Compression testing...

[sirdave4]

I had recently purchased a compression tester (craftsman) and wanted to test the compression in a 89 Waverunner. After reading the directions, I found that there was an option of performing a wet or dry test. For the dry test it's pretty self-explanitory, but what I was wondering is if a wet test would be advisable in a 2 stroke engine? I'm not sure how common the terminalogy "wet test" is but the directions say it removes the influence of the piston, piston ring and cylinder. You simply drop a teaspoon of motor oil in the spark plug hole and repeat the dry compression test. Listed below is the outcome...

1. If the reading is greater than the initial dry test then air is leaking around the worn or damaged piston rings.
2. If the reading are the same of both the wet and dry test, then the valve, valve lifters or camshaft lobers is worn.
3. Any lower reading of cylinder compression indicates worn or damaged parts.

Another question I have is what would be considered a perfect test?

[sirdave4]

Re: Compression testing...

The main reason I'm going through all this hassel is to make sure the engine is sound before sinking any money into the ski. Is a compression test one of the best ways to determine the overall condition of the ski's motor? For the dry compression test, all I did was remove the spark plug, screw in the gauge and let the motor turn over 5 or 6 times. The results came out to be approx 135 in both cylinders. The factory specs are 150. Does this little test give me any assurance that the motor is in somewhat good shape?

As you can see, I'm diving into unkown waters and any advise would be greatly appreciated. Thanks in advise for the help...

[Skipper]

Re: Compression testing...

Two strokes don't have valves (I bet you already knew that). Also two strokes mix oil into the cylinder for you so it probably would not help to add more oil for the test.

The wet test is a valid test for four stroke engines, just like you described.

[sirdave4]

Re: Compression testing...

If the compression test comes back as 135lbs, is that a valid tesst? If so, does that give me any idea of how the overall condition of the engine is?

[surveyguy]

Re: Compression testing...

did all cylinders come in at 135? Being equal is most important. Of course you want it as high as original as possible, but you don't want any cylinder much more than 5% difference than another.