Valve job with head gasket replacement?

66fs said

I do not agree with his thinking. Every valve job sinks the valves, which looses power. There are a lot of parts that "mate" together. Guides, retainers, locks, springs, seals, and valves. Are you willing to replace them all? Lapping is an easy way to check seal. If it does not have a "good" valve job then it should be done, we are talking about a Performance engine. What bothers me is why did the head gasket blow? I always milled the heads flat and never had a head gasket problem after.

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That's untrue. It's all dependent on how good the valve faces and seats are. Lots of times you can simply get by with lapping the valves back in, which removes essentially nothing. All it does is assure the there is a good seal between the valve face and seat. Even with mild pitting on the exhaust, you can lap valves back in where the seal is good without sinking them one iota.

Only when the surfaces need grinding or cutting is there any material removed and even in that instance, it can be a very light cut. I only removed what was totally 100% necessary when I was doing head work. Sometimes as little as .003", plus lapping. You will never see a reduction in power from that. We never did excessive cutting or grinding, because if they didn't clean up with a light cut, either the valves, seats or both needed replacing.

It is a fact, most people see a power increase, because now the valves are sealing again 100%, plus having the heads redone probably includes a light mill to restore a flat surface and that would negate any small amount the valves were sunk, if at all.