how accurate are they on a motor that is out of the car? Would a dented oil pan / pick up skew results?

Im thinking you cant really get a good compression on a motor that has been sitting for god knows how long, but I may be wrong.

Total newbie at this so any information is greatly appreciated.

Monty

 

ok if it has bad compression it has bad compression.

 

get the engine to normal op temp, remove the sparks, install the compression tester in #1, crank the engine by hand with the motor off 6 revolutions. If it is kind Repeat in each cyl. A healthy engine will get up to comp. Quickly, slow numbers come from bad valves, rod bearings or piston rings. Check with a tech as to his opinions once you get your readings.


[Modified by MikeSarr_GSR, 11:43 AM 4/28/2002]

 

Rod bearings?????????? How can rod bearings cause low compresion readings?

 

I crank until the needle stops moving

 

Proper comp. test should be done with the eng. warm. Since it's out of the car, you can't do that. BUT if the numbers are within 10% of each other doing it cold, you have a good chance. A dented pan (and maybe the oil pick-up, also), must be repaired before installing the engine. It can easily pinch off most of the oil to your engine if u run it that way.