Lapping Valves

[kingkobra]

What is the best way to check the valve seal after lapping? I've heard that putting gasoline in the ports and checking for leakage is the best way for the do-it-yourselfer.

How long should the gas stay in the ports? Is weepage acceptable after several hours?

Are there better methods?

Thanks.

[Hotfingrs]

Never heard about gas in the ports....but after lapping, you should be able to see an unbroken line all around the seat.....

[speed220mph]

Use kerosene. It's less of a fire hazard, evaporation is no problem, it's less of a fire hazard and kerosene will do the job. Just position the head so it's gasket surface is level so you can fill the combustion chambers.

[DAVID GAGNARD]

King;

I've been told to use gas-kerosene-diesel fuel and even WD-40. I put my heads on V stand combustion chamber down and put fluid into the intake ports and completely cover the valve head to check for leaks.... One shop told me on a standard non-high performance rebuild one drop every five seconds is the most they accept.... On high performance applications they shoot for no drops and only allow a very little "weepage". Then trun the heads over a little and do the same for the exhaust side....

I usually mark any valves that may show leakage and lap them again and then retest....Usually I use gasoline because I have some around if for no other reason....

David

[OZVENOM]

you are on the right track for testing for leakage but dont get too worried about a small weap as as soon as you start the engine it will start bedding the valves even more flatttening all the micro scopic high points and sealing completely .
if you have aleaky valve the best way to see where it is is too use bearing blue or engineers blue . and put a fine coat on the valve and slide it onto the guide and slap it down onto the seat ,
dont turn the valve and then pullit out and check for sealing .
it will show up any points of leakage. i have used this for years on 5 valve motorcycle heads and it works.
hope this helps.

[auto10x]

Lap them in and there should be a thin grey line all the way around the face on the valve, and the seat should all be gray. If so you're all set. As soon as you start the engine they will seat the rest of the way. Don't get to excited about seepage, etc.

I once saw an engine that, when the cylinder was filled with compressed air at TDC, leaked like mad. You could feel and hear air coming out of both the carb and the tail pipe. After some miles it was completely sealed. (Not that that is a recommended practice, but they will self seat even when the seal is practically nonexistant.)
auto10x
Bill