Shear Coupling Failure - Ovation 2 Standby Alternator

[29-0363]

Yesterday I tested the Standby Alternator in my Ovation 2 29-0363 (905 hours TTIS) all according to the published procedure, and it failed.  To track  down the fault the top cowl was removed, the prop rotated by hand, and we found the alternator was not rotating, so the problem seems to be the shear coupling.  Have any other readers experienced the shear coupling failure, and at what TTIS?   Was the alternator replaced or overhauled with the shear key replacement?  

It seems that the alternator is essential for TKS equipped Ovations, but not essential for non TKS.  I'm not overly confident flying with the standby U/S because the G1000 equipped Ovation 2 needs plently of power, but then I accumulate some 1000 hrs on my first Ovation 1 (29-0156) in some of the most remote areas of Australia without the luxury of a standby.  

[Jerry 5TJ]

The shear coupling in the standby generator has been upgraded. The manufacturer b&c has the new parts. I installed the upgraded coupling part in 2016.  

Normal alternator  overhaul is recommended at 1700 hours TT  

 

[carusoam]

In case this helps...

Their website...

http://www.bandc.aero/shearcouplings-2.aspx

If you have gone all electric, the B&C alternator takes the place of the primary vac pump...

The two battery system in the O has plenty of power to get you down if the primary Alternator quits...

But if you are in icing conditions in IMC, and far from the next airport.... double up on every system that you can...

PP thoughts only, 

Best regards,

-a-

[buddy]

I replaced the shear coupling on my standby alt. in my O2 a couple of years ago. I replaced it with a vac. Pump shear coupling and I think I payed about $15 for 2 of them.

[29-0363]

Here's the failed Shear Coupling from the Standby Alternator of 29-0363. The reason it stopped working was a very minor oil leak past the accessory case seal to the insides of the Alternator which added rotational resistance.  The oil leak was first flagged during an inspection about 2 weeks earlier, but so slight it didn't drip onto the floor or inside the cowling. 

This item had 900 hours service and looks identical to a vacuum pump coupling, except I'd never seen one with the steel spool on which the coupling is moulded.  The genuine replacement part from B&C is no longer constructed like this - it's simply one complete moulded item (urethane?).   FWIW I would suggest for the relatively low cost of the part, the ease of replacement and the critical nature of a failure especially in hard IFR, it should be replaced at an annual inspection at 5-600 hrs. 

[carusoam]

Great follow-up with pic, 363!

 

Best regards,

-a-