Compression / Leakdown Results
 

Just got my compression and leakdown results: 123k 1982 SC

leakdown >
#1=4%
#2=43% (ouch)
#3=6%
#4=30% (ouch)
#5=4%
#6=15% (hurts some)

compression >
#1=140psi
#2=110psi
#3=140psi
#4=130psi
#5=140psi
#6=140psi

So ... these numbers indicate that I need a top end rebuild...correct?

and while you are in there .................

Just a thought,

The leak test is usually done in firing order: 1-6-2-4-3-5.

Is it a coincidence the high leak cylinders are -6-2-4-?

1-6-2-4-3-5

It isn’t one bank. Could the tester been out of adjustment for three consecutive measurements?

Best,
Grady

Grady >
Exactly why I posted the results. This is the first compression/leakdown test I have ever had done - therefore, I really don't know much about them.

We did the test b/c I am getting puffs of smoke at high rpms between shifts.

Is it possible that the tests are wrong?

Puffs of smoke often suggest worn valve guides.

Leakdown tests should be reconfirmed, and should be accompanied by listening. Crankcase hiss is rings. Intake hiss is intake valve. Exhaust hiss is exhaust valve.

It takes so long to remove, disassemble, machine, reassemble and reinstall an engine, that it makes sense to invest some time in diagnostics.

Craig,
A leak down test is more than some numbers. Unless accompanied by where the air went, you got a half-test. Kind of like using a volt meter and not reading the result.
The results from cylinder 2, if confirmed, is enough to tear down your motor.
So where did the air into cylinder 2 go?

Craig,

Never make an important decision like this based on one test - - or even two and more.

Are the sparkplugs in good condition? Was there any significant variation among them? If OK, put the plugs back in and take it for a nice pleasant extended drive early some morning.

Repeat the cylinder leak test going around the firing order twice (two tests per cylinder). At each test listen for the leak hiss (there always will be some.) A good tool is a Craftsman stethoscope. Use the open end of the stethoscope hose in the intake (past the sensor plate with the throttle wide open), in the exhaust pipe (pretending you’re a proctologist), in the oil sump tank and at the junction of the head and cylinder underneath. Good cylinders will usually have some leakage (2-6% depending on gauge) past the rings and hear it in the sump tank.

If you have significant leakage past a valve, remove the valve cover and check the valve clearance. If the clearance is OK, take a soft mallet and strike the adjuster in the rocker arm. Do this while the cylinder is pressurized. See if the leak measurement changes.

Are both your leak gauge and compression gauge the screw-in-the-sparkplug-hole type?

Cranking compression is somewhat dependent on battery charge temperature of the starter and more. Keep everything constant, particularly the number of compression strokes measured.

If another round of tests shows similar results our first question is going to be “Where is the leak?”

Almost regardless, we will send you out for more spirited driving. IF there is a problem you want to know exactly what and where. Consider disassembling your engine and NOT finding any obvious malfunction. “Now what?”

It may very well turn out nothing is wrong but a little smoke. Geriatrics is frustrating.

Best,
Grady

Thanks Grady! I appreciate your well-constructed advice. I can certainly use this information for a second round of tests.

Cheers,
Craig