Compression Test Procedure?
Thread Starter
Drifting
Joined: May 2000
Posts: 1,478
Likes: 38
From: Long Island NY
Compression Test Procedure?
Not sure about the proper method of a typical compression test. First, disconnect coil, block carb open and then....must all plugs be removed prior to the beginning of the test, or must one cylinder at a time be tested while the plugs remain in the other cylinders? Also, does the depth of the threaded hose for the tester affect the compression readings. In other words would a longer threaded fitting cause a higher compression reading? Any info would help. Thanks, L8TER, Paul.
[Modified by Vettesic, 4:22 PM 4/29/2002]
[Modified by Vettesic, 4:22 PM 4/29/2002]
Melting Slicks
Joined: Jul 1999
Posts: 3,201
Likes: 0
From: Clifton Park NY
Re: Compression Test Procedure? (Vettesic)
I haven't done the test yet, but the service manual says all plugs must be removed, while the instructions that came with the tester say all plugs must be loosened.
-Pedro
-Pedro
Melting Slicks
Joined: Feb 2001
Posts: 3,330
Likes: 13
From: Europe , Luxembourg
Re: Compression Test Procedure? (Vettesic)
Hi
Yes, remove all plugs, this will free the force to turn the engine by the starter motor. Otherwise it has to compress the air.
Also disconnect the power lead to the ignition coil to eliminate it sparking all over the place.
Don't worry about the carb, just don't touch the pedal.
Now you can turn the engine with the starter about two compression strokes per cylinder tested.
The lenght of the fitting used does not change the reading, at least not noticeable. Anyway, your looking for equal reading between all cylinders, not realy for a high PSI value !
Good luck.
Gunther :seeya
[Modified by WESCH, 4:25 PM 4/29/2002]
[Modified by WESCH, 4:26 PM 4/29/2002]
Yes, remove all plugs, this will free the force to turn the engine by the starter motor. Otherwise it has to compress the air.
Also disconnect the power lead to the ignition coil to eliminate it sparking all over the place.
Don't worry about the carb, just don't touch the pedal.
Now you can turn the engine with the starter about two compression strokes per cylinder tested.
The lenght of the fitting used does not change the reading, at least not noticeable. Anyway, your looking for equal reading between all cylinders, not realy for a high PSI value !
Good luck.
Gunther :seeya
[Modified by WESCH, 4:25 PM 4/29/2002]
[Modified by WESCH, 4:26 PM 4/29/2002]
Drifting
Joined: Oct 2000
Posts: 1,825
Likes: 56
From: Shawano WI
Re: Compression Test Procedure? (Vettesic)
Anytime that I did a compression test I always remove all the plugs so the motor will spin over easier. Otherwise the starter has to fight the compression of the other cylinders and it runs the battery down quicker.
The depth of the hose ftting will not alter the compression reading but make sure it is not too long as to hit the piston.
The depth of the hose ftting will not alter the compression reading but make sure it is not too long as to hit the piston.
Pro
Joined: Jan 2000
Posts: 569
Likes: 0
From: SLC, UT USA
Re: Compression Test Procedure? (Vettesic)
Somewhere I heard about squirting oil in the cylinder if it has low pressure, and if the compression comes up this indicates either worn rings or valves or something. Anyone know anything about this test procedure?
Team Owner
Joined: Feb 2001
Posts: 49,198
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From: All in!
Cruise-In IV Veteran
St. Jude Donor '03-'10
Re: Compression Test Procedure? (dsagers)
Somewhere I heard about squirting oil in the cylinder if it has low pressure, and if the compression comes up this indicates either worn rings or valves or something. Anyone know anything about this test procedure?
If it stays the same you probably have a valve seal problem.
Thread Starter
Drifting
Joined: May 2000
Posts: 1,478
Likes: 38
From: Long Island NY
Re: Compression Test Procedure? (Chris Fowler '80)
OK Guys, Yes I know about the oil the cylinders. Thanks all for the lesson in compression testing. Wasn't quit sure. I haven't done one in a while, so I just needed a little brushing up. I can always count on the CF members for the right answers!! :yesnod: L8TER, Paul.
Melting Slicks
Joined: Dec 2000
Posts: 3,407
Likes: 2
From: Carmichael CA
Re: Compression Test Procedure? (Vettesic)
OK, I've done my compression tests before like the others...by removing all the plugs, and testing by cranking the engine over. However, after draining the battery and overheating the starter on one of my fleet vehicles I decided to keep all the plugs in except for the one I'm testing, and actually start the car (keep the coil and everything intact). The engine spins a bit faster and provides a much better reading that one obtained by cranking with the starter.
Also, it won't matter how deep the tester goes...the pressure will be the same no matter where in the chamber you test. Personally, I like the ones that have a rubber tip and you just press and hold it where the plug goes...that way I don't have to take the time to screw the tester in each hole...I just remove the plug, hold the tester in place, start the car for about a second, then turn it off, remove the tester, and replace the plug and wire.
In any case you should get a remote ignition switch so you can crank/start the engine while at the front of the car in the engine compartment.
Also, it won't matter how deep the tester goes...the pressure will be the same no matter where in the chamber you test. Personally, I like the ones that have a rubber tip and you just press and hold it where the plug goes...that way I don't have to take the time to screw the tester in each hole...I just remove the plug, hold the tester in place, start the car for about a second, then turn it off, remove the tester, and replace the plug and wire.
In any case you should get a remote ignition switch so you can crank/start the engine while at the front of the car in the engine compartment.
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Le Mans Master
Joined: Apr 2002
Posts: 7,281
Likes: 5
From: Boston
Re: Compression Test Procedure? (Rockn-Roll)
OK, I've done my compression tests before like the others...by removing all the plugs, and testing by cranking the engine over. However, after draining the battery and overheating the starter on one of my fleet vehicles I decided to keep all the plugs in except for the one I'm testing, and actually start the car (keep the coil and everything intact). The engine spins a bit faster and provides a much better reading that one obtained by cranking with the starter.
Also, it won't matter how deep the tester goes...the pressure will be the same no matter where in the chamber you test. Personally, I like the ones that have a rubber tip and you just press and hold it where the plug goes...that way I don't have to take the time to screw the tester in each hole...I just remove the plug, hold the tester in place, start the car for about a second, then turn it off, remove the tester, and replace the plug and wire.
In any case you should get a remote ignition switch so you can crank/start the engine while at the front of the car in the engine compartment.
Also, it won't matter how deep the tester goes...the pressure will be the same no matter where in the chamber you test. Personally, I like the ones that have a rubber tip and you just press and hold it where the plug goes...that way I don't have to take the time to screw the tester in each hole...I just remove the plug, hold the tester in place, start the car for about a second, then turn it off, remove the tester, and replace the plug and wire.
In any case you should get a remote ignition switch so you can crank/start the engine while at the front of the car in the engine compartment.
Paul
Thread Starter
Drifting
Joined: May 2000
Posts: 1,478
Likes: 38
From: Long Island NY
Re: Compression Test Procedure? (inferno-vette)
OK, I get it. However, I'm only a back-yard mechanic. Working in the crammped quarters of a Vette's engine bay....one would get a lotta burns from the hot manifolds by the time you get to # 8 cylinder. :eek:
