starter failure

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.
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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.

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

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.

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

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.