Ask the Editors: TRX Motor Swaps
Will the smaller motor drop right in?
Yes it will fit, actually with room to spare but if you inquiring whether or not it will require some fabrication to be rideable, the answer is yes.
Even if you could alter the motor mounts enough for a straight-up swap, issues such as the front sprocket location in relation to the swingarm pivot and the front frame spars preventing correct mounting of the head pipe are going to crop up.
And even if you were handy enough with a welder to make these alterations, you would end up with an engine that will struggle to power the beefier chassis. With the abundance of 400EX parts available on the used market, you would probably be better off attempting to repair or rebuild the 400 mill.
Here is an example of a complete 400EX engine (top and bottom), ready to be bolted into the frame, for $899. If you just need a top or bottom end, expect to pay half that amount.
