| spqr67 | -- 10-27-2012 @ 1:19 PM |
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I'm a little afraid I know what the answer is but here goes....just did a compression test on the flattie our of my 50 Ford. As I thought, low compression on all cylinders (about 95 per) but no blow-by as far as I can tell. However, cyl #3 had NO compression. None. Being new to the hobby, I'm stumped. Thoughts on cause? Thanks Michael
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| alanwoodieman | -- 10-27-2012 @ 1:45 PM |
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stuck valve-squirt some marvel mystery oil in cylinder thru spark plug hole-you might even get extremly lucky and can see the stuck valve thru the spark plug hole, do the mmo for several days and if you can see the valve-tap it lightly with a wooden dowell/hammer-last resort pull the head
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| Old Henry | -- 10-27-2012 @ 1:50 PM |
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Listed from easier to fix to harder to fix these are some possibilities: 1. Valve stuck open. Possible broken valve spring, broken lifter, broken valve, or just stuck with cr*p. 2. Really bad piston rings although less likely. Any rings at all should create some compression. 3. Piston connecting rod broken and piston not even moving in cylinder. Way unlikely without some real racket in the crankcase but still a possibility. Those are my thoughts. Others might have others. P.S. Before tearing into anything do another test. Your test fixture may not have been tight in the sparkplug hole. P.P.S. I wouldn't consider 95 psi compression very low. Spec for new engine at sea level is only 105-125 lbs. and goes down with altitude. Your compression is as good as mine was right after my engine was rebuilt at 5,000 feet elevation. Old Henry (The older I get, the better old looks.)
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| supereal | -- 10-27-2012 @ 3:26 PM |
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If there was no racket, I'd suspect a stuck valve, broken valve spring, or the retaining fork than holds the valve assembly has come loose. You may be able to see the valve head thru the spark plug hole and determine if the valve is closing. It is likely that the intake manifold will have to come out. That isn't a big job, but will give you full access to the valve train.
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| spqr67 | -- 10-27-2012 @ 4:17 PM |
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Great advice all, thanks! Neglected to mention that #8 tested at 120 psi, much higher than the rest. Any cause for concern?
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| supereal | -- 10-27-2012 @ 8:45 PM |
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I'd retest it dry, then wet. With that much difference, a retest wil tell you if if it is correct. Better high than low, but that compression is high for even a newer engine.
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