Has anyone ever tried swapping the 249cc for a motocross 249 or 449?

 

anything will fit with enough work. probably not worth the effort though unless you already just had all the parts laying around and the skills to fabricate.

 

Are you a very experienced fabricator and welder, or do you have unlimited funds to pay someone else for the job? These types of projects are not impossible, but they are nothing like dropping in a big block V8 Chevy into a vehicle that had a small block V8 Chevy. Everything from chain alignment, output shaft angles, exhaust routing, etc., etc., etc. can be extremely challenging. I'm not trying to throw a wet blanket on your idea here. Anything is doable with enough time, money, and know-how.

Also, have you thought about how a simple steel frame like the KLX which is designed to house a sub-20 horsepower engine will react to a 50 hp monster 450 racing engine?

 

eh, just throw it in there, weld some triangular bars to strengthen the frame. I would suggest having a wrecked 450, then transfer klx250sf parts to the 450 frame, probably easier.

 

Its hard to plate a 450. That would be one reason I would try to stuff in a bigger motor.

 

That was my main reason of thought, I'm in Oregon and you can't place an MX bike so I thought it would be tricky to put a none legal engine on a street legal bike. I think it would be doable but I was mostly wondering if anyone had tried it personally?

 

And the reason you see very little transplanting of engines from different models/bikes is the difficulty I mentioned earlier. I've seen two real transplant cases executed in person during the years of working in a motorcycle shop as a mechanic. For what would appear to be a somewhat straightforward project, there are all manner technical issues to deal with, and that's only if the donor frame and engine are quite compatible to begin with as it pertains to size and fitment. These projects are serious acts of love. The time and money tallied up in a logical sum total is pretty shocking. Doable yes...reasonable, maybe not so much.

It's interesting that shows like Overhaulin', Fast and Loud, and many others can give one the impression that a mechanical pursuit of any kind is done relatively quickly and without too much headache. Heavy editing and big budgets can make anything look easy.

But...I don't say any of this to dissuade anyone from going for it. There are people out there with enough talent, equipment, experience, and tenacity to get it done.

 

Service Honda! They make the bikes Honda should. They take modern frames and install the old 500 two stroke motors in them. They also have a CRF150R chassis and stuff a CRF250R motor in it. That would be a fun bike. I know they are not street legal, but still a good reference.

Honda Junior-R 250, Honda Trail Bike, Honda 2010 Jr. Trail Bike, Motorcycle


Honda 500AF Motocross Bike, Honda 500 Dirt Bike, Competitive Dirt Bike, Racing Bike

 

One of our club members has a servicehonda CR500 engine in a CRF250 frame that they offer. Even in a platform that they build in a few numbers a year, I believe the price was between 12K-14K. Cool bike...big money.

 

Maybe don't go for a 250 or 450 mx motor, there may be a motor with more power that would be a better fit with less fabrication? Could be from honda kawi, yami, suzi, idk. Maybe measure for 'best overall fit' and then decide if it's worth the time.