Alternator Bolt Breaks

[Jwtrexler]

This relates to a 1994 ssei. My son replaced his water pump and since then the front altenator bolt ( the shorter bolt that passes through the alternator ear into the bracket) continues to break, almost weekly. I initially tried harden bolts then, most recently, ordered GM bolts . . . still the breakage occurs. It does appear to me the vibration concentrated at that bolt may led to the breeding. There are only two bolts, a long one passing through the rear of the alternator and a shorter one at the front, and there are no alignment or binding issues during installation. Thanks for any advice/ help.

[96 SSEi]

hi, I would remove the alt. and thread the bolts in to the bracket to see if it seats properly - be sure to use the GM bolts and be sure the # on bolt matches the original - I read in my 92 gtp shop manual that the numbers are tensile strength.

you sure the alt seats properly and does not require you to force it to sit?

the bolt was fine before messing with it so I would assume the issue is funky install.

post back pl.......

[Jwtrexler]

@96SSEi
I will do what you are suggesting. I replaced the bolt again (for the 4th time) and it broke again after a couple weeks. The hole in the alternator ear is slightly larger than the bolt, so last time I used a GM bolts plus added a couple wraps of metal tape (used on duct) around the bolt to take up the space; I also replaced the tensioner pulley. I think the bolt is tightening, but will definitely follow your suggestion.

[J Wikoff]

Maybe post a picture of the area. Something amiss my pop out. And video of the alternator while idling.

[scooberu]

If one of the pulleys on your belt is riding on a bent shaft, it will put a pulse load on the on all the other pulleys. Then the weakest mount will break. This happened to me in my first car. It sounds like the shaft on the water pump is slightly bent. Did you put in a used water pump?

It's also possible that your tensioner is not working properly. The tensioner should absorb some of the load. I believe some water pumps also have a tensioner built into them that comes locked; you loosen it as part of the installation. Did yours?

[Jwtrexler]

@Scooberu, the tensioner was replaced last time. Also, I never thought about the water pump shaft being bent.

@J Wikoff, He is getting ready to replace the bolt again and I will get a pic and video.

Thanks to all.

[J Wikoff]

Also make sure the rest of the alternator bracket is properly mounted. Maybe one end is left loose to vibrate?

[MattStrike]

+1 for posting a picture of the area - and also one of how the bolt is breaking so we can see if it's a shear load or tensile load. Sounds really odd that the bolt is breaking and the aluminum is not also breaking or something.

[Jwtrexler]

Pics and videos will be delayed due to the rear bolt breaking when loosing the nut (apparently with little force per my son's feedback); sadly this bolt has been discontinued by GM and I am having difficulty finding a replacement. The diameter of the factory metric bolt is 9.1mm between the head and the final couple mm of thread (I.e., the portion in the bracket and alternator), whereas the diameter of a 3/8 inch alternator bolt is 9.4 mm. Does any have feedback as to whether boring out the "bean shooter type" alternator bracket and alternator bolt hole another 0.3 mm is a bad idea?

It should be noted the alternator belt only goes around the alternator, power steering, harmonic balancer; and new tensioner (not the water pump). I don't think so, but I'll get more involved next time to make sure everything is tight, including bracket mounts. Up to this point, I have many been involved with driller the broken FRONT bolt and using an Ez-Out to extract.

@MattStrike, I will post that also, but I can tell you it is breaking at the "front alternator ear"-to-"threaded bracket" interface.

[Jwtrexler]

Below are two short videos of the alternator after remounting. This time the factory 8mm x 130mm rear bolt was replaced by a slightly larger 3/8 inch diameter bolt; a factory bolt was used to secure the front of the alternator through the ear. Again, the front factory bolt broke in a couple days. I don't see vibration that appears severe enough to cause the bolt to break.

https://youtu.be/BvlDi0FJhB0

https://youtu.be/QDww92IEWIg

[J Wikoff]

There's nothing jumping out at me. Are you getting grade 8 bolts at this point? Stock is probably grade 5.

[michtom]

Have you checked the pulley alignment? Looking at the first video, the alternator looks to be slanted foreword. Maybe optical illusion. At any rate check for alignment.