high compression in one cylinder?
Thread Starter
Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
high compression in one cylinder?
it's a 5.7 with unknown history. i drove the car before i started the frame off, and it seemed to run ok, but now i have the engine out and i ran a compression check. i get 150 psi on all except #4 which is 180 psi. all readings are cold engine. the plugs all looked clean. the heads are 3973487X.
any thoughts?
any thoughts?
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Check it again a couple of time, somting wong, sounds like you have a normally worn in ( I didn't say worn out ) motor with the 7 cylinders all the same whatever the pressure might be.
Kinda odd to have one 30psi higher, now one 30 psi lower is more of a common occurrence, check again a couple more times, then squirt oil in all of them and check again and see what you get. Warm it up first, possibly a valve is sticking closed too long or not even opening at all giving a higher reading on that cylinder.
How does it run ? Usually when someone does this test they are trying to fix a problem
Kinda odd to have one 30psi higher, now one 30 psi lower is more of a common occurrence, check again a couple more times, then squirt oil in all of them and check again and see what you get. Warm it up first, possibly a valve is sticking closed too long or not even opening at all giving a higher reading on that cylinder.
How does it run ? Usually when someone does this test they are trying to fix a problem
Melting Slicks
Joined: Sep 2004
Posts: 2,655
Likes: 19
Cold engines are not much good for compression checks. Make sure there's no coolant in the cylinder, start it up, rerun the compression check. It only take a few minutes of running to stabilize the readings, but a warm engine is ideal.
Instructor
Joined: Sep 2006
Posts: 175
Likes: 11
From: Omaha ne
THe only way to do a good check is with it warm and the throttle opened. Might be a lifter that is not pumped up. or possibly a worn cam lobe starting to rear it's ugly head. I would like to suggest that you forget about the issue until you can get the engine up to operating temp, pull all the plugs, open the throttle and repeat the test. Unless of course you're looking for a reason to rebuild the motor while it's out 
Burning Brakes
Joined: Jul 2008
Posts: 923
Likes: 37
From: Green Bay Wisconsin
Check compression on warm engine only. Cold engine readings mean nothing.
Douglas in Green Bay
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
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Thread Starter
Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
thanks for the info.
i pulled the engine because the frame on the car is severely rusted, it's actually cracked on the left kick-up, and i'm switching frames. as i stated, it seemed to run well in a test drive, but i wanted a little more information on the engine before i dropped the body. i don't want to spend the money on a rebuild right now, but i would be a lot easier now than later.
i pulled the engine because the frame on the car is severely rusted, it's actually cracked on the left kick-up, and i'm switching frames. as i stated, it seemed to run well in a test drive, but i wanted a little more information on the engine before i dropped the body. i don't want to spend the money on a rebuild right now, but i would be a lot easier now than later.
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
If you're worried about it, you can just use a cheap rering kit, cast rings, new crank and rod bearings, seals, gaskets and just deglaze the cylinder walls. Can do it with the engine still in the frame too. Heads can be done accordingly at a later date in the car.
Probably for less than 200 bucks. Hardest part is stopping at that.
Can last quite a while, until you get your ducks in a row.
Having the latest and greatest isn't always in the cards.
Probably for less than 200 bucks. Hardest part is stopping at that.
Can last quite a while, until you get your ducks in a row.
Having the latest and greatest isn't always in the cards.
