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10 Tips for a Safe and Successful Compression Test

  1.  Run the engine.
  2. Check the mag switch for proper grounding.
  3. Be sure your compression testing equipment is calibrated.
  4. Use a helper!
  5. The person holding the prop is in charge.

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6.  Helper:  Don’t hook the hose to the cylinder fitting until instructed to do so.

7.  Don’t let go of the propeller until the hose has been disconnected from the cylinder.

8.  When finding compression stroke positions, turn the prop in the opposite direction of normal rotation to avoid snapping the impulse coupling. (Tip:  For 4 cylinder engines, if you use the reverse firing order, 4-2-3-1, you only need to turn the prop 1/2 turn when going from one cylinder to the next.)

9.  Finish with cylinder #1.  That way you will be ready to check mag to engine timing.

10.  Examine any questionable cylinders with a borescope.

References:

AD 76-07-12

AC 43.13-1B

Continental Motors SB 03-3 (Compression Testing and Borescope Inspection)

14 CFR 43, Appendix D (Scope and Detail of a 100 Hour or Annual Inspection)

Bonus Tip (Not in the Podcast):

Buy, or make, enough fittings (you can use old spark plugs) so that you can put one in each cylinder before starting the compression test.  Then, you can just go from one to the next without needing to transfer the fitting from one cylinder to the next.

Have a great week, and let me know if YOU have a compression testing tip.