Proper compression

[Steelranger2]

So today I did a compression test on cylinders 2,4,6 and on 2 and 6 they had a compression of 185 lbs with the middle one at 150..Does anyone know what the compression is soposed to be?

 

[luigisho]

http://www.shoforum.com/index.php?threads/compression-specs.57506/

 

[rubydist]

the actual numbers you get will vary widely depending on the accuracy of the gauge and the speed of cranking. you would like to see values within 10% of each other, your numbers are 19% so the middle one is a little weak.

these engines are notorious for getting stuck rings, so I would run some seafoam in the engine, and then change oil to Motorcraft semisynthetic and drive it for 5000 miles and test again. I've had really bad stuck rings loosen up on a couple of oil changes using the Motorcraft semisynthetic oil.

 

[sperold]

Does the compression test gauge have a screw-in end or a rubber bung arrangement? Each have their issues, but the rubber end thing is hard to use.

 

[Steelranger2]

It has a screw in end, I was thinking that maybe carbon buildup could cause this.


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[rubydist]

yes, carbon builds up in the ring grooves and eventually the rings get stuck and don't move any more. they get forced inward to the point required for the highest temperature the piston ever experienced, which means they are loose most of the time. that results in piston rattle, lower compression, lower power, and increased oil consumption.