Compression Tests

[Barrometer Soup]

There's been a lot of discussion of the importance of compression tests. <br /><br />Just so we're all on the same page, what is the correct proceedure for doing a compression test?<br /><br />I've also heard of the leak down test. Can that also be done by the average backyard mechanic that most of us are?

 

[DHPMARINE]

Re: Compression Tests

I'll probably loose my shirt on this one .... but here goes !<br /><br />I do my compression testing cold and throttle shut.For no real reason.Just do.<br /><br />If the numbers are bad,they won't be all that great when warm and throttle open.And the motor will run poor cold.<br /><br />I do my spark testing with the plugs IN ! Having spark tested with the plugs OUT is not the way we start most motors.They need the spark with the plugs installed.<br /><br />Leak down test is a nice idea,but we already know there is an internal problem,and it still has to come apart for an estimate.<br /><br />DHP (ducking down)

 

[vano6990]

Re: Compression Tests

I just did mine on my 1977 115hp evinrude. <br />1) Started and ran till it reached normal operating temp. Turned off<br />2) loosened all four spark plugs 1/4 turn.<br />3) pulled #1 attached the pressure gauge and cranked a couple of times (till the needle stopped moving) and recorded the reading.<br />4) replaced #1 and pulled # 2 etc.<br />The readings should be with in 10% of each other. <br /><br />This is how I was instructed to do the compression test! Hope it helps