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Compression Check

  • Buy an automotive style compression tester from an auto parts store.
  • Run the engine for a minute or two so it is slightly warm and has oil throughout
  • Remove all 6 wires from the coils (Be gentle with the locking clips)
  • Remove all six coils by loosening bolts until coil pulls off the spark plug
  • Remove spark plugs with 5/8 sparkplug socket. Hold tool straight to prevent braking the plug
  • Screw compression tester into one cylinder until seated against the O-ring on tester
  • Open the throttle fully
  • Stay clear of the propeller and tie the airplane down
  • Provide power to the starter switch but leave the ignition off.
  • Press the start switch and watch the needle on the compression tool. It will stabilize after a few seconds of cranking and not increase any more.
  • Write down this reading. It will be somewhere between 180 and 230 psi.
  • Repeat the test on the rest of the cylinders (Be sure to reset the tool by pressing the button and release previous pressure)
  • Below 180 - clean engine with marvel mystery oil in the gas / use auto fuel only for a while
  • 180 to 190 is good
  • 190 to 210 is great
  • 210 to 230 can't get better and be sure to use good quality fuel
  • Reinstall spark plugs with a small amount of anti seize on the second and third thread of the plug (stay away from the electrode)
  • Tighten new plugs until the built-in crush washer is compressed. You can feel it compressing.
  • Tighten older plugs (washer already compressed, until snug against the block, then 1/8 turn)
  • Reinstall coils
  • Reinstall coil wires
  • Close the throttle
  • Record results in the engine logbook