How to Compression Test a Yamaha 60 Outboard

A compression test is essential to understanding your outboard’s health. It allows you to measure how healthy the individual cylinders and the engine itself are.

Performing a compression test is a good idea when evaluating a used outboard you’re thinking of buying. It’s also an ideal first step for diagnosing engine problems. Here’s how to do a compression test on a Yamaha outboard engine.

Tools - Yamaha 60 Outboard Compression Test

• Compression test set
• Spark plug socket and ratchet

NOTE: The steps for compression testing a Yamaha 60HP outboard are the same or similar for all outboard engines. We tested our Yamaha T60 outboard with a Motion Pro compression test set, which is available on our sister site Partzilla.com. 

Outboard Cylinder Compression Test

Step 1. Start the motor and let it run for a couple of minutes to come up to temperature. 

NOTE: If you can’t start the motor and you’re testing it cold, expect your results to be a little bit lower than they would be if the engine were warm.

Step 2. Open the throttle bodies so the engine doesn’t have to fight to pull air past the plates. 

NOTE: We manually pushed the throttle open, then used the cap of a pen to hold it in place.

Step 3. Disconnect all the plug wires and remove all the spark plugs. 

NOTE: If you have a fuel-injected engine model, disable the fuel pump so it doesn’t drown the cylinders. This may mean disconnecting a fuse or disabling a relay, so check your service manual first.

Step 4. Choose an attachment from your compression tester that fits your outboard’s spark plug opening size. 

Step 5. Connect the hose and the compression tester. Thread the hose into the first spark plug opening while leaving the others open and then attach the tester. 

NOTE: This step may differ slightly if you’re using a different brand compression tester.

Step 6. Turn the engine over several times as if you’re trying to start it. The needle on the compression tester gauge will fluctuate as you turn the engine over, and then stabilize at the pressure for that cylinder. Record the results.

Step 7. Disconnect the tester, then move it to the next cylinder and repeat the process for all of the cylinders on your engine. 

NOTE: The 220 you see in the image above is where we recorded the results from our first test. Be sure to record the results for each cylinder as you move through the process.

How to Read Outboard Compression Test Results

Check the service manual on your outboard for the precise specifications. Remember that if your engine is cold, the results will be slightly lower. 

• Good results for a two-stroke engine are between 110 and 130 PSI. 
• For a four-stroke, good results are between 180 to 210 PSI. 
• Older engines generally fall on the lower end of these scales, while newer engines fall on the higher end. 

Just as important as the individual cylinder results is the consistency you find across all cylinders. You shouldn’t see more than a 5-10 percent variance between cylinders. If the expected results have too great of a variance from what the service manual indicates, you need to find the problem (usually a leak) and immediately service your outboard engine.