Vintage Dirt Bike Q & A

Would an 81 CR 450 motor fit, without too much trouble, into a 1980 CR 250 frame? That would be a cool bike to make. Also Can the rear shock on the 81 450 be rebuilt, and is the 125, 250, and 450 of that year the same shock? The rear shock on my 450 is like a pogo stick. Thanks

I had the same idea with a 480 motor cause i have to rebuilt my 250 motor.
I put the case without cylinder into the frame to see if it fits.
The lower motormount will fit with other spacers.
For the front mounting you have to built new plates.
For the back you take the 450/480 mountingfork and put some spacers between it and the swing arm.
the biggest problem is the airbox because of the kickstart housing. You have to cut the airbox or built a new one.
so that•s too much trouble for me now, but I will try it later. I didn•t try cylinder and pipe.
The shock can be rebuilt if you got parts.
250 shock will fit.
b-joe germany

There is a few people here in England that have placed the cr480 into the 1980 cr250 frame real nice bikes, plenty of poke, go for it give it large.

You're crazy! From what I've read, the 450 motor was an unrideable beast!?
I would think the shock from an 81 250 would fit your 450, but don't quote me on that...

In a good working state the monoshock should give at least an equal ride to a twinshock. If if feels like a pogostick it is probebly broken.
The problem is probebly that the oil of te demper is not of te write type or it is leaking internaly. In that case disassembeling and cleaning the shocker might make a difference. It could also be leaking externaly, in that case the oil is all gone.
In- and outgoing demping can be adjusted by putting other resistor plates (I do not know the wright english term) in, so you can always set the bike up. The plates should be specialy made by a specialist I fear.