I'm wanting to find an older boat to fish out of. Just sold my 08 Tracker 170TX at the start of summer to pay for house remodel project.

I've got burned before on buying old boats by not checking compression. So this time I want to test compression out on any boat that I look at.

My question is what is the correct procedure on checking the compression. Do a search on the Internet & you can find 20 different answers that contradict each other. Any help/comments greatly appreciated.

Disable the ignition and bump the motor over a few times checking each cylinder. The most important thing is all cylinders should have very close readings. A leakdown test is a better overall test, but an air compressor is needed for it.

Bring it up to temp before you do the compression and leak down check. Pull the plugs, disable the ignition and spin the motor over several times to check each cylinder.

Best thing you can do, is take it to a boat repair shop, for a complete check before purchase.

Looks like your on your way to 20 different answers on here. I never heard that the motor needed to be warm. Maybe on of the experts will chime in.

leak down test is better if you can aquire a gauge

Warm/cold, throttle open/closed doesn't make much difference. It's gonna show if its healthy or not anyway ya check it. Ya gotta have a KNOWN good guage and good battery ta start with. Leak down is better, but ya gotta have tha stuff ta do it with........T

A healthy engine will all have very close numbers out of each hole. If for whatever reason one jumps out different, then the warm up/leak down/throttle open will possibly show it's not cancer but something minor.

Steps to test compression.
1. Get good battery and compression tester.
2. Unhook all the wires from the plugs.
3. Hook up battery.
4. Remove on plug at a time, insert compression tester and crank engine for about 2 seconds.
5. Record PSI on a piece of paper and move to the next plug replacing the previous plug.

You want all reading to be with a few % of each other.

Just one other thing. If your gonna use tha key ta turn it over be sure ta pull tha kill switch lanyard. If your usin' a remote start button its all tha better.............T

Thanks for all of the comments.. All information is appreciated...

+ 1 on this as the right way except I pull all the plugs and then test, no chance of an accidental start, not as hard on the battery/starter to turn over and it will still test the same.
best bet is to take to a GOOD mechanic and let them check it out for you, tell the seller if you buy it they need to deduct the cost from the purchase price (unless your already happy with the price).

Just remembered one more thing. If you use tha key without tha kill switch pulled, groung tha plugs or plug wires just ta make sure ya don't damage any of tha electrics.................

I'm a facotory trained marine tech and perform this task eveyday.
Warm engine with the throttle plates wide open,( to give it as much air as it can get ). All plugs removed, and a hot battery,( so it will spin as fast as it can ). Kill lanyard pulled, ( so it will not ignite any fumes exiting the cylinders.
Record the readings. If more than 15 PSI difference in any two cylinders, There is NOTHING you can do , short of rebuilding the powerhead.
Hope this Helps

One of the reasons you hear people say don't worry about the numbers themselves, just note the difference between cylinders, is because there's so much variation in methods, and gauges, we might all get slightly different results -- the important thing is to be consistent.

Engine at operating temp for sure.

Spark plugs out for sure (better cranking RPMs).

Disable spark for sure; either pull the emergency lanyard, or else use jumper wires to ground the spark plug leads. Floating plug leads can blow a powerpack.

If you get a bad reading on a cylinder try again, just to rule out the possibility of operator error.

Many say to open the throttle -- I have found in my experience that with a 2-stroke it makes no measurable difference.

I've heard that the difference in compression results with the engine cold and warm has some significance, but I can't remember what it was...............