A two stroke motor operates on four elements: air, fuel, compression and spark. Obviously, without air, fuel and spark, the motor would not have be able to perform combustion. Compression is created by a piston as it travels upward through the cylinder and squeezes air and fuel into a dense mixture that will ignite with great force. A compression loss can be caused by a faulty seal between cylinder, piston or piston rings, creating a loss of power or ability to operate. Luckily, checking the motor's compression is a simple task.
Things You'll Need
- Compression tester
Remove all of the spark plugs from the motor, and ground the spark plugs against the engine case.
Screw a compression tester into the spark plug hole on the first cylinder to be tested.
Twist the throttle completely open and kick start the motor to move the piston(s). Kick the motor over a few times and look at the compression tester's gauge. A motor must have a minimum compression rating of at least 100 to 125 pounds per square inch to operate properly.
Open the tester's pressure release valve momentarily to clear the gauge, and unscrew the tester from the spark plug hole. Repeat as necessary for the any remaining cylinders.
Tips & Warnings
- For best results, kick the motor over and check the compression. Release the pressure and test again until the results are consistent.
- Refer to a service manual specific to your motorcycle for detailed compression specifications.
- "The Professional Motorcycle Repair Program;" Professional Career Development Institute; 1995
- Dan's Motorcycle: Engine Compression Testing
- Photo Credit Jupiterimages/Comstock/Getty Images
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