Compression test

[01walter]

I had my engine (SX200TXRB) winterized and they did a compression test - 105-110 in each cylinder. A test run a couple years ago showed 125-135 - should I be concerned or is this normal wear and tear or normal variability for the compression test?

[DennisG01]

There's a lot of variables that come into play (cold or hot engine, the compression tool being used, even the person doing it, etc) and it's hard to give a specific answer. The important part is that all the cylinders were close to each other. BUT, if the tests were done under 100% identical conditions (including a verified tester) then the difference you see would not be normal as that's a significant drop. Don't get too concerned - it is EXTREMELY unlikely that the conditions were identical. Extremely unlikely.

[boscoe99]

More than likely it is a variability due to one or more differences. Gauges can indicate differently and the test procedure used can vary.

Battery should be fully charged, motor hot from recently being run, throttle wide open, all plugs removed and the motor cranked until the pressure stops rising.

Different mechanics don't always do the test in the same manner. You might want a third test for a tie breaker.

You are well above Yamaha's minimum specification with either test.

[DennisG01]

I should also add (and maybe someone more knowledgeable can confirm/deny) that it's also highly unlikely that IF wear/tear caused those numbers... that they'd still all be so close to each other. Usually one or two cylinders will show a lower number if there's been issues - not all of them so evenly.

[01walter]

Thanks for the feedback - I thought there should be reasons for the change and thats enough for me to rest easy until spring. Thanks again and happy holidays!

[TownsendsFJR1300]

I just recently purchased a very good compression tester to replace a very old Sears unit I had. Screw in hose, adaptors, o-ring seals, etc.

While playing with and testing the compression in two separate weedeater engines (small 2 strokes, both cold), my best running engine showed about 195PSI. the one that always ran crappy, 135 PSI.

My old tester wasn't accurate enough (you had to physically hold it in the spark plug hole). The unit, as noted above makes a BIG difference on getting an accurate reading..

http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1