Top End Rebuild. When to replace?

I recently acquired my 05 450 in October. Switching from a two stroke, I am not sure when I should consider a top-end rebuild. I have a hour meter on the bike, so how many hours should I allow pass before the rebuild. I race about 7, 1 hour long GP's a year and ride aggressively any other time. Thanks, Matt

It will vary from one bike to another based on a bunch of variables. There's no set time. My '03 still doesn't need it. I did replace the cam chain about two months ago, though.

I usually suggest that you go by what you find when you do a valve adjustment. Once the shim size in any valve goes past .20mm smaller than what was in it originally, it's time to replace them. The nitride hard coating on the valve face is worn through at that point, and the valve faces will start to wear rapidly, if they haven't already. Change out the valve springs, too.

Once you're in, you may as well at least inspect inspect the piston and put a new ring set in it. Replacing the piston is probably wise, even if it looks near perfect, but it may not be absolutely necessary.

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