I've noticed a few posts on compression lately and thought I'd make a reminder on compression testers........

Are you sure it's reading correctly?

And it's just not the gauge you need to worry about.

Compression testers use a schrader valve (tire valve core) to capture the pressure. It takes a certain amount of pressure to open that valve which will lower the reading on your gauge by that amount....

(Once upon a time my gauge started leaking and I replaced the valve to find the readings went down by 25psi, which is how I found this out........... (swapped in another valve which didn't take so much pressure to open up))

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Interesting! I think I have 2 I got at a yard sale. Even came with a tool to change the valve.

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'72 Duster 198 stock cam, 3:23's Hookers on jack stands for 8 years in the driveway
'79 Maxivan 360 Offy Qjet Comp RV cam/rusting in the driveway.
93 D350 160HP Cummins Auto Dually Clubcab needs a injector pump
2005 Golden Couch Buick

also I believe the starter spinning torque will have an effect on the compression---- faster spin higher torque-- my guess as to why it is more important to have equal numbers vs high numbers

To do a correct compresion test one must remove all the sparkpulgs and open the carb plates some. A good compression guage is a must. Ie Snap On Mac or Crfastman. With all plugs removed turn the engine over until the max compression is reached. Rotate the engine until it reach the max psi. Thanks Ron Parker








Im A Hokie