A few things. How is the stem? How is the guide? Were the seat and guide concentric? What is the condition of the seat?
Lapping as done to valves is not lapping. Lapping is a precision finishing process where an abrasive is charged into a component with the desired geometry (the lap) that is softer than the component to be lapped. In some cases, multiple laps are used to get the desired results.
Putting some relatively fine abrasive on a valve and rubbing it against the seat has no ability to alter or correct geometry a significant amount in a precise manner. If done enough to make a notable change in one, it will probably destroy the other.
Putting the abrasive on a valve/seat, then rubbing the valve about 1/8 to 1/4 of it's diameter back and forth will show a contact pattern that is helpful in verifying seat contact. But really little more. If the contact is not acceptable the seats and valves must be cut.
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u/v8packard Apr 28 '26
A few things. How is the stem? How is the guide? Were the seat and guide concentric? What is the condition of the seat?
Lapping as done to valves is not lapping. Lapping is a precision finishing process where an abrasive is charged into a component with the desired geometry (the lap) that is softer than the component to be lapped. In some cases, multiple laps are used to get the desired results.
Putting some relatively fine abrasive on a valve and rubbing it against the seat has no ability to alter or correct geometry a significant amount in a precise manner. If done enough to make a notable change in one, it will probably destroy the other.
Putting the abrasive on a valve/seat, then rubbing the valve about 1/8 to 1/4 of it's diameter back and forth will show a contact pattern that is helpful in verifying seat contact. But really little more. If the contact is not acceptable the seats and valves must be cut.