Quote:
Originally Posted by 71cadc10
question, are you taking the leakage test with the cylinder under test at TDC ?
I ask because your lowest readings show 5 & 8 which are sister cylinders and both would be at TDC (or BDC) at the same time.
like you noted, the main way air can get from chamber to intake manifold, is intake valve path. However, if the PCV hose is hooked up to intake, this could allow some more to get to the intake from the crankcase. Air bleeding by the ring gaps would then push up thru the PCV and you may hear it in the intake. If this is the case, you should hear it on all 8.
Another check could be remove the intake manifold...pressure up and spray some soapy water directly down the port to see if the intake valve is sealing. You'll get bubbling if the valve seat isn't sealing.
air rushing out the oil fill tube, will happen slightly just from the ring gaps. Large amount of air would indicate larger ring problems. I've done these type of tests before and if the piston was at bottom vs. top I'd get different results.
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Your points are valid. Feeding air pressure to any cylinder with bad rings will cause air pressure to build in the crankcase. That air could then travel from the crankcase, past the bad rings in another cylinder and up through that second cylinder intake valve if it were open.
For all of my leak tests, the PCV and fresh air lines were disconnected from the intake.
I tested cylinder leak by 2 methods.
First method was with rockers properly set. I then rotated the crankshaft and tested leak while the piston was midway up on the compression stroke (valves closed).
Second method was with all rockers loose so all valves would be simultaneously closed at all times and with every test. Results were almost identical.
The second method would be the most reliable way to test for any valve leak.
I suspect out of round cylinders or broken rings, or both.