Y block cylinder compression
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New User
Joined: Jul 2016
Posts: 12
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From: Townsend, Ma
Y block cylinder compression
Ran the compression test, motor warm, all plugs removed and throttle wide open. These were the results.
1. 150psi
2. 150 psi
3. 130psi
4. 140psi
5. 125psi
6. 125 psi
7. 110psi
8. 135psi
Is this a normal range for the motor even with 7 being at 110? Can I assume the rings are good?
1. 150psi
2. 150 psi
3. 130psi
4. 140psi
5. 125psi
6. 125 psi
7. 110psi
8. 135psi
Is this a normal range for the motor even with 7 being at 110? Can I assume the rings are good?
Post Fiend
Joined: Feb 2008
Posts: 5,831
Likes: 121
From: St Albert, Alberta
Ran the compression test, motor warm, all plugs removed and throttle wide open. These were the results.
1. 150psi
2. 150 psi
3. 130psi
4. 140psi
5. 125psi
6. 125 psi
7. 110psi
8. 135psi
Is this a normal range for the motor even with 7 being at 110? Can I assume the rings are good?
1. 150psi
2. 150 psi
3. 130psi
4. 140psi
5. 125psi
6. 125 psi
7. 110psi
8. 135psi
Is this a normal range for the motor even with 7 being at 110? Can I assume the rings are good?
General rule of thumb is no more than a 10% variation between highest and lowest cylinder.
I would do a wet test next to check the rings. Add a teaspoon of oil to each cylinder and retest. If the readings jump then you have worn rings. If not then think valve problems.
Post Fiend
Joined: Jun 2003
Posts: 8,209
Likes: 12
From: Black Hills of SD
Having been in the auto repair business and a hobbiest most of my life, that actually is pretty common in older carburated engines. While not ideal numbers, I probably wouldn't freak out and rebuilt it as long as none were under 100. However if it does prove to be a valve with the wet test, it might be a good time to pull the heads and do hard seats.
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