RD400 Engine in a Air cooled 350 frame

[Karl squire]

I'm sure this has been done RD400 Engine in a 350 frame, has this been done? I was thinking I'd love rebuilding and RD400 Engine I really think the RD400's were fugly especially the gas tank unless its a 79 or 80, but the 400 engines are nice and I was thinking that would be nice in a 350 frame. so have many people done this, is there any obvious reason why that is a bad idea, is it hard to get the 400 engine in the frame?.

[m in sc]

common swap over the years, i had one.

rear upper mount doesn't line up (cam make on that does though) and the charging system is different but otherwise, direct bolt in. dont forget to ground motor since its rubber mounted.

[Karl squire]

common swap over the years, i had one.

rear upper mount doesn't line up (cam make on that does though) and the charging system is different but otherwise, direct bolt in. dont forget to ground motor since its rubber mounted.

will the JL pipes from a 350 work with a 400 in a 350 frame? Engine position is the same ?.

[m in sc]

rear mounts will be a bit off but not much, pretty easy to make it work. the bigger issue is the 400 flanges have a wider bolt pattern but you can slot the flanges to accommodate the 400 . will the pipe themselves work ok? more than likely yes, ive run 400 pipes on 350s and vice versa seem to work just fine but technically not ideal.

[Karl squire]

rear mounts will be a bit off but not much, pretty easy to make it work. the bigger issue is the 400 flanges have a wider bolt pattern but you can slot the flanges to accommodate the 400 . will the pipe themselves work ok? more than likely yes, ive run 400 pipes on 350s and vice versa seem to work just fine but technically not ideal.

Thanks.

[oxford]

the bigger issue is the 400 flanges have a wider bolt pattern but you can slot the flanges to accommodate the 400 .

The JL manifolds I got were already slotted for either 350 or 400 bolt pattern.

[manicmecanic]

I did it twice.
When I was young my caferacer based on a 351 RD350 was often the only vehicle.
When I killed the engine one of the last times I did buy a crashed 1st version RD 400.
 So I thought better riding with the slow 400 engine than walking.
But it wasn't that easy like with the other RD engines.
 Its very long time since that repair,but I remember I couldn't get the engine into the frame in one piece.If I remember right,I left the heads off.Also I found out later I couldn't get the cylinders off,I cut off a little piece of the upper cooling fins at the inner rear edges.
   Also the top rear mount gave me trouble so I just cut it off.
 No good idea,but as said I was in a hurry.
Exhaust was a mix,I used the 400 headers because of the different bolt distance and welded them R 5 style to the stock 350 pots.Only shortened the 400 headers.
 That way-with this hybrid I had one of my funniest summers on my 351.
I didn't change anything else,so carbs,airbox was still the slightly modded 350 stuff.
 Doing the testride I was quite surprised because I hardly recognized the powerband of the 400 mill.With this setup it almost revved like my dead 350 engine before.My friends at those times already were riding LCs and I had no chance with my ac350 to stay in touch on longer straights.
With this setup they could only get rid of me after quite some distance,so it did run a lot better than my 350 engine.
 But the rubber mounted 400 block gave trouble,the exhaust system wasn't made for the shaking 400 block being held rigid stock style.
 I had to refasten it often because of the shaking engine.The missing upper rear mount may have been also not helpful.I took it out again after some 5000 miles because the rubber bushings were totally dead.Then I put in another 400 block with the 4 mounts but shortly after that it caught some dirt in one carb and one piston melted.
 I never got it running again,at those times even pistons were hard to buy and parallel I started working as professionel bike mecanic.