rdoactive

Years ago I always heard leak down tests being done at 100 psi. Of course, it's easy to turn over the motor if it's not exactly at TDC with 100psi. But then again, they might have used 100 because it's easy to figure the percentage.
The leak tester I bought years ago operated at 40psi. I figured they decreased it so the motor wouldn't spin, liability issues, whatever.
I just looked at one today that operates at 20psi.
Does it really matter what psi they run at?
Gary

stevesxm

yes. the lower press ones don't give nearly the accuracy and resolution as those done at hi pressure. i think 20 psi is a waste of time. i think 40 is so borderline as to be meaningless. at 100 if the piston is slightly rocked you know it immediatly and get to position it properly so you get a good and accurate result.

Strip Poker 388

iTrader: (6)

I like the 100psi better,I would also think the lower psi one accuracy would be to much of a varance .This is what I use

http://www.pingelonline.com/images/E...st%20large.jpg

czy40p

How do you perform a leak down test?
What can you tell from it?

rdoactive

Set your cylinder TDC, compression stroke, warmed engine.
Hook up your tester to that cylinders spark pulg hole and a compressor.
Scale on the tester tells how much leakage there is in a cylinder.
Listen to the oil breather for air hissing (leakage by rings) or water jacket (leakage from head gasket, cracked head) carb (intake valve), exhaust (exhaust valve).
Gary

czy40p

Thanks, I have heard that is the best way to check the condition of an engine while it is still together, but was not sure how to do it. If you do not mind, how do you determine when each piston is at TDC?

Jim

rdoactive

Remove the distributor cap. Whach the rotor till it gets to the appropriate cylinder plug wire.
this is close enough to insure both valves will be closed. But 100psi will crank the motor if it's not exactly at TDC. So you can use less pressure (40psi) or use a breaker bar to lock the crank in place.
Gary

czy40p

Thanks!!

Jim