Stripped Thread for Alternator

Hey Everybody,

First post here. Having a little issue with my old but dang reliable 1984 ford f-150.

I just replaced the alternator as it was going out and the top insert thread attaching the alternator to the engine block seems to be stripped. Tried to get the bolt to thread in for a good hour or so but it wont catch at all. Seems like its damaged right at the front of the insert. For now I’ve put a shorter bolt and nut through it to hold the alternator in place but that’s a poor bandaid fix at best.

I was looking at potential solutions and came across the helicoil or of course I could tap it. The issue with that being the need for space to work. I can’t imagine being able to get the right angle and clearance to pull that off without taking the whole truck apart and putting it on a bench.

I don’t have the time, know-how, or will to do all that.

So all that to say that I was looking at the loctite stripped thread repair kit which seems to have good reviews. My concern is that because the insert isn’t threading at all with the bolt, the kit wouldn’t work because it needs to at least go inside the insert a little bit, right?

Does anyone have experience with that or any other suggestions on how I can go about fixing this? Thanks!

Maybe you could lower the engine to make the location more accessible. I’m not sure how your engine is mounted, and it might only move up. Another possibility is to remove the part or parts that are in the way before installing the insert. Also consider using a TIME-SERT product instead of a helicoil. If you are inserting into an aluminum block, the aluminum, the aluminum helicoil might be better than the steel TIME-SERT.

You may be able to straighten out the damaged threads with a rethreading tap

If that works blue locktite should hold a new bolt once it is snugged up.


There are various options for this kind of repair but (just my personal opinion) is that the Loc Tite thread repair will not hold up.

That alternator mount (like exhaust bolts) is subjected to a lot of what could be called high resonance vibration and the Loc Tite would shake itself apart.
The Loc Tite would probably be fine for something like oil pan and valve cover bolts, intake bolts, etc.

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Agree with Rod and OK. If it is like my GMs the thread is in the alternator so I think you need to clean up the thread or re-tap to a larger bolt. One question though is if the new alternator has the same size hole as the old one. Are you sure the new one is not metric versus the old one? Metric vs SAE can be very close. I broke down and bought a couple of those thread sizers and has come in very handy for determining the size of nuts and bolts and metric vs SAE.


Good idea I had the same problem with the door lock button on my F150 a while back old one was SAE new one was metric.

Thanks for the fasts responses guys. Shouldn’t be an issue of being the wrong size, its not the new alternator that it threads into. It goes through an unthreaded insert in the alternator to thread into the engine block insert, which of course is the same as it was before.

I had not heard of the rethreading kits instead of a tap and die. Seems like that might work. I think its damaged just in the front bit of the insert and I can get a rachet in there without taking anything apart.

I’ll order the specific size (5/8) and see if that does the job. I will report back in a few days when it gets here and I have time to give it a go!

After looking around a bit, not only am I not finding any single 5/8 taps, I am not finding any 5/8 taps in any kits. There are 5/8 dies but not the tap.

Seems to skip over 5/8ths in all of the kits, for example, the one you linked Rod-Knox has a 9/16ths but no 5/8. The other kits I looked at online were similar. Am I missing something here?

Measure the shaft of the bolt, should be 3/8" or 7 /16" .

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I would guess that it was metric but I also guess that @jacob_PNW is thinking that the size of the wrench that turns the bolt is the size of the bolt and of course it’s not.

Yep, Ace is the place but take the bolt down with you to check the size for sure. They have the kit to check hanging on the end cap or if not match a nut up to it.

I always or usually anyway, when starting a bolt, turn it counter-clockwise until I hear or feel the click that it is properly inserted into the thread. Then you know for sure it is not cross threading. Especially on brass or aluminum but others too that can be hard to access, and like spark plugs and head bolts and door knobs and and . . .

The Ace near me has a huge selection of fasteners. You can find a nut of the correct diameter and pitch, then find the tools to match that thread.