Diehl Accessory Case/Slick 4316 Magneto Drive Hub Damage

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N804RV

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Started annual inspection on 4SP and pulled the magneto to comply with Slick service bulletin.

Found damage to both the spacer and the drive hub mounted to the Alternator rotor/flywheel. This install has no starter or full size flywheel with starter ring. It just uses the flange that takes the place of the flywheel on the Sonerai-Great Plains X-Casting.

Since the lugs on the drive hub are perpendicular to the lugs on the magneto drive gear when the spacer is properly installed, I can't figure out how the thing could go together and the spacer not be centered (concentric). But, looking at the wear on the outside circumference and the other damage, that seems to be exactly what happened. It looks like it eventually seated and found a position it liked. Because the engine had run flawlessly for 2 years and 180 hours.

I bought this aircraft in flying condition. The only reason I pulled the mag was to do the service bulletin.

1. Has anyone else ever seen this kind of damage?

2. What to you do to insure the phenolic spacer stays in position when you install the magneto?


This is what I found:



 
Last edited:

TFF

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Solution, I don’t know except keep an eye on it. It’s just a wear item. Time control item in certified world. At least the material is not going to fall apart. Lycoming uses rubber bushings to engage with those drives.
 

Dan Thomas

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180 hours is almost nothing in the certified world. That shouldn't be happening.

Hard to tell, but it looks to me like the drive on the crankshaft isn't centered on the crank. That would cause this problem.
 

BoKu

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...Hard to tell, but it looks to me like the drive on the crankshaft isn't centered on the crank. That would cause this problem.
Good thinking. I'd recommend putting a dial indicator on the case extension and checking to see if the drive lug is centered. Then I'd put the indicator on the crank and see if the hole in the case extension is centered on the crank axis. It could be that tolerance stack-up between those two things is more than the adapter can accommodate.
 

Pops

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Also sort of looks like the tangs were not fully engaged in the grove of the puck. Need to measure how far it is engaged ( with the crankshaft to the rear of the endplay).
I agree on the first thing would be to check to make sure the case extension is centered on the crank axis.

On my conditional inspection, I always take the mag off and inspect the puck for any wear .
 

Mcmark

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Sep 24, 2013
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Is this the unit that pics were shown in another topic recently all mounted up? It was a picture, so there is parallax and such, but the alignment on that looked questionable.
 

don january

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I couldn't help but to envision compression kickback on shut down causing the puck to be slammed by crank.
 

N804RV

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...Hard to tell, but it looks to me like the drive on the crankshaft isn't centered on the crank....
If that were the case, I think I'd know. I would think the airplane would vibrate like an unbalanced washing machine stuck on the spin cycle.

Relatively speaking, that is a lot of moving mass hanging off the end of that crank, theres the crank flange adapter that takes the place of the flywheel and mounts behind the gland nut, the magneto drive hub, and the rotor for the alternator (heavy). Also, that alternator stator doesn't show any uneven wear.

I have a theory on how it happened. All I can say is I'm glad I pulled the magneto. And, I'll be pulling it on every annual from now on.
 
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