Alternator bracket bolt hole in head stripped - what size to tap?

[TheUser]

I have GT40-P heads on the GT and one of the holes for the alt bracket on the front seems to be stripped...which is why the bolt fell out before and caused all this problem w/ the whole bracket falling off, etc that I posted about a few weeks ago.

I bought longer bolts because it seemed to thread once it got in a little ways, but now it only locks at one small point, turn it more and it isn't locked anymore. I don't like this idea one bit, so I definately plan on tapping it. The bolt hole is 3/8-16, and I'm pretty sure I should retap it to 3/8-16, but just for clarrifciation, should I tap it to 3/8-16 or bump it up to 7/16?

 

[nmcgrawj]

Im not anything close to an expert but try the 3/8 first and hopefully that will straighten the threads back out for you. I "messed" up a spark plug hole and just went back over wit with a chaser(same size) and its just as good as new now

 

[TheUser]

alright, Stangnet seems to be pretty much dead right now, but I'll post and hope for some quick replies

Continuing on w/ the previous problem mentioned above, I got the hole tapped out, but the front part of the threads are very loose and the bolt would only hold in the back few threads. Never-the-less, I put it back together - it bolted up ok until I got the belt on there and then it pulled out. It's probably actually better it happened this way instead of going down the road and everything fall off again and I'd have to pull broken bolts out, etc, but I'm still frusterated.

To make a long story short, I guess the tension of the belt is what caused the bolt hole to "widen" in the first place, so I guess I need to make the hole bigger.

My question is...Should I pull the head and have a machine shop tap/heli-coil it to 7/16 or 1/2 or could I do this myself? The craftsman tap & die set I bought last night said it's not for creating new threads, so I suppose maybe I couldn't use it to do this job

I need some advice. If i'm gonna pull the head, I need to do it tonight, so I can get it fixed this week and put back on the car next weekend

BTW, The belt is an 85.4" belt, which seems tight and is kinda hard to get on, but that's what is recommended for a car w/ no smog pump. These belts are expensive ($30-40 each), so I can't afford to be buying all kinds of new belts.

 

[89MustangGX]

Are those the holes that have inserts in them? Maybe you can just unscrew the insert part itself and put a new one in if the threads are still ok on the hole itself?

 

[TheUser]

no inserts. I read the stock heads had inserts or something, but I haven't ever looked at my stock 90 to see. I know my GT-40P's definately don't have inserts.

Anyway, I decided to heli-coil it myself. $20 for the heli-coil kit; $5 for the 25/64" bit to drill the hole. I pulled the fan, shroud, radiator, and unbolted the a/c thing up front and swung it up onto the plastic-covered fender and went to work. I almost got it tapped out to the correct size, but I've been using an 8mm socket to do it and it's slipping now, so I guess i'll go buy the T-Handle (the t-handle I have is too small).

I'll get it finished up next weekend and I think I'm going to use studs to mount the alt bracket this time. I bought some 3/8-16 threaded rod that I'll try to get put in there and just use nuts to hold the alt bracket on. I got the stud idea and the confidence to heli-coil it myself in some of the many threads I read when I searched stangnet for this topic

 

[nmcgrawj]

make sure u get some grade 8 studs.

 

[TheUser]

make sure u get some grade 8 studs.

wow, good catch. I'm not even sure what grade the threaded rod is that I bought. I'll definately have to check that out. Anyone know how to make studs? The pieces are about 6" long and I have two of them. I think they have shorter pieces and that might be better. I'll have to go back to lowes for about the 5-6th time in the past week or so.

 

[gt90stang]

TheUser,

Just Heli-coil it and it will be fine. All Auto stores should have the kit. This happened on my steering pump main stud. The Heli-coil has been working fine for several years now.

Good Luck, Don