Checking Engine Compression

[Orange]

I was wondering if anyone has a step-by-step tutorial (with pictures?) on how to use a compression gage. From reading the posts here, it seems like you insert the gauge where the spark plug goes and turn the engine. I don't know how to turn the engine without turning it on, and I'm sure there are a few steps I missed.

I have a 1998 Seadoo speedster that was checked before I bought it, but now I'm looking at a PWC and want to check it out myself.

Thanks

 

[Nate Surveyor]

Here is a sort of step by step.

Remove spark plug wires, and re hook them to the provided posts, that ground them out.
Remove the spark plugs.
insert the compression tester, (screw it into the spark plug hole) on one cylinder) snug it up so it cannot leak air.
Hold the throttle wide open (WOT)
Crank it over for about 20 seconds, and when the compression tester reaches max, then that is the number for that cylinder.
Then repeat for all the cylinders.
all cylinders should be about the same. (less than 5 lbs difference)
If one is say 120 lbs, and all the others are 140, then that is bad. It would be like an Olympic runner, with a splinter in her foot. She won't do well. The motor is out of harmony. Like a race horse and a mule in a harness together. They wear each other out.
This is the basic method for compression checking marine motors. Compression checker is a great way to look at a motor's condition.

Hope this helps. :cheers:

Nate

 

[kustomkarl]

You'll need a compression tester. Go to Auto Zone. I think they sell for like $25.00. The compression gage, will screw in the cylinder head in place of the spark plugs. To test compression, remove both spark plugs. Place spark plug caps on the plug cap studs near the cylinder head to ground the empty caps. This completes the circuit of the ignition electrical system and prevents any electrical problems from the caps being un grounded. Using the correct adapter for the threaded end of the tester,( same length of the spark plug threads length)screw in the tester in one plug hole. Hold the throttle wide open. Push the start button. Watch the compression gauge, when it peaks out at the most compression, let go the start button. Read the psi number. I would do it 3 times to be sure it is accurate. Check both cylinders the same way. The ideal compression is 150 psi per cylinder. If it is less, it's not a problem as long as they are close to being the same. If the psi is less than 90 it might need be time for a tear down and a rebuild. If the psi in 1 cylinder is say 140 psi and the other is 80 psi you need to tear down and repair. This difference is a lot then there is a problem. I hope this helps you.

Karl

 

[Nate Surveyor]

I like Karl's better than mine.

Nate

 

[JamesC]

I am looking at buying a 96 Searayder and I would like to do a compression test on it. My question is what size are the spark plugs on these engine? is it the standard 5/8" spark plug with a 14mm thread like on most car engines or is it a different size plug I am a mechanic but I have very little boat experience. I tried to look at the manuals but I am not a premium member yet.

 

[seadoosnipe]

Seadoo's....

The F-14 Sea Rayder is not a Seadoo. It may look simalar but it's not. It has a Mercury, 120 HP engine in it. I have no idea what type plug is in it. Sorry.......:cheers: