yamaha rd250 frame with 400 engine

[rd400greenhorn]

hi guys
is there any problem in doing so? its because i have a old stock rd250 frame, but mainly 400 engine parts. thinking about maybe making a 400 out of a 250 frame, is there any issues with that?
mount rd400 triple tree and 400 fork legs and basically make it a 400?

those are the only 2 differences or? engine capasity and fork legs

[scully]

I think it will work, but you can't remove/install engine with the heads on.

[SoCal250]

Is the 250 an early one ('73-'75) or a later Euro version (1A2)? What are the first 3 characters of the serial number on the frame?

Obviously we don't have the 1A2/1A3 versions here, but I'm pretty sure the 250 and 400 use the same frame so it should be a simple conversion. If it's an early 250 it's going to be more challenging since the engine config and mounts are different.

[stresa]

Hans,
the european 250/400 C/D models and 250/400 E/F share the same frames. Same as the older RD250/350 frames are the same.
As you know german TÜV is a bit pedantic but even here we could put the 400 engine in a 250 frame and got that typed. Same if you made a 250 into a 350.
Yamaha had an assessment back in period which made that swap unproblematic.
Regards Uwe

[rd400greenhorn]

Thanks guys

Uwe, yes that sounds good :) Its because i got a Rd250 frame, considering saving it ( getting it road worthy) but mostly have rd400 parts. So🤷‍♂️..

I believe Its a later model 250, but not sure. But frame looks pretty much idebtical to a 400 when eye Balling it

[stresa]

Hans,
easy to see which model it is. First indicator is the frame number and the most obvious the footrest hangers. On the E/F they are attachted near the swingarm pivot. On the C/D the big hanger under the engine. 250/400 are identical on each model beside the frame number
Regards Uwe