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Thread: 912 engine rotation torque

  1. #1
    Senior Member HighWing's Avatar
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    Default 912 engine rotation torque

    I have a friend that recently acquired an airplane - not Kitfox with a Rotax 912ULS and during a condition check, the A&P mentioned that he always checks the rotation torque. Since my first flight in 1998, I have never heard of this procedure. The thing that brings up the question is that he mentions that the torque typically increases with engine hours and when it reaches a point action is necessary. My experience over the years is that with hours, the compression tends to increase, as with more precisely seated piston rings and valves, the number of blades turned to burp the oil tank increases due to less blow by. A natural consequence of less blow by, in my mind, would be higher compression resulting in a higher rotational torque. Question - is checking rotational torque a recommended procedure? Other thoughts?
    Lowell Fitt
    Goodyear, AZ


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  2. #2
    Senior Member Dave S's Avatar
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    Default Re: 912 engine rotation torque

    Lowell,

    Sure others have some thoughts, I'll share a few.

    I do not ever recall seeing the term "Rotational torque" per se, occurring in any rotax documents, if we are talking about a 912ULS.

    Contrary to notions that "rotational torque", whatever it is, increases with use/age, my experience with piston engines used in a number of machines (cars, trucks, planes, tractors, lawn mowers, just about everything else) is that they get easier to spin over with age due to wear & reduced compression (cylinder & ring wear & valves). Blowby is usually higher, not lower. In the short term during break in turn over effort increases maybe, but not in a high hour engine.

    There are some things that my manual says to check on the 912uls, two of them torque values - neither are called "rotational torque" (is there such a thing as "linear torque??).

    1) Slipper clutch torque - lock the crank and determine what the breakout force in inch pounds is for the slipper clutch. Since earlier engines do not have a slipper clutch, this is not done in those cases.

    2) Overload clutch - Lock the crank, secure the engine - Torque required to break out the overload clutch - several hundred foot pounds to slip over the cogs.


    Only other gearbox routine measurement, I am aware of, is gear lash.

    If we are talking some other aircraft engine not a rotax - the appropriate manuals would be the place to go.

    FYI - the only case I have seen increases in compression with senior engines is if they have combustion chambers loaded up with carbon one/or lead deposits. - usually evident from the clattering of preignition under load.

    "Rotational torque" is something new to me.....possibly a colloquial moniker?
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  3. #3
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    Default Re: 912 engine rotation torque

    All torque is a rotational measurement. The question is - what is he measuring the torque of and what are the manufacturers limits for that component?

  4. #4
    Senior Member Slyfox's Avatar
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    Default Re: 912 engine rotation torque

    sounds like he is checking for a problem with the case and bearings on the crank. it's called something I just can't think of it. Larry Wenning knows of this, he had a friends plane that had this problem. this is the only thing I can think of that this a p is thinking of. of course that would mean an oh of the engine and correct the problem with the case of the engine.
    steve
    slyfox
    model IV 1200-flying
    912uls
    IVO medium in-flight
    RV7A-flying
    IO-360
    constant speed prop

  5. #5
    Senior Member Dusty's Avatar
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    Default Re: 912 engine rotation torque

    I believe what is being referred to is the test for check for crankcase fretting. There is a published procedure involving rotating the engine and measuring torque required. A badly fretted case hasn't to my knowledge stopped a 912 but I have seen them go solid on shutdown until they have cooled.

  6. #6
    Senior Member Slyfox's Avatar
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    Default Re: 912 engine rotation torque

    Quote Originally Posted by Dusty View Post
    I believe what is being referred to is the test for check for crankcase fretting. There is a published procedure involving rotating the engine and measuring torque required. A badly fretted case hasn't to my knowledge stopped a 912 but I have seen them go solid on shutdown until they have cooled.
    that's exactly what I was thinking of.
    steve
    slyfox
    model IV 1200-flying
    912uls
    IVO medium in-flight
    RV7A-flying
    IO-360
    constant speed prop

  7. #7
    Senior Member rv9ralph's Avatar
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    Default Re: 912 engine rotation torque

    In the Rotax Maintenance Manual in the Inspection Schedule Item 14 states: "Checking the propeller gear box: Check the friction torque I the free rotation on gearboxes with overload clutch. Actual friction torque________Nm (ion.lbs)"

    on page -5-20-00.

    I hope this helps

  8. #8
    Super Moderator Av8r3400's Avatar
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    Default Re: 912 engine rotation torque

    I don't have it in front of me now, but there is also a test done where a spark plug is removed from each cylinder and the propeller is turned with a scale to measure the amount of torque needed to turn the engine with no compression. This test is for crank bearing clearance and case fretting.

    It is in the manual for 100 hour/annual tests.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
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    Senior Member kmach's Avatar
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    Default Re: 912 engine rotation torque

    You can get the manuals and info free at rotaxowner.com
    Kevin,

    Kitfox Outback
    912 ULS
    Airmaster AP332CTFH-WWR70W
    Summit Aircraft Wheel Skis
    C-FOXW

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