426 Piston

I'm about to embark on a new cam chain installation on my 426, along with an 03 exhuast cam. I'm thinking that since I'll have the top end mostly apart, it wouldn't be too much extra effort to replace the piston, rings, wrist pin, and bearing.

Is this good practice or overkill? I've heard many reports of YZ 400/426 owners replacing pistons and finding out that the original is still intact. On the other hand, I've read many posts where people swear by top end rebuilds every few years just to be safe.

I have an 01 YZ426 that's all original and according to the guy I bought it from it hasn't been ridden hard. It never had the top end apart and never had the valves adjusted. I checked the valves when I bought it in December and they're still within spec (although they're close to the minimum allowable). This leads me to believe the guy I bought it from, that it hasn't been abused.

I'm thinking that since I'll have the top end mostly apart, it wouldn't be too much extra effort to replace the piston, rings, wrist pin, and bearing.
So far, you're wrong about two things.

One, there is no wrist pin bearing. Second, it's quite a bit more work to pull the head and cylinder. Still, rings are cheap, it could probably use a set. If you want, you can have a leak down test done to check how well they're sealing. If you decide on replacing them, replace the wrist pin and clips at the same time. You can decide about the piston when you see it.

Hone the cylinder with a spring ball hone:

http://www.thumpertalk.com/forum/showthread.php?p=4380759#post4380759

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