Okay... what could have caused this?

WAG - belt was overtightened causing the damage to the belt. In the process it got flipped around and the rough edges tore into the thin alternator plate.

Also possible, though difficult to imagine, is somehow the alternator was not in alignment with the ring gear to start with. In the pic it almost looks like that tension strap/bar is flexed? May be just an optical illusion.

Also, isn't it unusual to safety wire a tension bolt? I mean, it won't come undone but it seems it could loosen just enough to lose some tension on the belt. I would expect a longer bolt and a property torqued but here.
 
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This guy appears to be safetied backwards:

Screenshot_20250101_225028_Chrome.jpg
Is it still tight?

Screenshot_20250101_225118_Chrome.jpgScreenshot_20250101_225108_Chrome.jpg

That hole doesn't look stripped, but there's no way that screw could've turned out. Guessing it's broken?

Guessing one of those two is the culprit and the rest is collateral damage.
 
That is impact damage on the flange behind the belt v groove. I can't say if something impacted the flange, and ate the belt, or if the belt came off and caused damage to the flange. It appears to me, as you had FOD hit the flange, and may have sucked into the inner side of the belt, and was squished in the v groove of the alt.

I want to ask, was all the bits that came OFF the same exact bits that went ON when the alt was swapped? What about something coming from the interior of the alt, and into the flange? When it comes off, inspect the heck out of it, and see if you can find where there's something missing that is supposed to be there. However, it may have come off in flight, and is gone for good.
 
What's that so called flange doing there in the first place?
 
Ventucky Red said:
Lost the alternator today... luckily it happen close to the home airport where I was able to get back in.. Rebuilt alternator with about 4 hours brand new belt...

Thoughts?

View attachment 136708View attachment 136709View attachment 136710
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Is the alternator seized up?
I put a new belt on a 500 hr alternator and it must have been too tight. Cause after 4 hours it seized up kicked the belt off. Destroyed the belt.

I called Aerotech of Louisville Ky and got a replacement the same day. I took my old one back that came from them in person. With in 5-10 minutes he was showing me the seized bearing. Said the brushes were in good shape at 489 hours since since last overhaul. Really good service company. Didn't charge me for the outer destroyed case. Good people.
3715b008-0a7e-4ac0-ae09-e545d9f677c7.jpg
 
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Ventucky Red said:
Rebuilt alternator with about 4 hours brand new belt...

Thoughts?
Click to expand...
Can't really tell by the pics, but my 1st guess would be the pulley alignment was off and the belt caught the ALT fan plate. Or the fan plate was installed wrong or the wrong plate.

Did the new ALT come with the fan and pulley installed?
 
FORANE said:
What's that so called flange doing there in the first place?
Click to expand...

When I dropped off to be rebuilt, it didn't have one, when I picked up it did... and I didn't question it. I will now..
 
The installation looks normal. The case screws being a bit short in their threads is also normal. And that tensioning bolt is indeed lockwired backward. The "flex" in the tensioning bar is just the normal offset for that model of alternator.

But as other have mentioned, that aluminum plate on the fan is not normal. I have never seen that. There is no reason I know of for it to be there. If the rebuilders used an impact wrench to install the shaft nut, they might have loosened the rotor on the shaft. It is pressed on over splines. It may have shifted and caused some grief inside the alternator and overloaded the belt, which then gets shredded. The pulley may also have worked loose as the aluminum plate crushed and started flapping around.

What was wrong with the alternator in the first place? That might be a clue. A bad voltage regulator can overload the alternator and cause belt failure.

Belt tensioning----there are numbers for that. Most of the time it gets installed and overtightened, and that wrecks the belt, the bearings, the mounting, lots of potential for failure. It's not as if that alternator is absorbing a whole bunch of HP. From a 172 manual:

1735836864197.png

That is far looser than most mechanics will get it when just eyeballing it.
 
Both of my alternators had the plate behind the pulley. I think it has to do with cooling?
I learned the hard way that the belt does not need much tension.


20caa459-2aa0-461d-94e0-957d0aa1ee10.heic
 
Ventucky Red said:
When I dropped off to be rebuilt, it didn't have one, when I picked up it did... and I didn't question it. I will now..
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What part number alternator?
Did the original ALT have that fan plate installed and was left off during removal?


Dan Thomas said:
There is no reason I know of for it to be there.
Click to expand...
I've seen them and was told on some installations its required as a rain/bug shield. But don't know that for sure.
 
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