| dggohl | -- 06-06-2015 @ 8:54 AM |
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I have a 239 flathead that has 0 compression. Other 7 are registering 75-80 psi. I removed head cover, turned the motor over. Valve is operating, piston is moving. Any suggestions?
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| shogun1940 | -- 06-06-2015 @ 9:00 AM |
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can you see the first ring down in side, if it there then bolt the head back on withthe valves closed and the piston at tdc. and put shop air in.. where it leaks out will tell you where the problem is. the old head gasket my leak a bit but it will give you an idea where to look
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| Stroker | -- 06-06-2015 @ 10:00 AM |
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Maybe there is a big "hole" in the top of the piston.
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| cliftford | -- 06-06-2015 @ 10:03 AM |
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If you still have the head off, inspect both valves and seats closely with the valves open. Look for rough spots or burns. If you have the head back on, do the air test as suggested, and listen for air coming out the exhaust pipe or intake manifold, which would indicate a leaking valve. If nothing, look for bubbles coming out the radiator filler, which suggest a leaking head gasket or [God forbid] a cracked block. Since only 1 cylinder is dead, you will probably find the problem this way.
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| dggohl | -- 06-06-2015 @ 2:09 PM |
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Thanks for the great info!
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| cliftford | -- 06-06-2015 @ 2:13 PM |
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Let me clarify my last post. I'm assuming that everything looked normal when you had the head off, no piston damage, no serious cylinder wall damage. If it were a leak into the cooling system, it be blowing coolant everywhere,given that this cylinder has 0 compresion. Also check the head. Admittedly,this on line diagnosing is at best educated guesswork. Let us know what you find. Good luck.
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| dggohl | -- 06-08-2015 @ 6:04 AM |
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Hi, I had the head on when I posted. So if I blow air into the cylinder, excuse my ignorance, but is there a special fitting to use that screws into the plug thread? Or, how else would I accomplish this? Thanks.
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| TomO | -- 06-08-2015 @ 6:34 AM |
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You can modify a spark plug or just fit a rubber end on your blow gun. It is important to have the piston at TDC on the compression stroke to ensure that the valves are closed. I would also put the car in gear, so the engine will not rotate. Tom
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| shogun1940 | -- 06-12-2015 @ 12:46 PM |
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if you can borrow the correct hose for a compession tester take out the valve in the end and you can use that hose. I would not put in gear, have the rotor in the distributor pointing at the spark plug wire in the distributor and watch if the engine turns one way or the other and then compensate by turning the engine alittle more or less so that the engine does not move when you put air in.. now your on tdc and you can determine where the air is coming out
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