How to properly use a compression tester

[Boondockin800]

Ok guys don't laugh... but yes I'm serious about the topic. I know how to use a compression tester, but I'm curious about how many times to pull the engine over, how fast, etc. I noticed that I can get 150psi out of my 96 670 with 7 something thousand miles if I crank the hell out of the pullrope . But I'm curious how to get the most accurate reading.
Thanks for the help!

 

[M7 man]

its should only be like 2-4 pulls as most sleds start with 2 pulls. If it takes like 10 pulls then you know its hurt.

 

[Squeal]

Make sure the throttle is wide open. Compression tester is more of a comparison. Pull both sides the same. Should be within one or two pounds same compression. Compare compression after rebuild or new to a few thousand miles. Most all Compression tester will read different.

 

[Wyoming T/A]

on any motor you should pull it over 10--TEN-- times with the throttle held wide open----a auto engine requires the same amount of cranking----if your up around 130 to 150 psi your good

 

[Backcountry]

Throttle wide open and pull until the needle stops moving upwards. Make sure your compression tester has a schrader valve in the tip that threads into the head. And also a good idea to make sure its 3/4" long that threads into the head. If its shorter you will get a lower reading.

I do not like the pull it X times. Is that hard pull, semi-hard pull, 14.338 pounds of force or 32.1119998 pounds of force to pull it over, is your pull cord 3.1233 feet long or 4.44435 long????? Too many variables....

 

[Snow Flake]

I check the compression on my two strokes with the engine cold. Crank until the needle stops going up and write down the numbers to keep a trend record.

 

[diggerdown]

I check the compression on my two strokes with the engine cold. Crank until the needle stops going up and write down the numbers to keep a trend record.

Compression should be checked hot! Cold means nothing, I know of no one that rides or gets peformance from a cold engine.

 

[vmaxfrank]

I've always been told to check with the engine warm, not cold, not hot. I let it idle for 5 to 10 min. then crank with throttle until the needle maxs out. Main thing is cylinders are equal.

 

[Snow Flake]

Compression should be checked hot! Cold means nothing, I know of no one that rides or gets peformance from a cold engine.

Okay

 

[mattymac]

What ever you do, just make sure you do it the same way so that way all your readings are consistnat. Warmer engine temps and throttle opened will yeild higher compression readings. Also try to do them at the same elevation too!


I usually do a warm motor, throttle open pull hard till the gauge stops climbing, usually about 3-4 pulls.

 

[NoSecondChances]

Don't forget to ensure that the ignition switch is off and the kill switch is off as well before doing your compression test. Usually a decent motor will hit the high spot within 5 -6 pulls (from my experience anyway). Once the gauge stops moving, no need to pull more than that.

 

[Scott]

When you duct tape the throttle and test your compression with the throttle wide open....make sure the key is off and your tether is pulled out. LOL

 

[diggerdown]

I've always been told to check with the engine warm, not cold, not hot. I let it idle for 5 to 10 min. then crank with throttle until the needle maxs out. Main thing is cylinders are equal.

Ok, warm, not hot! Point is, compression does change from cold to warm. Last winter I checked a doo 800, 135 cold, 100 warm! Rings were rubber, you could almost tie them into a knot! When it was cold, oil seeping though the pump was pulled in and seal the rings. This is not that uncommon.

 

[Boondockin800]

Thanks for all the responses! I forgot to perform the test with the throttle open so I'll try again with the engine warm too.

 

[M7 man]

Compression should be checked hot! Cold means nothing, I know of no one that rides or gets peformance from a cold engine.

exactly a engine could lose compression the warmer it gets

 

[MJay]

I checked a couple sleds cold and warm last night. 05 F7 w/ 3800 miles was 140/138 cold and 135/130 warm. 06 M7 w/ 3600 miles was 145/145 cold and 142/142 warm. Pipe was off for all tests. Those numbers look good to me.

 

[A CAT]

And be shure you are using an altitude conversion chart for you're readings, EG, my built Olds 442 has a compression reading of 230 PSI at sea level but where I live now, 7,000 Ft. it is only 160 PSI. 10% cyl to cyl var. is ok