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Hello together!

I've been reading a lot in the forum and have just upgraded my account because I want to ask you for ideas why an engine that has died.

I am a licensed engineer, but not that experienced on Rotax yet, even though I'm of the same country of origin laughing.

Recently I was called to a "hard to turn over" 912S3 100hp. I recognized that besides very high friction during turning, there is a certain blockage to overcome. There was no oil indicated on the dipstick. After opening the oil tank lid I estimated minimum 1.5 liters oil missing. The pressure applied to the cylinders blew straight out of the carburetors and exhaust. So I removed the mugs and found stuck open inlet valves on all four cylinders.

The aircraft owner (a flight club) told that a member started the engine normally, but after e few seconds it stopped and the starter would not crank it again. The last flight was a few days before it without any occurrences. Multiple people are using the plane. Every single one declared to have checked oil level during preflight. The last 50 hrs inspection was 30 hrs ago, done by myself.

What I am really wondering is: How can that much oil be missing? There is no drop of oil outside on the engine, compartment and belly. If the oil was low before, why were there no signs earlier? I don't want to think about, but could it be that it was sabotaged and the oil was sucked out of the tank and only the last unlucky guy did not check? Or is there another explanation for the seized/bent valves and the oil was just low because it was not possible to turn the engine over until gurgling? They said the engine was running less than 10 seconds before it got stuck. Any advises were to have a closer look when I tear down the engine later?

Of course, I am waiting for a new engine now. There is no reason to waste more time on this one. But I am curious what happened.

Thanks in advance for your inputs!

Cheers, Uli

 

  • Re: bent valves on all cylinders

    by » 2 weeks ago


    I will bet the camshaft timing gear is all screwed up and the timing suddenly went way off and bent all the valves. Probably all the missing oil is still in the crankcase. 


  • Re: bent valves on all cylinders

    by » 2 weeks ago


    Read and check out unscheduled maintenance in the line maintenance manual. If the engine was overspeed the hydraulic lifters can start to float on the camshaft, get out of timing with the pistons causing pistons to hit valves and bend them.

    3.4) Exceeding of max. admissible engine RPM

    General note

    5800 rpm up to max. 6200 rpm

    5800 rpm up to max. 6200 rpm

    6200 rpm up to max. 6500 rpm

    6200 rpm up to max. 6500 rpm

    Any exceeding of the max. admissible engine RPM must be entered by the pilot into the engine log book stating duration extent of overspeeding and pertinent detail.

    If the limit was exceeded for max. 1 minute and max. 6200 rpm

    page77image10263888page77image21535104

    1

    Step Procedure No action needed.

    page77image21529344page77image21535296

    If the limit was exceeded for more than 1 minute and max. 6200 rpm

    1

    Step Procedure

    Check that the push-rods are straight.

    page77image21530688page77image21530112

    If the limit was exceeded for max. 1 minute and max. 6500 rpm

    1

    Step Procedure

    Check that the push-rods are straight.

    page77image21536064page77image21536256

    If the limit was exceeded for more than 1 minute and max. 6500 rpm

    Step

    Procedure

    1

    The whole engine must be inspected, repaired or overhauled in accor- dance with the BRP-Powertrain instructions for continued airworthiness.

    2

    Check that the push-rods are straight.

    3

    Inspect the crankshaft for out-of-roundness. See chapter 72-00-00 section 3.9) of the Heavy Maintenance Manual.

    4

    Inspect all systems for correct functioning.

    5

    Detailed inspection of affected engine components.

    page77image21538560

    more than 6500 rpm

    If the speed of 6500 rpm was exceeded

    Step

    Procedure

    1

    The whole engine must be inspected, repaired or overhauled in accordance with the BRP-Powertrain instructions for continued airworthiness.

    2

    Check that the push-rods are straight.

    3

    Check differential pressure.

    4

    Inspect crankshaft with mounted drive gear for runout and distortion. See chap. 72-00-00 section 3.9) and 3.18) of the Heavy Maintenance Manual.

    5

    Check if piston had contact with valve.

    6

    Check roundness of valves.

    page77image21541056

    Effectivity: 912 Series Edition 3 / Rev. 1

    05-50-00

    page 11 January 01/2013


  • Re: bent valves on all cylinders

    by » 2 weeks ago


    The oil is probably in the Pan.

    Remove the Crank locking bolt from the side of the Block and blow compressed air in to pressurize the block. 1 Bar max.

    If there is any Oi; in the pan, it should return to the oil tank with a health "Burp"

    If the engine block will not pressurize, you have/had a leak somewhere.

    Pull the Oil line off the pan bottom and see how much drains out.

     

    I would not think that 1.5L low out of 4 would cause the engine to seize.

    It might have some air in it but it would be good enough for an idle.

    As long as there is at least a few cm of oil in the tank the engine will still be getting lubrication.

     

    As mentioned, the CAM is the major suspect.

    Be sure to let us know what you find.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    whertzel1@yahoo.com
    Clicking the "Thank You" is appreciated by all.

  • Re: bent valves on all cylinders

    by » 2 weeks ago


    Hi all,

    Thanks a lot for your inputs! It makes me confident to take distance from the sabotage theory.

    I first thought about a camshaft timing issues, but skipped the idea because of the engine design.

    I can't confirm the overspeed issue since the clubmembers flying said that everything was fine. That's a bit difficult when many people flying with one plane...

    Will see what we discover when taking the thing apart and I'll post photos.

    Cheers, Uli

     


    Thank you said by: Wayne Fowler

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