Replacement Engine for a 2003 WR450 - will other years fit too?

A couple weeks ago my blue-plate WR locked up at highway speeds, but the mechanic only opened it up yesterday. He said 3 valves are broken, the other 2 are bent, and the piston/dome/cylinder are deeply scratched and beaten up. :thumbsup: No little metal bits made it below the piston and he says the rest of the engine looks fine.

He told me my options are to price out all the parts for a new "top end" (I assume that's everything touching the combustion chamber, but the cams etc are fine) or buy a used replacement motor.

So, does anybody know if 2004+ WR450F engines can be swapped with a 2003? i.e. are all the mount points the same, same routing of cables/hoses/exhaust etc? :thumbsup:

Is that even a good idea, or should I just fix what I have? I know very little about engines, but I'm worried "something else" in the engine was bent when things went bad. The bike was at 100km/h in top gear (around 7000RPM) when the piston ate the valve and everything stopped spinning.

And opinions are appreciated, thanks!

The engines from '03 to '06 are a direct swap, however, it sounds like you just need to replace the piston and valves. You can get the cylinder re-honed and coated and have the head milled. All in all, I'd say it would be a lot cheaper, and you could get a bigger bore for more power. I'd look into sending the thing out to Pro Circuit or some place similar...NOT the Yamaha dealer unless you trust the mechanics there implicitly. You actually have a great opportunity to turn the bike into a real beast...SC

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