i pulled my heads and decided to lapp the valve i bought both kinds of lapping compound fine and coarse i have ground and ground but they stay dull in the middle with a shiney band on the top and bottom is this ok or should their be no dull spots
Printable View
i pulled my heads and decided to lapp the valve i bought both kinds of lapping compound fine and coarse i have ground and ground but they stay dull in the middle with a shiney band on the top and bottom is this ok or should their be no dull spots
Also on the newer hotter running engines. The seat you see is not where it will be under operating conditions. That is why lapping is only done for checking purposes. Get the valves done correctly and save the grinding compound for Briggs$Stratton..
The head of the valve gets bigger as it gets hot. Modern engines run with the exhaust valve red hot. The seat is then sealing further from the edge, toward the stem. Once the valve seat is "cupped" from the compound and existing wear, it is harder to maintain a good seat. The cupping condition then gets worse and it's new valve time quickly.
You got it!! If you look at any of the factory done small block Chevies, the later stuff anyways. You will see a narrower seat, up more towards the outer edge than they used to be.. I think GM finally got wise and copied Honda's valve jobs.
the dull spots are where the compound is doing its job it sounds to me like you need a valve job grind the valves and the seats sothey are round again the condition you have discribed also sounds like you have worn valve guides. V8 valve job around $100 and bronze guide liners about $75