Will a 400EX top end bolt on to a 350X bottom end without mods? I know that the heads are a litlle different, but the cases appear to be the same. Also, are the engine mount locations for a 400EX in the same places as on the 350X? My freind bought an 85 350X that was run without oil, and it has a chewed up head. We were just brainstorming the other day about whether or not a 400EX would fit right in. It sure would be sweet to have an electric start 400cc three wheeler to shred the dunes on.

 

No to all your questions - two completely different engines.

A 350X is a closer match to the 250X/300EX series - although the frames in these quads still needs modification to accomodate a 350X engine - so the opposite would also be true.