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Lately I have had difficulty in starting since cold weather began.

I hand crank engine as per burping procedure.

Noticed low compression whilst pulling prop through.

However when engine eventually runs, I stop engine after 15min and hand crank engine. Compression feels perfectly normal.

What can cause low compression when cold before starting?

  • Re: low compression until starting

    by » one year ago


    Any thoughts or ideas? Same question puzzles me too...


  • Re: low compression until starting

    by » one year ago


    What are the results of a leakdown test on the cold engine?


  • Re: low compression until starting

    by » one year ago


    i did a research project on this with a dozen planes years ago. I did a compression test when it was hot ehn again the next morning when it was cold. Because Rotax has nice tight tolerances vs Continental or Lycoming the differences in hot vs cold on the Rotax was anywhere from no difference to 1 psi. I have over the years seen engines where the initial test was only 87/70, but just running the engine for 2-3 minutes had it come right back up to normal. That didn't mean something inside was broken it just needed a little alignment change with rings with a quick run.

    I'm old school so I still tend to use 87 psi test pressure, but 80 psi is good too.


    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


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