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both of my exhaust shim,tappet dropped out and lost what size should I put back in it?

First things first. You best find them. Hardened steel shims will destroy your motor.

I found one of them how can I find out the measurement of it?

You need to find BOTH of them , if they are inside the engine bad things will happen , to measure them you need Digital Calipers like these

http://www.harborfreight.com/6-in-digit ... 61585.html

Or, you can just leave the other shim floating in the engine and keep a video camera on it when you fire it up. We hate to see destroyed bikes, but something planned like running it with a shim floating around may have some entertainment value.

not sure where you have looked but they often end up on the backside of the flywheel. as mentioned DO NOT run this motor until you recover both.