Can IC Engine Compression Testing with/without Blanks on Inlet and Exhaust Manifolds Quantify Valve Leakage?

[yamoffathoo]

I am considering refurbishing a 200,000 mile 2.4L, 4 cylinder engine sitting in my shop.
Compression testing at 250 rpm yields 90 psig, which increases to 120 psig with 3 squirts of oil in the cylinders, which is below the 140 psig minimum.
To determine whether inlet and exhaust valves are contributing and need lapping, would blanking both manifolds, then each one at a time and recording changes in peak compression numbers yield useful results?
How much compression increase in either valve train would indicate that lapping is required?
Lifter gaps are within specifications, so I am looking for a reason not to disturb them at this time.
Any suggestions would be welcome, thanks.

 

[mfgenggear]

OP
Look into the leak down procedure. Verify at each cylinder in the top dead center from what recall, how ever I have not done it on while .
So research it verify it. Proper equipment is required. Also Pump air in each cylinder at top dead center and then verify if air is passing or leaking in the exhaust manifold, intake, or the oil dip stick. At 200k miles. Possible needs a rering, and valve job.a proper compression verification should be engine not running. And cranked several cycles. If compression jumps after oil squirter , it is compression rings ate worn. High oil combustion, carbon in cylinder, and on spark plugs , worn oil rings. Burn or warped valves will be detected by the leak down test.

 

[yamoffathoo]

mfgenggear,

Compressed air injection and leak down measurements would be heavily influenced by piston ring leakage.
No detectible leaks past the valves would be perfect but how do I decide what is an acceptable leak rate?

 

[CWB1]

The important variable is valve to seat contact area. To check it, apply a bit of dykem to the seats and rotate a valve 10* back&forth is both direction 2-3x. You want a consistent, wide contact area all the way around.

 

[MintJulep]

But seriously, you'll spend more time doing tests and trying to figure out what's good and what's bad than you will to just do a proper job.

Just lap them.