SBY ALT shear coupling - failure and replacement

[EarthboundMisfit]

Second failed shear coupling on Ovation2 GX 29-0363.  First failure was at 950 TTIS, latest at 1450 TTIS. 

No charging of BATs when on EMERG BUS at 2000+ RPM:

Confirmed with no visible rotation of SBY ALT when manually turning propeller (IO-550-G(7)B with B&C Specialty Products standby alternator):

This is what a failed shear coupling looks like:

And the new (style of) coupling which seems beefier than the old one:

Correct operation (+ve AMPS/charge) on EMERG BUS:

[carusoam]

Great details EbM!

Was their any hunt required for the extra materials released by the shear coupling?

Some shear couplings are internal to the engine… and may require an oil change or some method of finding the bits and pieces…

PP question only, no knowledge of the B&M alternator implied…

Best regards,

-a-

[N201MKTurbo]

Shear couplings never fail, they just do their job.

[LANCECASPER]

7 hours ago, N201MKTurbo said:

Shear couplings never fail, they just do their job.

Exactly . .  they are doing what they are designed to do.

[EarthboundMisfit]

This might be semantics.  I agree the coupling is designed to break.  However, when it breaks, that's the failure mode to me.  Couplings DO fail. 

[N201MKTurbo]

1 hour ago, EarthboundMisfit said:

This might be semantics.  I agree the coupling is designed to break.  However, when it breaks, that's the failure mode to me.  Couplings DO fail. 

But why did it shear the coupling? That is the failure, not the coupling.