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Can someone please tell me how to correctly check compression? Do you warm up the motor first, then check? Throttle wide open? Five pulls. Help need some help don't want to tear into till I get this figured out. Thanks guys for all your help?

The squish is .07800
:blahblah: SWRules
 

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Egine warmed up,throttle wide open,and the engine only has to turn enough to put that clyinder through 1 compression stroke so at least 3 revolutions,5 revoloutions is the right number for a 4 stroke motor.
 

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I agree with everythng John said except you need about three to four comp. strokes to get the highest reading. Make sure the gauge is a good quality and its seated properly don't want to tear down a motor because of a faulty LOW reading :thumbsup:
 

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When the motor is brand new it makes 150psi when its pulled over cold. So why should you do it with the motor warm.

I would Keep the engine cold. Put the gauge in. Hold throttle wide open. And pull 4 times hard on the cord.
 

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MACHZZZZ 1, you are absolutley correct. If you check the compression with a warm engine you cannot get a consistent reading because the temp will be different every time which will change the reading. Engine cold, throttle open, 5 pulls, also 800 ski if you think you might have a problem a leak down test will find the smallest of problems, good luck, hope you dont have to tear it down.
 

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I agree with the the engine cold theory. When you check it cold, it's cold. When you check it hot, just how hot is it? Did you just turn it off or did it set for awhile? Did it idle to temp or did you go rip a couple of 1000 footers? Well...you get the idea. Consistency is what you want and you are closer to that when cold.
 

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A compression test should be done with a engine at normal operating temp. Piston(s) and cly(s) will be at actual running clearences, should give more of a accurate reading.
 

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Yeah but the factory designes the engine to make 150psi cold. So when checking you have to check cold. If you get 140 warm or 160 warm it doesnt matter as long as you get 150 cold.
 

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Machzzzz1, in what Bombardier repair manual doo you get these spec,s and proceedure? or any other repair manual for that matter?
 

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If you do a compression test on a new motor you will get 150 cold. That is what bombardier has in there manuals as stock spec.

So why do a check at anything but. If the engine is cold, its cold. But a warm engine can be very diffrent even from cylinder to cylinder.
 

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The number of revolutions,temp,and how hard you pull will vary every time you do a comp test, it should be up to temp,esspecially forged pistons,and the max comp is only a guide and will vary greatlly with your tool(in our shop you may see 3 diff readings with three diff gauge sets) the main thing is that there is no more than a 10 percent diff between highest and lowest that is where problems will be found.And also a leak down test is the most acurate>
 

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You got that right John I don.t even bother with a comp. test on a 2-stroke. A leak down down test is the must acurate way to deturmin a engines condition. Also done with engine at normal operating temp.
 
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