compression test
Thread Starter
Pro
Joined: Jun 2007
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From: Quebec, Canada
compression test
When performing a compression test, for how long do I crank the engine? For example, is there a fixed number of revolutions or do I just keep cranking until the pressure no longer increases?
Race Director
Joined: Feb 2007
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From: northern california
C2 of Year Finalist (track prepared) 2019
I crank until the pressure stops increasing. Generally that takes five compression cycles +/-
Last edited by jim lockwood; Apr 18, 2024 at 10:31 AM.
Drifting
Joined: Oct 1999
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From: Corrales NM
I count to seven revolutions for each cylinder. To get a apples to apples comparison between each cylinder I felt it important to rotate each cylinder the same number of times. This logic may be totally flawed. I am not an expert on compression testing.
Burning Brakes
Joined: Apr 2020
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One time I did the test and after it was completed I started the car and drove off. Got to where I was going, shut it down and 20 minutes later returned to a dead battery.
Fair warning!
Eddie
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From: northern california
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Just make certain to have a battery charger on hand when you do this, It is very easy to get involved and that battery runs down really fast. When you are finished with the test I recommend that you put the charger on for a bit to straighten it all out.
One time I did the test and after it was completed I started the car and drove off. Got to where I was going, shut it down and 20 minutes later returned to a dead battery.
Fair warning!
Eddie
One time I did the test and after it was completed I started the car and drove off. Got to where I was going, shut it down and 20 minutes later returned to a dead battery.
Fair warning!
Eddie
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Burning Brakes
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I thought of that but upon testing and monitoring, it seems as though all is in order. I see a steady 13.5 to 14.4 volts all during my drives, day or night. I suspect that the battery is not as substantial as I might think and further----I might have gotten a "Little aggressive" by over cranking during the test(s).
I was trouble shooting my rebuild(excessive oil consumption) and might have become too focused on things.
More on this in another post to come.
Eddie
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Joined: Sep 2008
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Jim,
I thought of that but upon testing and monitoring, it seems as though all is in order. I see a steady 13.5 to 14.4 volts all during my drives, day or night. I suspect that the battery is not as substantial as I might think and further----I might have gotten a "Little aggressive" by over cranking during the test(s).
I was trouble shooting my rebuild(excessive oil consumption) and might have become too focused on things.
More on this in another post to come.
Eddie
I thought of that but upon testing and monitoring, it seems as though all is in order. I see a steady 13.5 to 14.4 volts all during my drives, day or night. I suspect that the battery is not as substantial as I might think and further----I might have gotten a "Little aggressive" by over cranking during the test(s).
I was trouble shooting my rebuild(excessive oil consumption) and might have become too focused on things.
More on this in another post to come.
Eddie
Burning Brakes
Joined: Apr 2020
Posts: 962
Likes: 357
I agree with you but does it not also depend on how long and often one cranks the engine. Especially if the one doing the compression test is a novice at the test and tends to over crank also, just doing the test in many cases indicates a problem which means the tester is concerned about a potentially serious problem and in that frame of mind might do a lot more cranking than a more experienced person.
I only made that suggestion as a caveat. It cots nothing to have a charger on hand "just in case."
And yes, one time when I got burned by this it was dues to a bad battery.
Eddie
Drifting
Joined: May 2023
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From: Sierra Vista, AZ
The charging system doesn't like when the battery gets run down, it's a good idea to charge it after extended cranking, before using the car. Then again, a tired battery will not be able to crank the engine as long as a fresh new battery will.
So you're both right
So you're both right
Burning Brakes
Joined: Apr 2020
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Thanks for simplifying.
Eddie