good valve seat question

[azcafe]

Hey All,

I am lapping my valves and they appear to have good seat with no pits on the valve or the head. When I place the valve in its seat and shine a light on the other side I see light come through when I put a flash light up to it. Do I need to keep lapping or will it seal tighter when I put everything back together and get the engine running?

Thanks for the help guys.

James

 

[HooliganCycles]

pour a little gas into the ports and check for leaks, if it leaks fuel into the combustion chamber its not sealing

 

[Jack]

Hey All,

I am lapping my valves and they appear to have good seat with no pits on the valve or the head. When I place the valve in its seat and shine a light on the other side I see light come through when I put a flash light up to it. Do I need to keep lapping or will it seal tighter when I put everything back together and get the engine running?

Thanks for the help guys.

James

This is more of a common problem then most think and no amount of lapping will resolve it. Either the valves or the seats are warp and will have to be professionally re-cut in order for the valve and seat to be concentric providing a good seal. It doesn't cost much to re-cut the valves and seat.

 

[Jack]

pour a little gas into the ports and check for leaks, if it leaks fuel into the combustion chamber its not sealing

If you can see light with valve resting on the seat or the light disappears and re-appears before and after applying pressure to the valve, there is a problem of two culprits.

 

[azcafe]

Thanks for the reply guys. I think I got a little ahead of myself with the question. I installed the valve springs and checked the seat again an no light shined through. I still plan on putting some gas in there as well just to double check. Thanks for the help.

 

[XSLeo]

If the valve stem to guide clearance is too much the valve will wobble a bit sideways. much more noticable without the springs on. This might be why you see light when shining the flashlight in with out the springs.
To check the clearance with out the springs hold the valve open about 3/8 inch and try to move the valve stem sideways and up/down. any movement means the valve stem and or the guide is worn. If very little you can run them ok.
Leo

 

[Jack]

Thanks for the reply guys. I think I got a little ahead of myself with the question. I installed the valve springs and checked the seat again an no light shined through. I still plan on putting some gas in there as well just to double check. Thanks for the help.

Trust me ,if there's light between the valve and seat just with valve resting with no pressure,there'a a warpage problem.You need to have machine shop re-cut seat and try to re-cut the valve face or install new valves with a fresh cut to true the face up.I've ran into this problem more than once when porting the XS head.

 

[HooliganCycles]

Im with jack, thy should seal with no springs installed