trucker3495
New member
How much air pressure is applied for this test?
Testers differ but normally a 100psi source will suffice.How much air pressure is applied for this test?
Sneaks, there’s no “But”, that’s exactly what “I” said.I don't disagree with Al if your at the track. But at the shop/garage a leakdown can diagnose a problem more specifically than a compression test.
Usually due to the constant re-formulation of gas and the removal of lead causing manufacturers to keep reformulating the valve and valve seat materials In other words they keep screwin with our gas so they can make more money by making it cheaper-- no matter what anybody tells you!!!I find that new valves will leak down about 8-10 percent but after a day of running/breaking in, they will seal completely.
However, I have had a few heads that were good but after a season or two they would no longer seal. When re-cutting the seat, the angle has changed; not sure whether it was the valve guide or the seat.
They still Do My quote was from Neways newest info. As far as the interference fit and run in goesNeway used to discourage lapping they preferred that you allowed the valve and seat to run right off their cutters and they would peen themselves to a perfect seal. I must admit after cutting I always lapped, I just couldn't bring myself to putting the head on an engine knowing there was leakage.
I made a plate and threaded it with the head bolt pattern then I made a gasket out of gasket material, I torque the head down per spec and check the head assembly only. When I build our motors I cut the seats, lap the valves and then do a leak down on the head only, I make sure it is sealed with zero leakage before I finish my build.