Compression Gauge now what??

buckstop108

Seaman
Joined
Aug 2, 2007
Messages
67
:redface: I got my hand on a compression gauge. Now what? Do I take all the plugs out at once or one at a time. If I pull the clip on the kill switch would this be ok so the engine doesn't start. This is a follow up post from the water issue "I Don't Think It's water". Thanks for all the help. If the compression checks and all the cylinders are getting spark, am I back to a carb problem causing the misfire and not burning the fuel?
 

Walker

Captain
Joined
Jun 15, 2002
Messages
3,085
Re: Compression Gauge now what??

Yes, pull all the plugs and pull the safety lanyard off.
 

HighTrim

Supreme Mariner
Joined
Jun 21, 2007
Messages
10,486
Re: Compression Gauge now what??

If you're going to set a benchmark, Ive always been told to bring the motor to operating temperatures first. Although this has caused much discussion on here. Pull all the plugs. Pull the kill lanyard. Screw the gauge in one cylinder at a time, turning over 6 to 7 times roughly or until the gauge reaches its "peak". Record reading. Test remaining cylinders.
 

GeneH

Petty Officer 2nd Class
Joined
Sep 1, 2007
Messages
109
Re: Compression Gauge now what??

Don't forget to open up the throttle so the engine can get some air to compress!!! With closed carbs, compression will check low.
 

wildmaninal

Lieutenant Commander
Joined
Jul 14, 2007
Messages
1,897
Re: Compression Gauge now what??

I heard that there is a better way to check the cylinders other then a compression Gage, using an air hose to fill one of the cylinders to 100lb or so then see how long it takes for the cylinder to loose it's compression/pressure or something like that then repeat to the next cylinder. If it looses it's peak (100lbs of pressure) quick then it is a bad cylinder, if it looses it slowly over a period of time it is good. But I believe this is a procedure that some mechanics would use in a shop. I've heard that you can blow seals doing the check this way. It wouldn't be hard to setup a valve stem to put into the spark plug hole fill the cylinder to a point as wanted then check it with a tire gage over a 10 to 20 minute period if not longer.
 

BoatBuoy

Rear Admiral
Joined
May 29, 2004
Messages
4,856
Re: Compression Gauge now what??

Doesn't really make any difference about the throttle. It makes a difference in 4-strokes, but not 2-strokes. They'll take a breath through the exhaust ports at cranking speed.
 

pgdignan

Petty Officer 2nd Class
Joined
Jul 31, 2007
Messages
142
Re: Compression Gauge now what??

Wildanimal, I think what you're describing is a "leak down test".
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: Compression Gauge now what??

i follow hightrim's procedure, all guages are different and register a little different. i use it for a base to work with, and keep a record for future maintainance. the main thing is that the numbers are withing 10% of each other, one low cylinder over work the others and will bring the motor down. sometimes a really good decarb with seafoam will free up rings and bring the low cylinder back into range.
 

wildmaninal

Lieutenant Commander
Joined
Jul 14, 2007
Messages
1,897
Re: Compression Gauge now what??

Wildanimal, I think what you're describing is a "leak down test".

I couldn't think of the name of the procedure to save my life. I was discussing compression test with somebody and they had mentioned the leak down test was better then the compression test in there opinion. I imagine that it is doing the same thing right, just without the engine turning over.
 
Top