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snowman snowman is offline
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Join Date: Feb 2003
Location: So California
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Originally posted by Mark McClure
I have been under the impression that lapping in valves is a way of reseating them in the seat. The more you lap the lower the valve is seated and the more the face is matched.

The valve seat, in the case of a 3 angle grind is say 0.050" wide, the valve face is approx 2 to 3 times as wide, eg 0.150" wide. Consequently there will be a ring of contact on the valve face that is 0.050" wide, usually near the outter third of the valve face. If the valves are lapped properly they will define a ring or groove that does not have any ridges inside of the contact area, but there will be a sharp step both on the top and bottom of the contact area. They will seal perfactly untill the temperature changes and like I stated before the vavle gets longer, the seat larger in diameter and you now have the contact surfaces sitting on top of one of these ridges. Valve manufacturers send out info on this to machine shops that include a good picture of what is happening

Last edited by snowman; 05-19-2005 at 02:59 PM..
Old 05-19-2005, 02:16 PM
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