Compression test question

[tony4pyro]

I am going to do a compression test on my 1986 Force 125HP, and I have read that you want to keep the spark plug wires grounded to avoid frying the electronics. My question is, can I just pull one plug at a time and simply keep the kill switch activated while I crank the engine, and, how would I ground the wires? (This may be a stupid question, but I have never run a compression test on anything before, and I DEFINITELY do not want to wreck anything.) Replies are always appreciated.

 

[gregmsr]

Re: Compression test question

Keep the kill switch activated. You will be fine.

 

[foodfisher]

Re: Compression test question

Don't use the key to turn it over and just jumper the solenoid/ or pull all plugs, put them back into the boots, and take a piece of bare wire, wrap each plug around the threads and fasten it to a bolt that is grounded to the motor. You need all plugs removed to free up the motor to spin fast enough to get a good reading. A good grounding bolt to use will have a black wire attached to it.

 

[Bifflefan]

Re: Compression test question

My question is, can I just pull one plug at a time

You should have all of them out to get a proper reading.

You can take the plug boots and just stuff them on a bolt head that they reach, this is fine to ground them.

 

[tony4pyro]

Re: Compression test question

If I don't use the key to turn the engine over, do I just spin the flywheel by hand?

 

[mmccoy555]

Re: Compression test question

The major reason you should ground out the wire is when you have the cylinders open and pumping it'll spit gas out of the cylinder. If those plug wires happen to ground out by accident and make spark your gonna be shaving facial hair you don't want to if not worse. You need to crank the engine over with power to get a proper reading. Just remove the wire you want to test and disconnect your coil packs from power. That way you know your not gettin spark running through those wires. Screw in your tester, turn the engine over a few times till the guage stops and get your reading. You can also leave the tester attached with pressure still through it for a couple minutes and see if it goes down at all. This will tell you if you have any other leaks. You have to do that with the other plugs in though so the pressure doesn't run out of another cylinder.

 

[foodfisher]

Re: Compression test question

At the starter solenoid jumper the red battery wire to the yellow wire. Be careful, the motor will spin.