Compression test

[brother chris]

I want to do a compression test on my 78 55hp rude. <br />The thing is, I've read alot of postings here, and I do have a manual, but gotten confused at bit.<br />To do a compression test, you have to have the motor at normal operating temp, ground the wires to the motor, and do compression test at WOT. <br />Okay, now the question I have is can I do the compression test with a garden hose attachment or put leg in a bucket of water, or do I have to do it at the lake, since it has to be at WOT. Because I have heard that you should not put motor at WOT when it is on a hose. That is correct right? <br />So if that is correct, then do I have to take the boat to the lake to do compression test? I am sure the mechanics don't do that to all the motors they fix. Or maybe that is why the bills are so high?<br />Anyways, can it be done in my back yard in a bucket? <br />Thanks guys

 

[ob]

Re: Compression test

Brother chris ,you will be performing this test without motor running .Ground plug wires,remove spark plugs,position throttle wide open ,and crank engine over to obtain reading.Each cylinder will be read separately as you will have to move guage from one to the other.This guage will adapt to your threaded sparkplug holes.Start motor on hose and prewarm before beginning test.

 

[fshng4]

Re: Compression test

OB,<br /><br />Could you explain the WOT. How and why it is required to have the throttle wide open.<br /><br />Thanks

 

[ob]

Re: Compression test

So that stroking cylinders are recieving full non restricted intake.

 

[fshng4]

Re: Compression test

OB,<br /><br />Could you explain that a little more in layman's terms. Your explanation is a little to technical for me as I am not a mechanic.<br /><br />Thanks

 

[ob]

Re: Compression test

Think then of stroking pistons as an air pump.If the intake side of the air pump is closed off there is no or little air to compress in cylinder ,hence resulting in low and inaccurate readings.

 

[fshng4]

Re: Compression test

OB,<br /><br />Thanks. I understand now. Good analogy

 

[brother chris]

Re: Compression test

Thanks ob. I don't know why I thought I had to go to the lake to do this <br /> Sometimes I think I am smart and that I know things, well today is just not one of them. <br /> Thank you for the advice, much appreciated