Compression Testing a 2.7 with Carbs
 

Hey Guys,

Bought a nice compression tester last fall and with the weather warming up this weekend I figured I would try it out on the car. Obviously I am going to disable the fuel pump but have questions on the engine prep before the test.

My thoughts are to run the test with a cold motor and all plugs in. Is this correct? I figure with the plugs in the back pressure would be more like actual operating conditions?? I have also read that the plugs should be removed cold due to expansion and possible damage to threads on a warm engine???

What procedures are correct?

I've always done compression tests with all the plugs removed for two reasons. First the tester screws into the spark plug hole so removing them makes sense and second the starter can spin the engine more easily with them removed so the readings are usually more accurate.

Oops, one more thing. Yes it is better to remove the plugs cold on ANY aluminum cyl. head.

I like to unplug the CD,
keep throttle WOT

Warm engine to operating temperature
Remove all plugs
Ground the coil wire (remove from distributor cap)
Open throttle
Crank engine for 4 compression strokes (go 8 if you have an early S or with agressive cams); record the last reading

Sherwood

This is tomorrows job finally.
 

The big question, hot or cold when running test? Plugs in or out?

normal operating temp, plugs out, crank each cylinder about 10 pumps or until the gauge stops moving.

Should I back the plugs out a bit prior to running the motor up so the removal is easier and I do not damage the threads?