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M20K Rebuilt Alternator bad already?


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Just got my M20K out of annual 3 weeks ago (out of state, can't go back to their shop).  The alternator (ALX-9525B) and drive coupling assembly were replaced.  On Sunday afternoon on a flight home, voltage drops from 13.6 to 12V.

Reset the breakers and the master inflight to no avail.  An experienced, local A&P tells me the alternator is bad.  It is under warranty but Hartzell wants the alternator pulled and shipped back to them before they will replace it.  Has anyone else had an rebuilt alternator fail in less than 20 flight hours?  

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8 minutes ago, LANCECASPER said:

Not a good idea to reset the breakers in flight.

 

 

He never said a breaker popped, just that he reset them. Big difference between manually pulling a breaker out to reset it and pushing one in that has popped out due to a short/electrical issue. 

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Right.  The circuit breaker did not pop.  I received a High/Low volt light flashing, voltage dropped to 12.0 and AMP meter indicated discharge.

I referred to the POH in flight and followed the 'Electrical Alternator Failure' and 'Alternator Low Voltage' emergency procedures. Both procedures include pulling the Alternator Field circuit breaker. 

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4 hours ago, Trex20105 said:

  Has anyone else had an rebuilt alternator fail in less than 20 flight hours?  

Yes, I've seen that happen- but not nearly so often as the other things mentioned above-

1.) broken field wire (or it fell off because it wasn't tightened)

2.) bad voltage regulator

3.) bad alternator

Please let us know which it is, and good luck.

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Located source of the problem.  Had an A&P pull the alternator this morning and found that the drive gear assembly was separated from the alternator.  Not sure if the cotter pin on the nut  failed or was not installed properly.  The threads are flattened so the alternator needs to be replaced.

IMG_0298.JPG

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1 hour ago, Andy95W said:

At least Hartzell should be on the hook to replace it.  Glad you got it firgured out!

I doubt it - the alternators come without gears, its your mechanics responsibility to remove and refit - not the first time a mechanic has forgotten to put a nut on, or a cotter pin in.  I'd document this really well, and look for that nut and cotter pin?  I'd be telling the previous shop what has been found, give them the chance to assist.  I'd also advise my insurers - this could get expensive.  If there is a nut floating around in the engine, damage has already been done.

You don't have to follow through with a claim, but adjustors are good at working out who's responsibility is what,  Don

 

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  • 3 months later...

Sorry for the late follow up on this.  The nut was located, laying just inside the alternator mount location.  No sign of the cotter pin though.  The A&P suspects the cotter pin was not installed.  The oil and filter were changed.  Have flown about 25 hours since and so far, so good.  Almost time for another oil change and will have analysis done.  The shop that installed the alternator did send me a replacement at no charge.  I am still out of pocket for the local A&P charges though. 

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Over on Beechtalk this alternator has become a repetitive inspection item. So many of them have the cotter pin improperly installed or the coupling disintegrates but often the result is a chewed up alternator drive gear and a new engine. I would raise some hell with the installing shop, they should check the alternator to be sure it conforms before bolting it on, and that includes VERIFYING the cotter pin is installed. They coud have killed somebody, the least they can do is cover your charge to fix their mistake. Also, share the final disposition of this and the shop so we can be better informed.

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Well, I am going to take a guess.  There is a bushing that is supposed to be installed inside the coupler, it is between the coupler and the shaft for part of the length of the coupler.  If the bushing is omitted, the coupler wobbles.  The cotter pin that goes in the end of the shaft is tiny.  The wobble beats the cotter pin up and everything comes off.  Non-Mooney mechanics who have not worked with that coupler before and don't look at the repair manual, will make that mistake.

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On 8/4/2017 at 1:10 PM, carusoam said:

Great pic, thanks for sharing.

Did the nut and cotter pin dissapear inside the engine?   Ugh!

Best regards,

-a-

Yup.  The oil has to be drained and all those pieces accounted for.  The cotter pin is tiny as I said, and you will find it in pieces.  Don't ask me how I know.

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9 hours ago, jlunseth said:

Well, I am going to take a guess.  There is a bushing that is supposed to be installed inside the coupler, it is between the coupler and the shaft for part of the length of the coupler.  If the bushing is omitted, the coupler wobbles.  The cotter pin that goes in the end of the shaft is tiny.  The wobble beats the cotter pin up and everything comes off.  Non-Mooney mechanics who have not worked with that coupler before and don't look at the repair manual, will make that mistake.

There are other factors at play as well.  Many procedures aren’t in the Mooney manual, but are in the engine manual or in engine service bulletins which require further digging and research.  In the relentless CB push for cheaper prices, work is being done by mobil mechanics or small shop who don’t charge enough to own a maintenance library.

Clarence

 

Edited by M20Doc
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This is one of the reasons I have all my maintenance done at the MSC at Willmar.  Everything.  Unless there is something that needs attention on the road.  I have just run into a succession of these types of small but deadly mistakes at non-MSCs over the years, its not worth it.  Not that my MSC is perfect, but they have a talent for not making the mistakes that can kill you.  It sounds like this mistake is more common than I had thought.  Maybe we should have some kind of section for permanently pasting up common, serious problems.  I am on a sailboat forum where they have such a thing, and it has been great, let me catch and fix stuff I never would have thought of before the alternator falls off, takes the belt with it, and the engine is damaged.

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2 hours ago, Tommy said:

Pardon my ignorance. Is this something that can be inspected easily (cowls off and a good torch)? If so, can someone share a photo of where this bit sits?

Thanks! 

Continental engines use a very different alternator setup than our Lycomings.  They are gear driven from inside the engine, ours are externally belt driven.

Also, please don't take a torch to your engine.  There are better ways to inspect components. :rolleyes:

(American readers will get that.  You and Andrew Hyett might not. :P

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10 hours ago, Andy95W said:

Continental engines use a very different alternator setup than our Lycomings.  They are gear driven from inside the engine, ours are externally belt driven.

Also, please don't take a torch to your engine.  There are better ways to inspect components. :rolleyes:

(American readers will get that.  You and Andrew Hyett might not. :P

Learning new things every day! Sounds like a "well it seemed like a good idea at the time" sort of design. 

Time for a cup of tea and some crumbles for us who fly a Lycoming! 

Earl "grey" anyone? ;)

 

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The presence or absence of the coupler bushing is invisible when the alternator is assembled, esp. onto the engine.  The only way to find the fault is to fly the plane until the wobble beats the cotter pin to death, and the pin pieces, the nut, and the coupler itself fall off into the engine.  Then you will know.  Either that, or dissassemble the whole thing to look at it, and then of course the person doing the dissassembly for inspection can make the mistake when putting it back together.  In other words, if the shop has an apprentice do the job and an IA then inspects it, he will never see the problem.  Again, don't ask how I know.

Edited by jlunseth
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