How to do a proper compression test!?

[wlbolerdo]

I have rebuilt my '92 70hp evinrude and have put about 5 hours on the motor. A mechanic told me that the compression was 140psi. I thought this was high. I did my own and had 100psi on all three, exactly!
I removed one plug at a time and checked each cylinder as opposed to pulling out all three at one time and checking them.
What's the proper procedure? The powerhead has been bored to 30 over and all parts are evinrude, not aftermarket.
Wayne

 

[James R]

Re: How to do a proper compression test!?

The compression testers vary all over the place so acurate readings are difficult to obtain. Pull all the plugs leave the ignition off and jumper across the starter solenoid. Alternatively provide a ground for all the plugs so that they hang away from the plug holes and use the switch to crank the motor.This is to avoid overloading the CD unit.
For best figures you need to have the throttle open.
The main thing is to have even compressions or close to. I have just done a '91 70HP. I have 135PSI.

 

[HighTrim]

Re: How to do a proper compression test!?

As stated, dont sweat the figures, just the difference. You're numbers are great.

No need to advance the throttle either.

 

[wlbolerdo]

Re: How to do a proper compression test!?

Thanks for the info. I wanted to see it for myself for future reference. Does the compression increase after the rings have wore in?
Wayne

 

[kenmyfam]

Re: How to do a proper compression test!?

Different compression testers give different results. The difference is the key. Seems as though you have no issues with yours.