Bolt breakage

[Bad Bob]

I wonder why all of the stress seems to be concentrated on that one hole...
Harmonic vibration will, over time, fatigue the strongest metal...
The over-tight belt is a red flag to me.
Having to keep a perfectly dry belt tighter than normal just to eliminate squeal indicates either a bearing going out somewhere (thereby slowing the belt enough to squeal) or an alignment problem (wobbly belts make noise).
Even "new" alternators can come with bad bearings (quality Chinese Steel!) and not all brackets are created equal, either.
You've probably already checked the simple stuff and shimmed whatever needed it...
If all those are copasetic then your total configuration is somehow putting stress in that one spot... and it is time for reinforcements, literally.

 

[Spanky]

OK, here's what I have done: upgraded the stressed bolts to Grade 9 from McMaster-Carr (thanks, Chop) and added a steel strap between the alternator pivot bolt and a bolt holding my fuel pump block-off plate. This seems to have stabilized it a good bit. We'll see . . .

Thanks for all your help guys. All the suggestions were good ones, even though I haven't used them yet. Who knows, I may soon.

 

[choppinczech]

One other thing I always try to do (if possible) is get the shoulder of a bolt into the hole. I've never had a bolt break at the shoulder. Always at the threads. The shoulders of the 5/8" bolts on my revised shock mounts are about an inch deep.

 

[Spanky]

One other thing I always try to do (if possible) is get the shoulder of a bolt into the hole. I've never had a bolt break at the shoulder. Always at the threads. The shoulders of the 5/8" bolts on my revised shock mounts are about an inch deep.

Great idea, but how do you do that when you're using a threaded hole on the engine block? The shoulder won't go in . . .

 

[choppinczech]

Yeah, in this case it might not be possible. You probably can't drill and tap any deeper.

But Aircraft bolts have lots of shoulder and less threads.



NAS BOLTS | Aircraft Spruce

 

[choppinczech]

You'd have to drill out the top 1/2" to 3/4" of the threaded hole to mate with the shoulder.

 

[choppinczech]

The 1/2" bolts on my spring hangers make me nervous.



I plan to make some new 5/8" ones like RESINATOR did.