valve lapping

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TonyM

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If concentricity is ensured by the machining process with a decent surface finish then grinding is a waste of time and effort. The seat and the bore are machined from the same end without removing from the chuck and the seat and stem are machined without removing from the chuck. I have only found it necessary to lap valves on old(full size) engines where the seat or the valve has been replaced or re-cut or where there is some pitting.
 

scooby

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ok I'm going to loctite new valve cages in and re drill intake/exhaust paths. Will test with pressure through spark plug hole like before.
If concentricity is ensured by the machining process with a decent surface finish then grinding is a waste of time and effort. The seat and the bore are machined from the same end without removing from the chuck and the seat and stem are machined without removing from the chuck. I have only found it necessary to lap valves on old(full size) engines where the seat or the valve has been replaced or re-cut or where there is some pitting.
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Steamchick

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The intention of lapping valves is not to make an eccentric valve align with the seat, but to improve the surface finish of the machined surfaces. If the machined surfaces are a fine finish and high degree of concentricity, then the seat will be perfect as machined. But when grind - stones are mounted on a mandril to grind the seats in industrial applications the ground surface is too coarse and needs lapping to get a finer surface finish. My opinion is that 1000 grit is OK, but that is only because that is the finest grit I have...
My Moto Guzzi workshop manual gives seats machined at 89 degrees internal angle and valves at 90 degrees internal angle, then intersection of the 2 cones is lapped to 0.5 ~ 1mm wide. But that is on valves 28 ~ 30mm diameter.
Hope this is of some use?
K2
 

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