Compression Test Question

TEEKIZZLE · Jul 10th, 2017, 13:01

Question with the procedure for the test. Do you keep cranking until it stops building or stop after a number of cranks? I was seeing consistent buildup after 3 cranks on all cylinder but on a few attempts noticed if I didn't cut it off after the 3rd it would build further.

Haynes states "after one or two revolutions, the compression pressure should build-up to a maximum figure, and then stabilize"... which is why I didn't want to crank past 3.

Didn't know the target values and wasn't sure if continuing to crank would cause any harm. After 3rd crank the values were 150-155psi.

Do the test again and let it max out or did I do the test properly?

/Cheers
TK

flyingtech55 · Jul 11th, 2017, 20:57

What I do is:

Remove all four spark plugs and if you can, disable/pull the fuse for the ignition system. Fit the gauge to the first cylinder. Crank the engine for probably five to ten seconds with throttle wide open. You will see the gauge rise rapidly then stabilise. Read off the pressure and write it down. Repeat for the remaining three cylinders.

You are generally not interested in the actual pressure provided it is in the region of 120 to 150 PSI (for petrol engines) but all four should be in the same ball park. If one cylinder is markedly different then that indicates a potential problem.

HTH

Tim

pookie · Jul 12th, 2017, 01:37

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Just like this.
If you want you can put a bit of oil down the bore and do a "wet" test.

Salut!

Pookie

Jul 10th, 2017, 13:01	#1
TEEKIZZLE Member Last Online: Apr 28th, 2024 18:23 Join Date: Jan 2014 Location: Doylestown	Compression Test Question Question with the procedure for the test. Do you keep cranking until it stops building or stop after a number of cranks? I was seeing consistent buildup after 3 cranks on all cylinder but on a few attempts noticed if I didn't cut it off after the 3rd it would build further. Haynes states "after one or two revolutions, the compression pressure should build-up to a maximum figure, and then stabilize"... which is why I didn't want to crank past 3. Didn't know the target values and wasn't sure if continuing to crank would cause any harm. After 3rd crank the values were 150-155psi. Do the test again and let it max out or did I do the test properly? /Cheers TK __________________ 03' S40 89' 740 GLE

Jul 11th, 2017, 20:57	#2
flyingtech55 Senior Member Last Online: Feb 18th, 2024 12:18 Join Date: May 2013 Location: Ayrshire	What I do is: Remove all four spark plugs and if you can, disable/pull the fuse for the ignition system. Fit the gauge to the first cylinder. Crank the engine for probably five to ten seconds with throttle wide open. You will see the gauge rise rapidly then stabilise. Read off the pressure and write it down. Repeat for the remaining three cylinders. You are generally not interested in the actual pressure provided it is in the region of 120 to 150 PSI (for petrol engines) but all four should be in the same ball park. If one cylinder is markedly different then that indicates a potential problem. HTH Tim Last edited by flyingtech55; Jul 11th, 2017 at 21:52. Reason: Information corrected

Jul 12th, 2017, 01:37	#3
pookie Premier Member Last Online: Apr 2nd, 2021 21:13 Join Date: May 2006 Location: Stockport	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Just like this. If you want you can put a bit of oil down the bore and do a "wet" test. Salut! Pookie __________________ Growing old disgracefully

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