Lapping valves

munch

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Greetings, I have a 1982 cb900c and my manual says not to lap the valves as they have a special coating. Hoping someone knows whether this is true or not. News to me. Thanks in advance.
 
True, removing coating you would expose softer metal thus speed up wear and failure.
Proper repair is replace the valves. What is wrong with original valves, not seating properly, rusted...!?
 
I've lapped valves and re-cut valve seats on Honda engines for over 40 years without issue! What I wouldn't do, is reface the valves themselves. If pitting on the valves is minor and can be lapped out by hand in under 10 minute per valve then I'm ok with that. If the pitting is severe or needs more than 10 minutes of lapping by hand, then I replace the valves. Cutting seats is just fine, there's no extra coatings or anything on them, your limit with a shimmed engine is available shim sizes.
 
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