Proper compression testing. 3 questions.

bang4dabuck · Apr 22, 2010

1) 4 or 5 cranks VS crank until compression peaks ?

2) All spark plugs pulled VS all other plugs in but disconnected ?

3) A good squirt of CRC/PB Blaster in each cylinder for lubrication. Will it alter the results ?

ab1 · Apr 22, 2010

Re: Proper compression testing. 3 questions.

1. I generally find that 4-5 cranks will be the peak compression anyway. Just do the same for all cylinders
2. I disconnect and pull all plugs....of course, pull your kill switch too. Keep plugs in order so you can diagnose if needed and pay attention to wire locations.
3. I Never bother with any kind of lube...just run the motor beforehand until it gets to operating temp.

The top secret file has directions...I never bother with opening the throttle either.

Hope this helps!

Faztbullet · Apr 22, 2010

Re: Proper compression testing. 3 questions.

1) 4 or 5 cranks VS crank until compression peaks ?

2) All spark plugs pulled VS all other plugs in but disconnected ?

3) A good squirt of CRC/PB Blaster in each cylinder for lubrication. Will it alter the results ?

1) 4 or 5 cranks with throttle wide open
2) pulled and grounded
3) Yes

JB · Apr 22, 2010

Re: Proper compression testing. 3 questions.

Faztbullet said:
1) 4 or 5 cranks with throttle wide open
2) pulled and grounded
3) Yes

Sorry to disagree, bullet.

1) 4 or 5 cranks, exactly the same on all cylinders. Throttle position is irrelevant.

2) Pulled and ignition disabled.

3) Adding anything to the cylinders will cause false readings. Don't do it.

See the post in the Top Secret file.

torbjorn · Apr 22, 2010

Re: Proper compression testing. 3 questions.

bang4dabuck said:
1) 4 or 5 cranks VS crank until compression peaks ?

2) All spark plugs pulled VS all other plugs in but disconnected ?

3) A good squirt of CRC/PB Blaster in each cylinder for lubrication. Will it alter the results ?

DON'T add anything to the cylinders, you'll get a false high reading.

bassfearmee · Apr 22, 2010

Re: Proper compression testing. 3 questions.

Motor should be warmed up too.

glassmaster68 · Apr 22, 2010

Re: Proper compression testing. 3 questions.

Listen to the red sky at night lover.JB

Faztbullet · Apr 24, 2010

Re: Proper compression testing. 3 questions.

Found the OMC service notes from school in Morrow,GA on how to perform compression check.
1) Engine warm if possible, theory is this ensures cylinders are wetted down from fuel mixture
2) Plug wires removed from plugs
3) Plugs installed !,this keeps bendix from jumping out of flywheel when cranking on V engines
4) Throttle handle at WOT
5) Key in off position and watch feet as prop will turn when testing, this is using a starter button on the solenoid

JB · Apr 24, 2010

Re: Proper compression testing. 3 questions.

Well, there are several points on which I disagree with the OMC Instructor. Too bad because I probably trained him.

samo_ott · Apr 25, 2010

Re: Proper compression testing. 3 questions.

JB said:
Well, there are several points on which I disagree with the OMC Instructor. Too bad because I probably trained him.

Those instructions do seem odd! Huh. So it's your fault JB for training him that way?

JB · Apr 25, 2010

Re: Proper compression testing. 3 questions.

No. I need to keep track of time. I stopped training OMC Instructors about 1980.

I taught them how to teach rather than what to teach, anyway.

I have a perfect memory, I just forget the password now and then.

Proper compression testing. 3 questions.

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