Checking your engineís compression is a key indicator in diagnosing the health of your engine. Doing this test on a four cycle engine will reveal if the valves, valve seats, pistons, piston rings, and head gasket are in good working condition. It will also demonstrate whether or not these items are wearing evenly. In a two cycle (PWC) engine application there are no valves in the combustion chamber, but the test will still let you know the condition of your pistons, piston rings, and head gasket. Healthy engine compression varies widely from manufacturer to manufacturer but all should have a minimum compression of 100 psi per cylinder. Variation between cylinder pressure readings should be no more than 10%.

With a compression tester, a few hand tools, and 20 minutes, you can check this yourself. Before starting the test, warm up the engine to normal operating temperature for most accurate results.

STEP 1: Remove the fuel pump and fuel-injection fuses (fuel injected engines only). Disconnect the main wire to the coil and spark plug wires or ground spark plug wires. Then remove spark plugs.

STEP 2: Start the threaded end of the compression gauge in a spark plug hole and lightly tighten by hand.

STEP 3: Turn the ignition on, open the throttle completely, and crank the engine for several revolutions. This should result in a stable reading, if not, crank up to 10 revolutions, but do the same with all cylinders.

STEP 4: Mark down the results for each cylinder and compare to one another.

TIP: For a cylinder below 100 psi, pour 1 teaspoon of engine oil into the plughole and retest. If the reading jumps, the piston rings are worn. If not, your valves are a problem.

If your PWC engine feels a little sluggish or isnít giving you the power youíre used to, do a quick compression test. It will save you a lot of trouble and money if you trouble shoot early on.