Compression test today, rebulid?
Thread Starter
Pro
Joined: Nov 2009
Posts: 583
Likes: 0
From: Maple Grove Minnesota
Compression test today, rebulid?
I did a compression test today here are the results. 1989 with 178,000 miles.
Cylinder 1 = 150, 2 = 180, 3 = 120, 4 = 145, 5 = 120, 6 = could not get at, 7 = 150, 8 = 150
Do these results constitute a rebuild or maybe problems with the heads?
Cylinder 1 = 150, 2 = 180, 3 = 120, 4 = 145, 5 = 120, 6 = could not get at, 7 = 150, 8 = 150
Do these results constitute a rebuild or maybe problems with the heads?
Le Mans Master
Joined: Feb 2005
Posts: 6,485
Likes: 566
From: Clearwater Florida
.......... If its running OK and not smoking or doing anything embarrassing ... drive the s**t out of it and start saving your pennies and nickles so you can build a motor that'll put a big smile on your face ... 
...
...
Melting Slicks
Joined: Aug 2003
Posts: 3,403
Likes: 398
From: Lakeville MI
I just ran a compression test on my (recently broken) 98,000 mile 88.
Here are my results for comparison:
1. 160 psi
2. 175 psi
3. 90 psi
4. 155 psi
5. 160 psi
6. 150 psi
7. 165 psi
8. 150 psi
I'm thinking my #3 piston is cracked.
Considering your #3 and #5 cylinders are both low at 120 psi, you may have a head gasket leak between them. All other values appear to be within reason.
Here are my results for comparison:
1. 160 psi
2. 175 psi
3. 90 psi
4. 155 psi
5. 160 psi
6. 150 psi
7. 165 psi
8. 150 psi
I'm thinking my #3 piston is cracked.
Considering your #3 and #5 cylinders are both low at 120 psi, you may have a head gasket leak between them. All other values appear to be within reason.
Thread Starter
Pro
Joined: Nov 2009
Posts: 583
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From: Maple Grove Minnesota
I’m not exactly sure how I’m going to approach this. I purchased everything I need to put an HSR on this motor.
I guess I could go one step further and pull the heads and replace the gaskets which I was considering anyway but then I might as well get a valve job at the same time. It does not burn oil and doesn’t smoke either even on start up.
Then on the other hand a local has a 400 it is a 72 four bolt main with a comp cam kit, not sure what else he has put into it other then fresh heads and it’s supposed to have 1500 miles on the build. He’s only asking $1300 for it and I could probably get it for less minus the 750 Holley and intake which I don’t need. Only problem is you don’t know what your getting.
I guess I could go one step further and pull the heads and replace the gaskets which I was considering anyway but then I might as well get a valve job at the same time. It does not burn oil and doesn’t smoke either even on start up.
Then on the other hand a local has a 400 it is a 72 four bolt main with a comp cam kit, not sure what else he has put into it other then fresh heads and it’s supposed to have 1500 miles on the build. He’s only asking $1300 for it and I could probably get it for less minus the 750 Holley and intake which I don’t need. Only problem is you don’t know what your getting.
Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
It is difficult if not impossible to get good compression reading on a hydraulic cammed engine. The lifters will bleed down with valve spring pressure and give you very high readings on the cylinders that bleed down. At the very least they will be very inconsistent. The compression tester can be used to check for major damage but it is hard to use it to determine overall engine health.
If the car runs well and does not burn oil your engine cylinder seal is probably OK.
If the car runs well and does not burn oil your engine cylinder seal is probably OK.
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Le Mans Master
Joined: Jan 2003
Posts: 5,858
Likes: 7
From: Santa Maria CA
You have a 30% difference from lowest to highest which is about double than what you should have max across the board. And your adjacent #3 and #5 cylinders look suspicious. I would run a liquid dye block test to check for a blown head gasket. It will tell you if any part of the head gasket that seals against the cooling system is blown.
Also do a "Wet" compression test now. Add about a tablespoon of motor oil using an oiler to each cylinder and retest. If you see a considerable increase it's an indication of lower end leakage past rings. If the change is miminal and numbers remain about the same it indicates a top end problem which means either the head gasket or valves or both.
If you run a liquid dye block test and it comes back negative and a wet test changes the readings little then you've pretty much narrowed it down to leaking valves in the head.
Last edited by 86PACER; Nov 29, 2010 at 11:32 PM.
