I hadn't started my Duster in a few weeks so I went out in the garage today to do so. I started it up and suddenly heard a strange noise I never heard before. It was kind of a whirring/buzzing sound when I revved the motor. When it returned to idle speed the sound stopped. Did this a couple of times so I shut it off and looked under the hood. To my surprise this is what I found. Wasn't like that before so I don't know what happened. The motor is just a stock 318.

How did you tighten the belt the last time?

Yea, It looks like it was probably pryed on when tightening ( maybe not by you but maybe PO)and the crack started. Then over time the crack got larger.

Another possibility is the thickness or stackup of the spacers are incorrect and basically when it was tightened down it wanted to try and pull the ears of the alternator together.

Why is everything silver?

because... its Purdy like that.. ... I wonder if it effects the alternator output or not?

It appears that the belt/pulley is out of alignment? That and some metal fatigue from prying on it to adjust it probably did it in.

I was wondering if it was affected by it too.
As for the belt alignment, a laser bore sight tool laid in the pulley groove will self center in that pulley and you can check alignment with it very accurately.

If the rear mounting ear breaks then yes, it throws the pulley out of alignment.

It would have to be set back up with an intact alternator to know if the alignment was off before this happened.

Thats a new one to me.
When you take it off, examine the fracture.
At minimum you will see if the any or all of the fracture is fresh or old. Heck. Someone could have dropped it on a concrete floor and started a fracture then.

I'm betting the belt alignment was off causing the case to break. In the one picture, that belt is coming at a pretty hard angle towards the alt pulley. Even with the case broken, the outer edge of the pulley still isn't in line with the belt. It looks like the alt would have needed an outer pulley to be inline with the water pump pulley.

It looks like maybe the front ear of the alt needs sit outside of the bracket coming from the water pump, then you might need a different rear spacer. You may have incorrect brackets. Gene

Yep seen this many a time.

^^^ X3

Yes look how far the rear sliding section is pushed in....

The alternator bracket should be sandwiched with the long spacer in between the two ears not out in the front. Here is a link to a pic of a small block setup.


https://www.forbbodiesonly.com/moparforum/attachments/altstock-jpg.12272/

that inner "split" sleeve needs to be protruding a bit behind the rear ear (cant see in the pic) & the right length long spacer "inbetween" the ears with just the right length (add washers if needed) so the ears ain't being pressed "inward" & the inner split sleeve(s) are taking the compression. EDIT I looked at the pic again & the rear split sleeve might need to pressed rear ward a bit (so some of it protrudes rearward from the rear ear), "as/if needed" cuz some needs to be protruding, then slightly shorten the rear spacer to maintain the alt/pulley alignment.

Also .. when you get a new one ... get one with the stator not painted / coated with that paint. not sure but you could be creating more heat as well thus in the long run weakening your metal case... get one that has that nice shiny copper with no paint...

saw that a lot in my days as a junkyard owner. two causes for that to happen, both previously mentioned. using a big prybar to set belt tension, and mixing up, or not using the correct spacers. happened on all brands, so not mopar specific.

As mentioned earlier, looks like the upper alternator bracket is not positioned properly. The bracket should be between the outer alternator ear and the spacer. The split sleeve is pushed forward because the bracket isn't in the right place.