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Hello all,

I am getting ready to install a rebuilt gearbox on the 912 ULS on my experimental aircraft and am unsure about the proper torque for the crankshaft nut.  I had read section 72-10-00 of the Maintenance Manual Heavy for the 912/914 Series Edition 2 / September 2022 to gather information about torque, loctite usage and so forth.  On page 5 of 71-10-00 there is a diagram showing torque and loctite usage on an exploded view of the gearbox.  The torque value shown there for the crankshaft nut is 300 Nm / 221 Ft Lb so that is what I was planning on using.

I watched the site video on removing and installing the gearbox to make sure I understood each step of the process and noticed that the video called for a torque of 150 Ft Lb for the crankshaft nut.  Rodger Lee also quoted a 150 Ft Lb value in a thread about a year ago.  That thread was later than the September 2022 MMH publication so I thought maybe I had old information but, as far as I can find that is the latest MMH. 

I did find a value of 200 NM / 147 Ft Lb in the Maintenance Manual Line for the 912 series edition 4 / July 01, 2021 page 5 section 05-50-00.  That is likely where the 150 Ft Lb value came from.

So, I have two Rotax manuals that seem to show different values.  Which one should I use?

Thanks!

  • Re: 912 ULS Crankshaft Nut Torque Question

    by » one month ago


    Hello Todd

    The protocol is to use the newest manual for updated data.  The latest release shows 300 NM and Loctite.

    Cheers

    38996_2_crank nut value.jpg (You do not have access to download this file.)
    38996_2_TOA heavy 912 latest.jpg (You do not have access to download this file.)
    38996_2_web info hmm 912 .jpg (You do not have access to download this file.)

    Thank you said by: Todd Bailey

  • Re: 912 ULS Crankshaft Nut Torque Question

    by » one month ago


    Thank you Wizard.

    Using the latest value was my inclination but I just wanted to be sure that I wasn't missing something as the difference in the values was so large.   The site might want to add a note to the gearbox removal - installation video that the torque value has changed.

    Thanks again for the quick reply.


  • Re: 912 ULS Crankshaft Nut Torque Question

    by » one month ago


    Hi RW,

    A couple of questions.

    What was wrong with the 150 ft/lbs? Did Rotax have some nuts come loose? I haven't heard of any coming loose using 150 ft/lbs and Loctite 648 green sleeve retainer. Rotax used this torque setting for many years. What made them change?  Most people don't have the ability to get to 221 ft/lbs. 

    Is there any chance of bending the crankcase locking pin?

    Since I'm one of these science based analytical types I'm just curious about the inner workings here.


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


    Thank you said by: Sean Griffin

  • Re: 912 ULS Crankshaft Nut Torque Question

    by » one month ago


     

    "What was wrong with the 150 ft/lbs? Did Rotax have some nuts come loose?"

    Roger, the answer is yes.  i actually think some were never installed correctly in the first place.  That said the value for the size and thread is at the top end for that part and personally have not had an issue installing one to the new torque.  The locking pin works fine.  

    Cheers


    Thank you said by: Sean Griffin

  • Re: 912 ULS Crankshaft Nut Torque Question

    by » one month ago


    If the 300nm / 221 ft lbs is beyond the limits of ones torque wrench, how about using a torque extension and the math to calculate it out?

    Two purposes, A) it is going to be like using a cheater pipe and B) a calibrated torque wrench (ratchet) is most accurate in its mid range so if a 'technician' is using a 200 ft lb 1/2" torque ratchet at max range and then just going a 'little more' it really is just a guess.

    At very least I suppose they know they likely got at least 190+

    I would only use the Rotax P/N locking pin for this and not an improvised grade 8 bolt imitation... A good many of us are builders and therefore 'makers'. My first locking pin for testing the gearbox clutch was just that. 

    [My kids never realized that shampoo and toothpaste came in HUGE size containers until they went off to college...]


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