I started my 25hr inspection on my 912is with an oil change. I did not have a differential pressure tester available at the time. After a short warm up I removed the bottom plug from the oil reservoir and emptied it. The oil was dark but appeared normal and there was nothing visible in it. I saved it in case I want to get it tested. 


I removed the magnetic oil plug for inspection. There were some deposits (see image), more than none, but not a lot. All appeared small in size and nothing was sharp after rubbing between fingers. However, I’m not sure if this looks like more than I should expect for the first 25 hours. 


Lastly, I removed the oil filter. This thing was way too tight. I believe this was from the factory though. I replaced it and tightened it as per manual. I then opened up the old filter. As many times as I’ve changed my car filter I’ve never once opened it. It was interesting. After cutting out the paper filter and letting the oil drip off (left it about an hour) - there were no large deposits of any kind. Running a magnet over it didn’t pick up anything. However, using a flashlight I did see about 10-20 sparkle/glitter sized flakes on the shop towel and embedded in the paper. Is this expected or of a concern? (see images)


After replacing 3 L of oil as per manual I rotated the prop 20+ (about 40) times as I was expecting a burp - but I never got one. Is that expected? Oil level on the dip still remained just about at the minimum. 


I removed all the spark plugs. I believe they look ok. Consulting google I don’t see anything of major concern. Would you think differently? (See Images) I replaced all plugs with a NKGs gapped to 0.032-0.033 in. 


The differential leak test on the 912is took place after my oil change due to not having it available. Starting with cylinder 3 I found TDC using a rubber glove on the end of the connected hose. I slowly increased the pressure to 80psi and it was holding at 78psi. However, I noticed I was getting a gurgling/burping sound in the oil. This seemed very strange. I repeated on the remaining cylinders and noticed the oil gurgling starting anywhere from 10-40psi, although there was no pressure change detected on the differential. My oil reservoir was now nearly flowing over. What’s going on here? Is this expected? I wouldn’t think so. (see video)


During the 25hr (ecu indicated, 28hr timed from engine start) I only used about ¾ litre of oil. There were no other concerns during flight that would cause suspicion. (ie loss of power, sounding different etc).


During visual inspection everything else was ok except for a very small coolant drip (already known) at the connection to the radiator. Additionally it was found that this same hose was rubbing/touching the cylinder fins and had started to melt away the protective sheath in that area. This was fixed by shortening the hose to allow a better (straight fit) onto the radiator connection. This provided a gap at the fins as well as improved the fit which should remedy the small drip. Additionally it was required to shorten the heater core attachment on the T junction of this hose to prevent additional pressure pushing the hose back towards the fins. (See images). 


All other inspection points had no issues. 

Oil Magnetic Plug
This is after oil change and rotation of prop by hand
Oil filter tear down

  • Re: 25hr Inspection 912is - Concerns

    by » one year ago

    Nothing gives me any great concern.

    When you first tried to "Burp" the engine, was the Mag plug still out?
    If the crankcase is not "AirTight" it will not burp.
    40 turns of the prop pumped oil into the crankcase and retuned none.
    A short shot of compressed shop air into the Mag Plug Hole will also Burp the crankcase.

    A new engine has some of the assembly debris. The next inspection should be cleaner.

    The Blowby of the Differential Pressure test is very similar to a running engine.
    You should expect to hear continuous burping and the return of ALL the excess Oil in the crankcase.

    After cutting the Oil Filter open, place the paper filter element in a jar with a sealable lid.
    Add some gasoline to the jar and shake it vigorously to rinse the oil filter element.
    Pour the Gasoline/Oil debris mixture through a white "Coffee" Filter to reveal the filtered out debris.

    ECU Hours = Lane ON Time.
    Hobbs Hours = Engine Running Time.
    ECU Time will always outrun the Hobbs time.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

    Thank you said by: James N Parker

  • Re: 25hr Inspection 912is - Concerns

    by » one year ago

    Everything Bill said. :) 

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

  • Re: 25hr Inspection 912is - Concerns

    by » one year ago

    Yes, plugs were out when trying to burp.... that explains it.

    Also glad that the diff press burping is expected. I was a bit concerned. 

    I'll soak the filter paper and see what's there. 

    As far as hours indicated goes... the ecu engine running time is less than the time extracted from logs in my g3x. It differs by about 3 hours. Is the ecu timer based on a specific rpm? I've been tracking from start time to stop time.

  • Re: 25hr Inspection 912is - Concerns

    by » one year ago

    As a famous man once said, "What we have here is a failure to communicate." ?

    There are multiple timers running on multiple devices.

    There are Hobbs-Type timers.
    These record the time that the engine is running without regard to the RPMs.  ON or OFF!

    Your g3x likely has a Hobbs time that you can adjust to match the Engine total hours.

    The ECU has its own timer that reconds the Lane ON time without regard to the engine,
    The lanes can be ON without the engine running but you can NOT run the engine without a Lane ON.
    Therefore the ECU/Lane timer will always outrun the Hobbs.

    An ECU/Lane and Engine/Hobbs timers are internal to the Rotax ECU Module and cannot be adjusted.
    Both will include the few hours the engine spent on the test stand at the factory and so will show more time than your g3x does unless YOU adjusted the g3x to match.

    I haven't looked closely at the g3x manual but most EFIS panels are similar.
    There is likely a timer for Hobbs Time, Tach Time, Engine Time, and possibly EFIS/gx3 ON Time and Rotax ECU/Lane time.

    So, when you refer to an "ECU Engine Running Time" and an "ECU Timer", what do you really mean?
    Engine Running time (Hobbs) taken from the ECU? 
    ECU/Lane Time?   or
    A Hobbs time from the gx3/EFIS?

    It sounds like the g3x Log timer records the time the g3x is power without regard to the engine operating.

    - - -

    Tach Time is the only timer that references Engine rpm.
    It is really a revolution counter scaled to display as hours instead of thousands of revolutions.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

  • Re: 25hr Inspection 912is - Concerns

    by » one year ago

    Hi all

    Just my take on checking the oil filter paper element.  I was always shown that the easy (fast) way was to cut the element out and make it about 3 to 4 segments in length.  I then fold the pleaded element back together and wrap with several layers of paper towel.  Take this to you vise and squeeze the oil out.  The paper absorbs the oil and the element when you remove it will be almost 100% dry with all the little sparkly bits still sticking to it without the shiny oil in the way.  Up to the 100 hour, even as much as 200 hour, you can expect to see traces of breakin in the filter.  Some of the shiny parts are from the assembly lubes such as Loctite anti seize.  It is rare to find anything ferrous (magnetic) and tiny bits of carbon sometimes find there way to the filter.  

    Just my take on it.



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