Check compression?

[chrislovessadie]

I want to go back and re-check the compression on my Mercury XR2 Black- max 150.
How is the best way to do that? I checked last weekend but after reading some post, I want to re-check to make sure I did it right. Thanks all!

 

[EBENZER]

Re: Check compression?

You can check the compression on a cold engine to get an idea but to get an accurate check you need a warm engine. First thing to do is run it maybe 10 minutes. Then remove all the plugs and ground them to block. Then screw in a good quality compression gauge and turn the motor over until the reading has maxed out ,usually 4 or more strokes, take the reading on each cylinder and compare them. You need a compression reading of at least 100 psi within 10% of each other. The xr2 can have different readings on each bank(side) so compare readings on the same bank. The xr2 ,from what i have learned,came from the factory with around 120 or so psi..so maybe that will give you an indication of the health of your engine.

 

[chrislovessadie]

Re: Check compression?

Thank you! when I tried it was cold, and I only pulled one plug at a time. Now that I know how I will see what I can get. Do you also know how to test the trigger? I don't know if the key should be turned to the "on" or do I have the boat running? I can poke into wire by flywheel, but do I need flywheel off for best readings?

 

[EBENZER]

Re: Check compression?

The triger as you know is located under the flywheel. This is what i would do..you need to remove the ,i think, 2 screws,that attaches the outer switch box to the inner switch box.Caution.. switch box must be grounded to block before cranking engine or damage will occur..ok..after you have detached switche boxes remove all trigger leads from switch box.
Then get you an ohmmeter and switch it to resistance x 100 and make for sure the leads are as follows.
between brown trigger lead(without yellow sleeve) and white trigger lead(with yellow lead) must be between 1100-1400 ohms
between white trigger lead(without yellow sleeve) and violet trigger lead (with yellow sleeve) must be 1100-1400 ohms
between violet trigger lead(without yellow sleeve) and brown trigger lead(with yellow sleeve) must be 1100-1400 ohms..
if all are within spec trigger is ok..