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Greetings,

I have a 912UL with about 670 hrs on it.  I'm currently preparing for inspection and flight testing on a Sonex Onex.  I ran this engine for maybe 5 hours on another plane before removing it and had no problems other than needing to replace ignition modules.  I was going to reset my pitch on the prop and needed to turn the engine backwards a few inches to get the prop blade horizontal. When I did I was surprised to feel a lot of resistance to turning, along with a really rough feel. Rotating the engine in the forward direction was fine, so after some investigation I decided it had to be the starter.  After removing it, the problem is obvious.  Hard to complain about getting 20 years and 670 hours out of a starter, and I have a new one on the way. Of course I could complain about the price, but that wouldn't get me anywhere :-)

I'm curious if this is a common failure mode.  It was still working, but I have to imagine it didn't have too many more starts left in it.  The shaft and bushing are really trashed, and there's a lot of material stuck to the magnets.  I have to imagine most of that is bits of magnet that was scraped off?  Again, just curious mostly.

Cheers,

Rusty 

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9020_1_bad starter 0003.jpg (You do not have access to download this file.)
9020_1_bad starter 0005.jpg (You do not have access to download this file.)
9020_1_bad starter 0006.jpg (You do not have access to download this file.)
  • Re: starter failure

    by » 5 months ago


    What I see is an Old and Worn starter.
    The rotor and stator show fresh metal so they have been contacting each other.
    Probably due to the bearings getting sloppy.
    - - -

    Turning the Prop in reverse a few inches did not have anything to do with this issue.
    When you turn the prop in reverse, the Sprag clutch engages Immediately and rotates the Freewheel Gear and the Intermediate/Idler Gear and Starter, which are ALWAYS engaged.

    The gearing from the prop to the starter is about 72:1, so a small amount of prop motion produces a large rotation at the starter.
    The resistance you felt was from back-driving a 72:1 geartrain and the Rough "Feel" was the carbon brushes in the starter sliding on the Commutator.

    All of this is normal and to be expected.
    Turning the prop in reverse causes negligible harm, but should definitely be kept to a minimum.
    A few inches of reverse rotation is acceptable, just don't go doing full prop revolutions in reverse.
    You will shorten the life of the Starter brushes

    This subject always generates diverging opinions.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


    Thank you said by: James N Parker

  • Re: starter failure

    by » 5 months ago


    Thanks for the confirmation. It kinda looked like an old worn starter to me as well.  I'm sort of surprised at the damage to the shaft and bushing, but I guess it's not oiled in any way, so I shouldn't be too surprised.  Seems like a good place for a bearing rather than a bushing.   

    For the record, I knew turning the prop backwards a few inches didn't cause the problem.  I only mentioned it as how I discovered the problem.  I have another 912UL on a test stand, and immediately compared it to this engine.  As expected, it was night and day.  It took some research to see why it was bad in reverse, but once I understood the sprag clutch arrangement it made sense. 

    I had never realized the starter motor turned that much in reverse rotation, so it does make another good reason not to turn it backwards any more than necessary. 

    Cheers,

    Rusty


  • Re: starter failure

    by » 5 months ago


    Yep that starter looks like it's been around the block a few times. At 20 years old plus being the old black starter it's time to replace it. You will like the gold colored higher torque starter much better.


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


  • Re: starter failure

    by » 5 months ago


    I'm glad you mentioned the gold heavy duty starter (685974).  I had assumed that was for the high compression engines, so I ordered the more expensive black starter (889751).  Looking at the Lockwood page again, it does list 912UL as one of the engines the new starter can be used on.  Lockwood hasn't had a chance to ship yet, so I've already send them an email, and will call first thing Monday to change the order. 

    Thanks,

    Rusty

     


  • Re: starter failure

    by » 5 months ago


    RUSSELL A DUFFY wrote:

    I'm glad you mentioned the gold heavy duty starter (685974).  I had assumed that was for the high compression engines, so I ordered the more expensive black starter (889751).  Looking at the Lockwood page again, it does list 912UL as one of the engines the new starter can be used on.  Lockwood hasn't had a chance to ship yet, so I've already send them an email, and will call first thing Monday to change the order. 

    Thanks,

    Rusty

    They don't use the older black starter anymore. They'll send you a gold one.


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


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