Author Topic: yamaha rd250 frame with 400 engine  (Read 229 times)

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Offline rd400greenhorn

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yamaha rd250 frame with 400 engine
« on: May 06, 2021, 12:34:33 PM »
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 :umm:

Offline scully

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Re: yamaha rd250 frame with 400 engine
« Reply #1 on: May 06, 2021, 03:30:38 PM »
I think it will work, but you can't remove/install engine with the heads on.

Offline SoCal250

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Re: yamaha rd250 frame with 400 engine
« Reply #2 on: May 06, 2021, 03:46:27 PM »
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.
79 Yamaha RD400F     77 Yamaha RD400D     
75 Yamaha RD250B     75 Yamaha RD200B (project)
75 Yamaha RD125B     75 Yamaha RD125B (project)
89 Yamaha FZR400      05 Yamaha FZ6
91 Yamaha TZR250R    02 Aprilia RS250 Cup (sold)

Offline stresa

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Re: yamaha rd250 frame with 400 engine
« Reply #3 on: May 06, 2021, 04:26:24 PM »
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
1981 Jackson Special 250 race bike,1974 Yamaha RD250 race bike, 1971 Yamaha DS7 street bike
1978 Yamaha RD400 street bike,1975 Yamaha TZ250 race bike, 1989 Honda RS125 race bike
1980 Hejira PE250 race bike, 1975 Daspa TZ350, 1977 Höpfner-TD3
1978 Broadstock F350 sidecar, 1990 Honda RS250 + projects

Offline rd400greenhorn

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Re: yamaha rd250 frame with 400 engine
« Reply #4 on: May 06, 2021, 05:19:47 PM »
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

Offline stresa

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Re: yamaha rd250 frame with 400 engine
« Reply #5 on: May 06, 2021, 06:27:00 PM »
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
1981 Jackson Special 250 race bike,1974 Yamaha RD250 race bike, 1971 Yamaha DS7 street bike
1978 Yamaha RD400 street bike,1975 Yamaha TZ250 race bike, 1989 Honda RS125 race bike
1980 Hejira PE250 race bike, 1975 Daspa TZ350, 1977 Höpfner-TD3
1978 Broadstock F350 sidecar, 1990 Honda RS250 + projects