How to Check Your 2 Stroke Engine for Compression


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.

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  • Photo Credit Jupiterimages/Comstock/Getty Images
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