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Diagnose this Engine Failure With Pictures

in General Tech Discussion 11 years ago
Hello,

I have attached some pictures of one of our engines 912 ULS which had suffered loss of power in one of the flights.

A little background:
Engine is 10 years old
500+ hours
Reasonable operators

The story:
During one of the routine flights, the pilot felt loss of power and landed immediately.
After a brief check on the engine, we discovered a loss of compression which lead us to open this engine and find out this.. Please see the attached pictures of the piston and cylinder head # 2.

Questions:
1) What could have lead to this serious engine failure? (Heat, Premature Ignition, Loss Of Oil Etc..)
2) What would you do.. Do you suggest repair or replace the entire engine?

Your valuable opinion is highly appreciated.

Thanks,

Andre'




912ULSFailure.jpg (You do not have access to download this file.)

  • Re: Diagnose this Engine Failure With Pictures

    by » 11 years ago

    Hi Andre,

    Detonation. It can be repaired.
    What fuel were you using, how old a fuel, what octane, what notch was the needle clip placed?

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

      
    Report

  • Re: Diagnose this Engine Failure With Pictures

    by » 11 years ago

    I agree with Roger: its clearly detonation. You could have got a shot of methylene (used for cleaning the fuel delivery tanks and pipes) or some diesel fuel mixed in with your gas?
      
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  • Re: Diagnose this Engine Failure With Pictures

    by » 11 years ago

    Typically detonation happens in one cylinder first. The circumstances are just right to happen in one, but usually doesn't happen in 2 or more at the same time. This looks like a typical detonation problem. I have seen several from people not following Rotax recommendations and doing their own thing. I don't think anyone knows yet what caused this, but I hope they report back and let us know. It is very costly.

    Quote:
    Detonation occurs when excessive heat and pressure in the combustion chamber cause the air/fuel mixture to auto-ignite. This produces multiple flame fronts within the combustion chamber instead of a single flame kernel. When these multiple flames collide, they do so with explosive force that produces a sudden rise in cylinder pressure accompanied by a sharp metallic pinging or knocking noise. The hammer-like shock waves created by detonation subject the head gasket, piston, rings, spark plug and rod bearings to severe overloading.
    Mild or occasional detonation can occur in almost any engine and usually causes no harm. But prolonged or heavy detonation can be very damaging. So if you hear knocking or pinging when accelerating or lugging your engine, you probably have a detonation problem.

    Try a higher octane fuel. The octane rating of a given grade of gasoline is a measure of its detonation resistance. The higher the octane number, the better able the fuel is to resist detonation.

    "Read" your spark plugs. The wrong heat range plug can cause detonation as well as pre-ignition. If the insulators around the electrodes on your plugs appear yellowish or blistered, they may be too hot for the application.

    Check for engine overheating. A hot engine is more likely to suffer spark knock than one which runs at normal temperature. Overheating can be caused by a low coolant level, a slipping fan clutch, too small a fan, too hot a thermostat, a bad water pump, or even a missing fan shroud. Poor heat conduction in the head and water jackets can be caused by a buildup of lime deposits or steam pockets (which can result from trapped air pockets).

    Check for a lean fuel mixture. Rich fuel mixtures resist detonation while lean ones do not. Air leaks in vacuum lines, intake manifold gaskets, carburetor gaskets or the induction plumbing downstream of a fuel injection throttle can all admit extra air into the engine and lean out the fuel mixture. Lean mixtures can also be caused by dirty fuel injectors, carburetor jets clogged with fuel deposits or dirt, a restricted fuel filter or a weak fuel pump.
    If the fuel mixture becomes too lean, "lean misfire" may occur as the load on the engine increases. This can cause a hesitation, stumble and/or rough idle problem as well.
    The air/fuel ratio can also be affected by changes in altitude. As you go up in elevation, the air becomes less dense.
    A carburetor that's calibrated for high altitude flying will run too lean if driven at a lower elevation. Altitude changes are generally not a problem with engines that have electronic feedback carburetors or electronic fuel injection because the oxygen and barometric pressure sensors compensate for changes in air density and fuel ratios.

    Change your flying habits. Instead of lugging the engine, try less prop pitch.

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

      
    Report

  • Re: Diagnose this Engine Failure With Pictures

    by » 11 years ago

    I had a piston failure in flight attributed to a broken ring. Ring piece entered combustion chamber and brinelled the head and piston, looking very similar to your failure. In fact, if I'm seeing pics correctly, it appears that part of your top rng is missing. My ring was most likey pre-fractured 7 years ago when I installed the high comp pistons into 912, yet ran fine for 700 hrs.
    The black color of your piston indicates a rich mixture which over prolonged time, may clog rings and contribute to failure. I'm not convinced you had a detonation failure.
      
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  • Re: Diagnose this Engine Failure With Pictures

    by » 11 years ago

    It's too eaten out in one spot. A ring bouncing around would have tagged more of the piston top. this is too concentrated. I have seen several and they look just like this.

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

      
    Report
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