compression
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Low compression vs. high compression will affect the cylinder pressure numbers you get, but that's not important. What's important is that all cylinders be in the same range of pressure.
If you read all eight, and they are 120 high to 110 low, with some in the middle, your engine is ok. Maybe a bit worn but ok.
A higher range of numbers would be better.
What did you find with the other cylinders?
If you read all eight, and they are 120 high to 110 low, with some in the middle, your engine is ok. Maybe a bit worn but ok.
A higher range of numbers would be better.
What did you find with the other cylinders?
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Junior User
Joined: Sep 2009
Posts: 59
Likes: 0
From: ca
okay,here is what made me check my compression i just installed new headers,intake manifold and a carburetor,after running the engine for a while i noticed that 6 of the exhaust from the headers were burning good and 2 of them were hot but not as hot as the other 6 cylinders,also when when i press the gas pedal to the floor it sometimes back fires,some people tell me it's a sticky valve and other people tell me it's the carburetor,it didn't back fire before the swap,oh the compression was between 114-118.help please
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Joined: Apr 2004
Posts: 34,503
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If all cylinders are in that range, it's not a compression issue, and probably not a sticking valve. Do you ever hear tapping from the engine?
How are your ignition components? Points? Cap, rotor, wires in good condition? A cross-fire will give you a nice backfire.
Timing? Have you fooled with that?
Is your vacuum advance hooked up correctly?
How do the plugs look? Lean/rich conditions?
Have you checked your manifold to head seal? Since the manifold seal is under the valve cover, look for oil fouling on those cooler cylinders. A vacuum leak there is going to suck some oil from under the valve cover.
Did you check the condition of the timing chain/sprokets? With the distributor cap off, rotate the engine until you see the rotor move. Then reverse the rotation of the engine. (easier with the plugs out, you might still need a wrench on the crank) See how many degrees of crank rotation you get before the rotor moves. That's how much your timing can wander. You don't want much of that.
How are your ignition components? Points? Cap, rotor, wires in good condition? A cross-fire will give you a nice backfire.
Timing? Have you fooled with that?
Is your vacuum advance hooked up correctly?
How do the plugs look? Lean/rich conditions?
Have you checked your manifold to head seal? Since the manifold seal is under the valve cover, look for oil fouling on those cooler cylinders. A vacuum leak there is going to suck some oil from under the valve cover.
Did you check the condition of the timing chain/sprokets? With the distributor cap off, rotate the engine until you see the rotor move. Then reverse the rotation of the engine. (easier with the plugs out, you might still need a wrench on the crank) See how many degrees of crank rotation you get before the rotor moves. That's how much your timing can wander. You don't want much of that.
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