Valve job with head gasket replacement?

RustyRatRod said
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 and small amount the valves were sunk, if at all.

It is true. The flow is lost from the valve sinking farther into the bowl, not up from the chamber. If you are removing material from the seat you are sinking the valve, even if it is an iota. My comments were aimed at a machinist who wanted to do a valve job no matter what, any excuse will do, to get your money. I agree with lapping and always lap a couple of each valves randomly after a valve job, since it will give you a visual of how good the seal is and the width of the seats. You give an example of how a valve job should be done and will lose almost no power, and gain a lot if the valves were not sealing. It all depends on the frequency of the valve job and how deep the seats are sunk each time.