1980 250cc -> 390cc, bolt-on?

Good evening!

I cracked an engine case and will be looking at a complete overhaul, so I was wondering if the 390cc topend is a direct bolt-on to a 250cc bottom-end?

According to the parts manual I'd say so, but I could be wrong?

No, The 1980 250/390 cases are the same but the 250 crank will not work with the 390 top end.

Marty

Look for a crank for a 390 between 1977 to 1980 as they all have the 71mm stroke you need. Depending on what crank you get, you may need to swap stub ends to match your primary gear inside taper and the rotor of your ignition flywheel.

I have found a 1978 crank. Would I be able to use the stubs from my CR250 crank?

Yes, you can swap stub shafts. The 390 crank's clutch side will be the same as the 250's so you only need to swap the mag side stub shaft.

Marty