i just bought a engine compression tester from ebay. how do i check the cylinder compression? i know i connect it to the spark plug hole, but then what? ive never done this before so some info would really help.

for those of you who have read my previous posts in this forumn, you read that a mechanic told me that i had compression loss in two of my cylinders on the passenger side. ive learned that if those two cylinders are side by side, that my problem is probably my head gasket. i just want to measure the pressure so i can be sure.

finally, what is normal cylinder compression for a 305?

any help would be greatly appreciated.

 

Remove all of the sparkplugs. Unplug the power wire to the ignition (coil or distributor). Hold the throttle full open. Attach the compression tester to the first cylinder's spark plug hole. Turn the engine over with the starter so that you get enough pressure pulses on the gage that the needle doesn't go higher with the next pulse (usually 3-5 cycles). Record the cylinder # and pressure. Put the gage in the next spark plug hole, make sure you've released the pressure from the previous cylinder, and repeat until you have all 8 cylinders done.

Now, squirt a little engine oil into the first cylinder's spark plug hole. Turn the engine over a couple of times, then connect the compression tester and repeat the test. Remove the tester, squirt a little oil in the next cylinder's spark plug hole, turn over a few times, connect the gage, repeat the test for all cylinders. This is the "wet" test, and you compare the results to each cylinder's dry test. If the pressure of the wet test is significantly higher than the dry test results, you have a piston ring problem. If it is essentially the same, you have a valve or other leak problem. As stated, two adjacent cylinders with similiarly low pressure indicates a blown head gasket.

I'd expect at least 135 psi for the dry test.