroke would be increased 8mm IF I decide to build the engine with 79,7x80mm bore x stroke.

-Deck height; negative or positive? If it's positive (= the piston doesn't reach the top of the cylinder or go over it), then it'll be a lot easier to get the timing correct with 80mm stroke


Also, I've been thinking about piston speed.. in stock condition the engine revs up to 9,500-10,000rpm. Piston speed @10,000rpm is about 24,0m/s.

That's a bit too much.. so with 80mm stroke the engine would rev safely up to 8,500rpm.



Feel free to critize, comment and suggest. I have already build a bored&stroked 50cc moped engine, so this isn't new for me.


Edited by RM<3
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

  • Create New...