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My 2016 Rotax 914 UL has been running for 198 hours. All maintenance has been done and used the Rotax oil. Yesterday I did the friction torque measurement. The value was within specification ( 367 inch/lbf).

After dismantling the gearbox , I also performed the torsion and crankshaft distortion inspection. The crankshaft was within specification.( - 0,6 degree for cilinder 4)

But the following I found. Turning the crankshaft ( cold engine, no spark plugs fitted) I needed 260 to 370 inches/lbf to overcome the first initial

drag, then immediately the torque was 27-57 inch/lbf during turning the crankshaft.

After 20 minutes waiting I had the first resistance again and that disappeared immediately after turning.  The engine runs perfect. and has no problems with starting , also not when  starting the hot engine direct after a long flight. I have no oil leakage .

Ir this normal or as some people told me this can be an indication of a starting crankcase fretting process and do not use the engine anymore before an overhaul. 

Please advice.

  • Re: 914 crankshaft turning resistance during first 10 degrees

    by » one month ago


    They were using thru bolts by 2016 so fretting shouldn’t be an issue.


  • Re: 914 crankshaft turning resistance during first 10 degrees

    by » one month ago


    Sam is correct, fretting crankcases were on the older engines (2006) and mostly found with the 912ULS (100hp). 

     

    If you go to the Rotax 914 line maintenance manual located here - https://www.rotax-owner.com/pdf/MML_914_Series_ED2_R2_E.pdf

    Section 05-50-00 subsection 3.9 (Hard to turn over) page 20 provides a specification. The check must be done with the gearbox installed.

    “Torque must be determined with a suitable jig. To do this, determine the maximum occurring torque on the propeller shaft necessary to move the whole crank drive. The torque must be max. 150 Nm (110.64 ft.lb)”

    When replacing the crankshaft during overhaul, the crankshaft is rotated to make sure that it rotates freely; however, there is no specification or torque number recorded during this check therefore you must complete this inspection using the above instructions found in the line maintenance manual Section 05-50-00 subsection 3.9 (Hard to turn over) page 20. 

     

    We have seen some (very few) engines have a “tight” spot when rotating, and that was due to a build-up of lead that fell off the piston dome and took up clearance between the piston and cylinder head. We have only seen this on a couple of engines that operated 100LL for hundreds of hours and without frequent oil changes. 

    What type of fuel are you using?


  • Re: 914 crankshaft turning resistance during first 10 degrees

    by » one month ago


    Thank you foor the response. I mounted the gearbox  and burb  the engine. Left the engine for 24 hours and today I did the tests as described line maintenance section 05-50-00 section 3.9

    I found the following values. Start I measured 37,2 ft/lb. Slowly moving around (360 degree) I found  two tight spots and needed friction torque 41,4 and 75 ft/lb rotate through

    Overall the rotation friction torque through was 20 - 12 ft/lb  over the 360 degree rotation.

    I checked the tight spots. Stopped just before the resistance and wait 10 to 20 seconds. The more a waited the more torque I needed to pass the point.  I found values 109 and 66 ft/lb. Rotating continued  over the 360 degree there was no real tight spots anymore observable.

    I tested the free movement ( 30 degree ) of the Gearbox and made sure  the crankshaft was fixed.  The torque was 84 - 109 ft/lb

    Rotation the gearbox it makes sometimes a "dry" rasping sound. ( like it is dry inside on a bearing or ring)

    I use fuel Super plus without ethanol  98 octane

    include some pictures of the dog gear and dog hub.

     

     

     

    32656_2_Pitting dog gear .jpg (You do not have access to download this file.)
    32656_2_Dog plate.jpg (You do not have access to download this file.)
    32656_2_Dog hub 2.jpg (You do not have access to download this file.)

  • Re: 914 crankshaft turning resistance during first 10 degrees

    by » one month ago


    From the pictures I thinks it's time that gearbox was sent in and get overhauled.


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


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