360 Cylinder P.S.I.

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69wacuda

69wacuda

Handling, and a 500ci engine.... All in good time!
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What should my cylinder compression (psi) be on my 360? I was told that the engine doesn't have very many miles but I have check three of the cylinders and they read 83, 75, 78 p.s.i. so far. I thought compression should be in the low 100s? Thanks.
 
reading should be over 100 PSI in each cylinder and no more then a 20% difference between them all. How long has it been since its been running? could be the cylinder walls are dry, did you try putting a tiny bit of oil in each and retesting? whats the oil pressure?
 
Those numbers are low. How did you do the test, cold, warm? Wet, dry? All plugs out and carb open?
 
Yes..
How was the test done?
Was the engine warmed up first or cold?
What mods have been done to the engine?
 
Those numbers are low. Try putting a couple of squirts of oil in the cylinders and repeat the test. If the results improve you are leaking in the ring/piston area. If they do not go up, your problem is in the heads/valves.
 
krazykuda said:
Those numbers are low. Try putting a couple of squirts of oil in the cylinders and repeat the test. If the results improve you are leaking in the ring/piston area. If they do not go up, your problem is in the heads/valves.
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also it could indicate the engine hasen't been running in along time if there low and you haven't heard the engine running, never start an engine that has been sitting without priming the oil pump and putting a little lubercation on the rings via a squirt of oil down the plug hole
 
the test was done cold with all the plugs out. The car had been sitting for over 24hrs when I did the test. Also the car has been driving and running great for the last 6 months, up until a week ago. it started to idle exceptionally rough and at cruising speed would have an intermittent hesitation that didn't happen under acceleration. I will squirt a little oil down the hole and check all of them and return with the numbers.
 
I have 120psi on all mine, goes over 150 if squirt oil in cylinders beforehand. If all cylinders are low - how about a severely stretched timing chain?? Anyone. I know if you
put the timing chain in advanced it will increase compression some.

Think you can pull off the distibutor cap and manually crank motor back and forth to check for that.(Just throwing something out there)
 
so i tested all of the cylinders with a little bit of oil in them, and 7 of them are with in a range from 83-90 psi. and one ( 2nd from the front, passenger side) is at 100. the car was running really well up until a week ago. what does this mean for me?
 
i should also note that when i noticed it running roughly, i removed the spark plug wire from the number 1 cylinder (while it was running) there was no noticeable change to how it was running at idle. the spark plug looked like it was good and seemingly only failed to fire at low rpm or idle. i have a new distributor and plug wires. How can i check either of these components?
 
If you are getting low compression the quickest way to tell what the problem is would be to do a leak down test. It will tell you way more than a compression test ever will. Pressurize the cylinder with air while the valves are supposed to be closed and look for the air leak, Out the carb - intake valve not sealing. out the exhaust - exhaust valve not sealing. out the dipstick- rings. out the radiator or the next cylinder- head gasket.
 
Fire it up, let it get to operating temp. Then pull all the plugs, block the carb wide open, and test it again. First, without oil, then with. It sounds more like it's just got ignition issues that could be caused by ignition parts or carb being off. I'll bet if you get it to operating temp the numbers will climb to over 115.
 
well you did say the engine has low mileage you were told. but i have seen timing chains jump a tooth(or 2) from having many miles on them and the compression took a dump. the ignition timing took a dump too from the slipping chain. i set the timing up and nursed the car home. checked the compression and it was all around 90 lbs replaced the chain and it ran like a top. this is probably not your problem but its what happen to me so i threw it out there.
 
Sounds like a wore out pos.
 
moper said:
Fire it up, let it get to operating temp. Then pull all the plugs, block the carb wide open, and test it again. First, without oil, then with. It sounds more like it's just got ignition issues that could be caused by ignition parts or carb being off. I'll bet if you get it to operating temp the numbers will climb to over 115.
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THIS, you have to do the compression test the proper way before you know fer sure.
 
Sounds like it got the cam knocked out of it.... Check for the cam going flat...
 
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