Re: Cylinder Compression

Posted by JWL On 2010/10/27 9:50:43

This may be too elementary, but when I check compression this is how I do it.

Remove air cleaner

Remove all spark plugs

Ground distributor primary wire (the small one from the coil to the distributor.

Hold throttle wide open, and on a cold engine make sure choke butterfly is fully open too. Generally, compression tests are done on a warm engine, but a cold engine can be tested too.

Insert/install compression gauge securely into spark plug hole, and crank engine at least four cycles until highest reading is obtained on gauge. Gauge reading should increase with each cycle.

Note reading.

Repeat for remaining cylinders.

Look for differences of more than 20% and large differences between adjacent cylinders.

This is for a "dry" test.

For a "wet" test squirt some engine oil into the cylinder and crank the engine without the gauge installed; then repeat the procedure as in the "dry" test.

Compression reading increase over "dry" test is a sign of worn piston rings.

As I said at the beginning this may be too elementary for most, but it bears repeating from time to time.

(o{I}o)