How to Compression Test a PWC

This video describes how to compression test a PWC and the condition of my SLT 750

[@buckwild6552]

Good to see a young man able to service his own equipment, most his age can’t put air in a bicycle tire.

[@michael3343]

Buckwild 65 here I am trying to study boat mechanics in school, my passion career and im 22.

[@iselili2]

I agree! Smart cookie his parents did a fine job raising him

[@kianroblin6413]

for real i’m 16 and half the kids my age don’t know how to do anything

[@nnickers3355]

Best vid on how to compression test. The top of the list hits skipped the small but important steps such as the kill switch. Nice work.

[@mattgehrke]

A compression tester is a must when purchasing a used jet ski 👍

[@gothamjetskier776]

Great work. Now that you're 5 years older I hope you're now building jet engines.

[@russg1801]

You're WRONG about the "added volume' of the hose - once you pump it up a few strokes it will reach the maximum pressure. Try it with a stubby gauge w/o the hose and you'll get the SAME number. Your cylinder is a pump!

[@aidansmith5726]

This was really helpful man, thanks.

[@jimmycox6235]

nice video young buck, very informative

[@iselili2]

Great video! Thanks for posting

[@nalakaabeysinghe9515]

Very good job. Explained very well.

[@micro1087]

Good video, very informative!

[@vikfan4life]

Thank you for sharing this!

[@oregon5034]

thanks for the video very helpful!

[@jamese498]

Good video very easy to understand.

[@basicwrench4510]

If you see the pressure decrease at all .. re -do the test with a teaspoon of oil in cylinder.. funnel through spark plug hole.. take not if you see the pressure decreasing.. If no - you have worn rings.. if yes- try another comp gauge or check o-reigns. - you should perform test with a warm engine .. or take note that a test done on a cold engine your pressure will be higher by a bit.. Hot air "cylinder " less dense.. Great video though.. post on on your new ski .. ( ;

[@ryanmcenroe8680]

Basic Wrench if the engine is hot and the air was less dense wouldn't the pressure be higher? For example, when your car tires are cool the pressure will be lower than once you have driven around a bit.

[@rf14dmb]

Ryan McEnroe that’s not how it works, you do it on a warm engine since an oiled cylinder is obviously how it runs and may increase compression slightly. A warm engine won’t falsely increase pressure like a tire. Also just FYI you are false about volume in the hose affecting pressure reading. It should be an air tight setup and the pressure in the cylinder equals the pressure in the hose which equals pressure at the gauge.

[@Stuntdriver44]

Great video!

[@seanmclean8054]

I own a 1996 slt 780 and is wonderfull

[@danielguzman8346]

Great video.. My mechanic checked my jetski and the engine compression was 120 on all of them. I have a 01 yamaha gp1200r jetski

[@TheTyphoon365]

Was thinking about buying a 1200 used, how's it treat you? the one I'm lookin at has been sitting for 5 years... but I hear they are pretty fast

[@nickmast45]

Hey have a quick question for any PWC knowledgeable people, am considering getting a close friends 2001 Yamaha xlt1200, engine was rebuilt 2 years ago by a trusted mechanic, taken out once to test. then stored in a garage for 2 years, occasionally started just to make sure battery was okay. Rolled it out of the garage for the first time in almost 2 years and turned it on, turned on almost instantly let it run for 5 minutes. Then compression tested it with a cheap gauge, all 3 cylinders showed 90psi, Im assuming it showed it that low because it was in incredibly cold start? All 3 were 90 so thats good, any thoughts?

[@ryanmcenroe8680]

Think about what creates pressure in a cylinder. When the piston pushes up in the second stage of a four stroke engine, it reduces the amount of space the matter inside takes up. This is to say it compresses it. The only possible way for the space to reduce but cause low pressure is if some of the matter inside has leaked out or the temperature is very low. The ideal gas law is represented as PV=nRT. You can actually do the calculation to find the difference in pressure based on the temperature. That being said, I wouldn't think it would cause the pressure difference you see. Check the manual for the ideal pressure per cylinder and if you're way off at least one variable in the ideal gas law. If you're trying to get high compression with a 6 foot long hose that will never happen. If your gauge is right in the cylinder and the temperature is good, you have a leak somewhere in the cylinder. It could be a bad seal between the piston and the cylinder or a gasket leak somewhere or a misalignment of the intake or exhaust valves. Give it some thought and do some research

[@rosel8140]

How'd you find which compression level it needed to be between? I'm going to check out a 95 sea doo bombadier spx and one sp and have to so this. good video

[@rosel8140]

do

[@ryanmcenroe8680]

sorry I am suburban exploration, I was using youtube as the wrong account

[@rysworld.]

👍

[@TheTyphoon365]

if I hold down stop, and try and turn it over (or remove the estop clip) I'm not able to turn it. But if I try and turn it normally it works...

[@ryanmcenroe8680]

I'm a little late replying but the idea is to stop the cylinders from firing. If you just unplug the spark plug caps and ground them it'll be fine with either way.

[@rosel8140]

Okay I'm going to check some out to buy them is why. since I obviously can't test drive them I'm trying to do the compression check at least. Never had to do it before always used friends jet skiis. I seen somewhere it was 150 on the seedoos, think that's too high? I'll check for consistency. Do all jet skiis have 4 spark plugs? I didn't think they'd have as many as cars.

[@ryanmcenroe8680]

No, 150 isn't too high, it all depends on the jet ski, my jet ski has 3 cylinders so 3 spark plugs but it varies.

[@rosel8140]

+Ryan McEnroe okay thank you for the information. One last question, where did you get your compression guage? I'm going to check oreilley or auto zone but they're usually expensive. walmart didn't carry any, so maybe online will be the next best thing? thanks.

[@ryanmcenroe8680]

Rose L I rented mine from auto zone. Normally you can ask the assistant there to borrow one and they will charge you the cost as a deposit

[@ryanmcenroe8680]

and they will return the deposit once you return the tool. Or check amazon if you want to buy one.

[@rosel8140]

+Ryan McEnroe okay thank you for the information.

[@StrinePCs]

Your jet ski needs work man. I use multiple gauges to test my skis and on the polaris I always get 125 or higher on the gauge. Also if you are losing compression while the gauge is still hooked up then you need to perform a leak down test.

[@ryanmcenroe8680]

Harley Strine I appreciate it but I sold it already :( I hope to buy another one to fix as a project

[@charlescollins9413]

I’ve got the same jet ski and it’s 115 on all 3. I’m just running it till she blows then I’ll buy a new motor