help with compression test

[bobjoe1]

I have a 1989 Evinrude 40hp motor and have a service manuel but for the life of me I cannot find the correct compression anywhere. It's a 2 stroke and want to test but don't know what compression is supposed to be.

 

[Black as]

Re: help with compression test

I have a 1989 Evinrude 40hp motor and have a service manuel but for the life of me I cannot find the correct compression anywhere. It's a 2 stroke and want to test but don't know what compression is supposed to be.

try this link http://www.outboardrepairs.com/compression/

 

[Silvertip]

Re: help with compression test

You won't find it in the manual because the numbers aren't published for the following reasons (to name just a couple):

1) Every engine (good ones even) will test differently
2) Every gauge (cheap ones, good ones, and those in between) will read differently
3) Everyone tests differently
4) Too many engines are torn down because someone hit the panic button.
5) A leak down test is a better indication of engine conditon. (Search for it on-line)

So -- if engine compression is higher 100 psi or more and all cylinders are within 10 - 15% of each other you are good to go. An engine with lower than 100 psi but very even compression may still run very well and be down on power very little.

If you do find low compression, DO NOT panic. Decarbon the engine and retest. The decarb procedure is discussed in great length in this forum. Search for it.

 

[5150abf]

Re: help with compression test

Buy a gauge and test with only that gauge, as mentioned diffent gauges will read differently.

Also you should check the engine when it is hot but a cold reading will work to just do it the same every time.

As Silvertip said 100+ is great but less will work too, being close in both cylinders is the most important, I have an '81 50 that has 120 cold-135 hot- both cylinders and I will check it once or twice through the year just to keep an eye on the engine.

A decarb is a good idea either way, it has probly never been doen and will help the engine run better regardless.