460 compresion ?
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Junior User
Joined: Apr 2004
Posts: 53
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From: bassano alberta canada
460 compresion ?
i have a late 70s 460 moter it is sapose to be a donere moter for my mud boger.
did compresition test. it goes like this .
passengerside- from front to back is as follows.-150, 80, 100, 120.
drivers side- from front to back is as follows.-120, 80, 0, 120.
what couses this difrence. and can i fix this for cheep. funds have bin depleated on bilding bogger already.
the cylender that has 0psi. when doing test it would jump the needle up to 100psi then drope down to 0 psi. what would couse this? valves or ring?
any help would be gladly apretated. thank you.
did compresition test. it goes like this .
passengerside- from front to back is as follows.-150, 80, 100, 120.
drivers side- from front to back is as follows.-120, 80, 0, 120.
what couses this difrence. and can i fix this for cheep. funds have bin depleated on bilding bogger already.
the cylender that has 0psi. when doing test it would jump the needle up to 100psi then drope down to 0 psi. what would couse this? valves or ring?
any help would be gladly apretated. thank you.
Freshman User
Joined: Apr 2003
Posts: 34
Likes: 0
First did you have the throtle wired wide open when you did the test? This is standard proceedure for air to flow equally to the cylinders for the test.
Rule of thumb is if there is a 10% differential in any reading, the motor is faulty and sould under go a complete rebuild. The 0 reading tells me you have a bad valve on that cylinder.
Rule of thumb is if there is a 10% differential in any reading, the motor is faulty and sould under go a complete rebuild. The 0 reading tells me you have a bad valve on that cylinder.
Junior User
Joined: Dec 2004
Posts: 86
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From: Oak Harbor, WA
all the compession testers I have been using the needle stays at the highest reading. So you may have a faulty gauge or are using a very old gauge. If the gauge is accurate The low reading can be a couple of things but as WTAGAS said with the differential in the cylinders and the one cylinder reading zero that motor needs to be gone through.
Post Fiend
Joined: Sep 2004
Posts: 5,231
Likes: 1
From: Near Fresno, California
Normally you would put about a teaspoon of oil into the cylinders and rerun the test. If the pressure went up that would indicate bad rings. In your case it sure looks like you have burned valves - or a hole in the top of a piston.
The least you can do is to pull the heads and look to see what is going on. It is possible that a valve job will fix your problems - but, of course, a total rebuild would be better.
The least you can do is to pull the heads and look to see what is going on. It is possible that a valve job will fix your problems - but, of course, a total rebuild would be better.
