[curley8788]

if you were to pump air into a cylinder via a compressor then turn the off, should the cylinder hold the psi entirely? i was just wondering because i remember when i was changing my valve springs if i shut off the compressor the psi would drop like 5 pounds a minute or so and i heard the hissing of the air escaping from somewhere... is that normal? the fitting was hand tight on the spark plug by the way...

 

[JIM]

Piston at TDC, valves closed, good tight motor will still have some leakdown. A tight motor is in the 2-3% range. A loose one is over 10%. Even if your valves did not leak one bit, the piston rings do have gaps in them. Air goes right to the crankcase.

 

[curley8788]

Piston at TDC, valves closed, good tight motor will still have some leakdown. A tight motor is in the 2-3% range. A loose one is over 10%. Even if your valves did not leak one bit, the piston rings do have gaps in them. Air goes right to the crankcase.

ok good to hear. it sounded like it was going into the crankcase but i wanted to make sure it wasnt supposed to be 100% leak-free

 

[Schurkey]

Piston at TDC, valves closed, good tight motor will still have some leakdown. A tight motor is in the 2-3% range. A loose one is over 10%. Even if your valves did not leak one bit, the piston rings do have gaps in them. Air goes right to the crankcase.

All depends on the leakdown tester. The tester itself has as much to do with the indicated leakage as the actual amount of cylinder leakage.

A leakdown tester with an unusually small orifice will indicate greater leakage than a tester with a larger orifice.

My Snap-On single-gauge tester rarely finds a cylinder with less than 20% leakage. 40% is not at all uncommon.