Sheared alternator shaft

[GJ Humphrey]

The rear alternator shaft in my 1973 T337G sheared.

Fortunately, no metal seems missing that might have gone into the engine, but we're draining the oil and will check the filter carefully.

The ring gear inside the engine accessory case that drives the alternator shaft appears unharmed.

The rotor turns freely and there seems to be no resistance in the bearings.

The coupling (Contitnental type) did not shear , rather the steel shaft sheared. It's a very hefty shaft about .5 inch in diameter. Does anyone know what could cause the shaft to shear and not the rubber coupling? Again, there is no resistance to turning the rotor.

[kevin]

I don't know why, but the same thing happened to my '65 337. And I have heard of others...

Kevin

[GJ Humphrey]

Thanks for the reply, Kevin.

After replacing the alternator whose shaft had sheared, how many hours did you put on the replacement altnerator before selling your ship?

Doesn't this history of sheared shafts argue in favor of using a Lord coupling instead of a Continental coupling? Mine had a Continental. I'd rather replace a Lord coupling from time to time than take a chance on metal from a sheared shaft getting into the engine.

Best,

Gordon

[kevin]

Hmmm.... I may have misled you. It might have been the Continental coupling that sheared for me. I was not paying close attention, we were on vacation at the time, and the shop doing the work (Yingling in Wichita) was not the type that liked people looking over their shoulder. So I never saw the actual broken parts. But I do know the A&P was worried about whether all the pieces could be accounted for, and he had to go into the oil pan to find them all. But he did, so the verdict for the engine was good. Sorry I don't have more specific information.

But, by the way, Yingling did the work at 9PM on Sunday night, and go a new alternator from Cessna by 9AM Monday morning, and had me on my way by noon, so I was just glad it was fixed. This was on our way to the Cayman Caravan, and it was not going to wait for us if we were late.

I flew that airplane another 150 hours on the new alternator before selling it and buying my P337.

As far as a different coupling goes, I have never found the FAA very supportive of creativity in aircraft repair. I am not sure you could get an alternative coupling approved...

Kevin

[Kim Geyer]

We had a shaft shear and figured it was the nut wasn't properly
torqued. You could tell by the wear marks on the shaft.
The mechanic that put it on must have torqued the nut then loosened it to line up the cotter pin hole.
Kim

[skymaster]

73p 60 amp is having lord coupling replaced. coupling cost 250 bucks. also replacing the micro switch on the throttle. Located engine backbone . cost from preferrred 4 bucks. not sure if I should have replaced alternator too. if it works fine .

Monday we closed on the pa31t-1. Cheyene ins was double the 73p337 ins. Its in better mechanical condition than expected. Need 15 hours and ground school. a guy comes out and does it for 2,500 plus expenses. thereafter annual for 1600 plus expenses. 576hg will be available after i get checked out . around end of June .
JCH

[rick bell]

wish i knew about the lord coupl, just paid 1500.00 for just the part, must be getting stupindin my old age

[Guy Paris]

Gordon, I replaced (2) yes two alternators on my front engine... I think it was some what operator induced. The reason I say that is that I wanted both alternators to carry some what equal loads. So I would cycle them off and on. I think that was too much of a shock load on them. Now if I notice the loads not balanced I do NOTHING until on the ground. I further think that I would seriously consider shutting the engine down if alternator failed "IF CONDITIONS WERE FAVORABLE" to determine if shaft was intact. One of the shafts seemed not have a radius at the end of the shafts turning, the end close to the alternator. Yes it was a mess but no metal in the screens (the one at the prop gov.) or the oil filter. The last one I replaced with a new old stock unit. When I questioned the O/H shop about the shafts I was told that they see a lot of sheared shafts. I personally don't think I would buy a O/H unit because of that statement. I am in the process of changing out that front engine now with a factory reman. Hope I get a new alternator with that 26+K engine.. If I don't I will be really pi--ed off. She is at FIT and at Liebfreids. Should be done in a week or so.
guy, the old 72 driver....