fbpx
Login

 

Jump to Forum..

Sudden loss of compression

in 912 / 914 Technical Questions 3 hours ago

Hi folks.

my 912 ULS has around 625 hours on it and after working on the fuel system, I wanted to test the engine and while hand cranking the prop, I noticed a loss of compression on cylinder 1. I identified cylinder 1 by removing spark plugs one by one.
I did my 200 hr maintenance work around 20 hours ago (compression was super on all 4 cylinders) and since then the aircraft was flying without issues.

With two plugs in cylinder 1, I hear air hissing by when I hit the compression choke. I'm not 100% certain but I believe it's not coming out of the oil tank but rather from the carb.

Tomorrow I'll do a real compression test, but any hints what I could be looking at?

Mr Chatty (chatgpt) says valve clearances are 'often' a cause for this - any thoughts on this?

Thanks

Mark

  • Re: Sudden loss of compression

    by » one hour ago

    Hi Mark,

    Good idea to do another compression check before anything else. 

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

      
    Report

  • Re: Sudden loss of compression

    by » one hour ago

    Yes will do. And I will check the rockers for free play.

    Assuming the valve clearances are ok but compression is still low, do you see a risk of running the engine? I'm guessing carbon deposit could be hindering one of the valves  from fully closing but I don't want to risk burning the valve? Not sure how real that risk is? Perhaps running at idle until oil temp is 50C and then rechecking the compression could be a low risk attempt here?

    Yeah, that's quite a few question marks but I'm not an expert so looking for some advice here.

    Thanks!

      
    Report

  • Re: Sudden loss of compression

    by » 51 minutes ago

    Are you using 100LL or auto fuel? If the compression test is good and everything under the valve cover looks good then try a start, but do not let it sit and idle at low rpms.

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

      
    Report

  • Re: Sudden loss of compression

    by » 50 minutes ago

    Auto gas.

    The compression for sure won't be good, that I can feel.

      
    Report
You do not have permissions to reply to this topic.
Related Topics
Title Category Replies
912 UL Low Fuel Pressure and Power Loss 912 / 914 Technical Questions 8
What Compression Tester to Get 912 / 914 Technical Questions 9
Sudden turbo overboost 912 / 914 Technical Questions 1
ECU Errors loss of percentage power and throttle position indicators 915iS Technical Questions 2
Loss of power doing climb 912 / 914 Technical Questions 9
Follow Us

Safety First!

To receive critical-to-safety information on your ROTAX Engine, please subscribe to
ROTAX-OWNER.COM

Login