Engine swap suggestions for Yz400f chassis for trail bike?

Seems like the majority likes the idea of a yz/it465 engine swap.

It would be a really cool project. I remember those bikes having torque to be able to walk up anything, but a bitch to start....

IMHO, if you stuff a large 2 stroke in it, it will be a handfull. For sure it will be a very powerful, fun bike, but it will still be a handfull to ride.

I am liking this engine swap idea though. I'm a bit of a gearhead so I'm always thinking about things like this.

Other more practical concerns...

You need to make sure that the swingarm pivot is going to be relatively compatible. It will be much easier to accomplish if the swingarm pivot area on the engine is both narrower and larger in diameter. Modifying the swingarm for a wider engine would be a pain at the minimum, and probably dangerous.

If you go with an air cooled engine, the gas tank fitment might be a bit of an issue with the fins protruding upwards towards the tank.

On the older big two strokes, the expansion chamber comes up way high, and there's no way its going to work with the tank and shrouds (guess you wouldn't be needing the shrouds though) on the yz400. You could probably modify a cr500 or kx500 exhaust system to fit.

Do you know how to weld? Do you have a welder? Would you be open to other make swaps, like a cr or kx or ktm engine? From what I've read anyway, the later cr500's are supposedly more ridable. Just throwing out ideas here.

Super Hunky did a swap with an air cooled RM250 motor in a 2000 YZ426 frame and did a huge writeup here: http://www.off-road.com/dirtbike/projects.html. Good read.

Although it may not physically fit, I'd love to see an XT/TT/SR 500 motor in a modern chassis. You can get some info (i.e. physical dimensions, etc.) from the Thumper talk vintage forum if you ask there.

Good luck,


The write up of that engine swap was done quite nicely, and shows you some things that you will need to watch out for if you embark on a swap. However, as nice as the write up was, I don't think the quality of work was very good. There were a lot of things that just seemed rushed. That engine swap build highlights a ton of things you shouldn't do. Sorry, but I think it was a bit of a hack job.

For instance, drilling out all of the mounts to larger sizes to "increase strength" in fact probably made things weaker. Instead of taking the time to fabricate and weld mounts, the ignition system was just zip-tied into place. Painting over the engine and frame with black paint, without bothering to first strip down the old paint looks less than pleasing. Lastly, the exhaust setup wasn't properly mounted, and lets be honest; one of the worst things about those old 2 strokes was the exhaust that was routed down below the frame.

Its clear that the author put in a lot of work, and I applaud the effort, but all of those details is what really makes the difference in a swap of this sort. If you're going to embark on a retrofit project, be sure to think about all of those little details, because they will be the difference between something that looks cobbled together and something that looks factory-installed.

For anybody looking to do any serious fabrication work, please see this website: www.mcmaster.com

Mcmaster has every kind of mechanical device you can think of, and the prices are reasonable. Screws, washers, shims, metal stock, bushings, not to mention anything else you could ever think of. They have it.

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