Hey thanks for the tip on using a belt sander! I have the engine out of my truck and although they don't seem to have been leaking my exhaust manifolds were .025" or more out of flat. The center ports were higher than the ends. About an hour with the belt sander and now they are less than .005" from flat.
I was thinking about how much work it would be to fixture them in a milling machine. Or how much money and delay it would cost to take them to the machine shop. This way is much better and the finish and flatness are great. Hopefully after thousands of miles of heat cycles they have settled down and will stay flat, unlike new parts. Cheaper and better than new, I like it!
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