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Reamer size for exhaust valve?

Read a post from Rocket Bob where he used ball honed, I have done it and worked extremely well. I believe it was 1/2”, but look for one of his post.
 
Sorry, I can not help with the specific diameter, but after you know what you need, check on a custom, self guided reamer locally (if possible). It has been years ago, but most precision machine shops own a reamer sharpener and can quickly make a custom diameter for you. Since a standard reamer is $50 USD, A $500 seems a bit high.

In the end your situation for time, confidence, and availability will decide. This is an option, not required. No shame in taking the route best for you.

SCARD did a in situ lap for his engine to extend to TBO, carefully evaluate your valve when the face is visible.
 
The lycoming manual specifies three different final IDs for valve guides, based upon engine model (.499, .500, and .501"). Best to check the OH manual and ream to the size specified for your engine. If you use a brush, the size down to one thou is not required. The .500' size is what you want. The valve stem is .494-.495"

Larry
 
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