One or two of my crossmember bolt holes are stripped. I noticed the first time I took the crossmember out bubba had been there before because the bolts themselves seemed to have little thread on them. These are the four tapered bolts( 2 on each side ) that bolt up directly into the frame. I swapped one of these bolts for a normal bolt the same size and it just spins in the hole now.

Is there any way to fix the threads inside the holes in the frame ?

 

Seeing that your vette is so nice, you will need to helicoil that.
Otherwise, you could just drill and tap the weld nut for the next size up - 7/16 - and open the crossmember hole.

A regular 3/8-16 bolt works fine ... what I currently use.

 

A helicoil isn't a bad deal either, but you are dealing with a captive (welded) nut arrangement, so you don't have a lot of stable material to work with.

Another, somewhat more difficult, option is to drill the whole thing out and weld in a new captive nut of the standard size. This, of course, would be much easier with the crossmember removed (to do it from the back or upper side.) Come to think of it, I'm not sure there is not an access hole of some sort on the top. If you do weld in another nut, avoid the temptation to weld in a Grade 8 - the weld heat will ruin the tempering and only make the new nut weak - a long (or multiple nuts lined-up on a sacrificial bolt of Grade 3 (or less)) is the best approach. If you do that and use a sacrificial bolt put some antiseize or at least thick carbon coating on the bolt before you put it on or you will leave the bolt in there!

I have one nuked on both sides of mine and did nothing to them. Bolts sort of stay there anyhow, but don't tighten. On one of them I slathered some epoxy on the bolt when I ran it in and it stopped the rattling (surprise! surprise!)

I do wish I had remembered to fix the stupid thing when I had the xmember and pipes off during the engine change (mine are continuously welded and so "permanently" through the member.) Somebody REMIND me to when I pull the pipes and member off to have more room when I change gas tanks in the next month or so!!!

Someone with more expertise into structural mechanics could confirm, but to me these two vertical bolts are not critical for strength as the main horizontal one is. I believe they are mainly there for positioning concerns and to prevent rattles, as the design for the removable crossmembers relies less on bolt strength at all than the big flange and blocking beam of the crossmember itself. (I also can't think anything too critical would have been left to an inferior fixed nut arrangement in the first place, when a removable nut with an access hole would have worked as easily.)

 

this was my observation also....we just tapped and put in a larger bolt when ours did the same thing...

 

I would use a hole saw slightly bigger than the captive nut is (just guess) and saw out the captive nut, then remove the captive nut from the sawed out piece, weld a new on on and then weld the section back in, grind smooth and it'll be an almost invisible repair

 

I took down the cross member and welded inside four 5/16 X 5" long plats. Then drilled and taped eight 1/2" holes and bolted it back in.

 

Thanks guys I might try the one size bigger drill and tap trick or maybe the helicoil first, I have never done a helicoil, is it hard to do and I thought it was for aluminum, it will work on steel ?

TT you probably have the right idea but that would require some welding skill

 

what a great opportunity to buy new tools ( a welder)

 

I have one but lack the skill

 

I have one but lack the skill, welded a hole in my brother's motorcylcle oil tank, then he had the nerve to come back and ask me to weld somethng else. He dropped that on the floor and it broke at the weld, he hasn't been back since

 

LOL, just practise a little, since you're using a hole saw you can't put it back in the wrong place. Just saw it out, weld on a new nut. Then use a little strip larger than the round sawed out section and a bolt to keep the 2 together, that way you can't push the section into the frame and loose it, or weld it in crooked. Just chamfer the side of the sawed out section and the frame and set the welder to a high setting and start tacking it to the frame w/ a couple of tacks (4 should do it) and then final weld it, and grind smooth. It takes a lot of heat to put a hole in the frame, sure setting the wire speed really high and the voltage also will do it (but you'll get nice dripping molten droplets first and the second you get one of those on your hadsnyou'll stop welding..guaranteed ) but when using common sense you won't go through the frame. Also, that bolt does not carry the load, the through bolt on the inside of the frame does, the 2 smaller ones are for locating the crossmember.

 

I would just tap it rather than installing a helicoil. You'll have to open it up and use the helicoil tap in there anyway, so might as well just go with a bigger thread and not mess with the helicoil.

I don't know how a helicoil would work going straight through a nut. I would think they are designed to bottom out in the hole.

 

That is what I thought at first but I think there is some load on those bolts, if you look at the crossmember you can see it is welded in kinda two pieces going straight down the center on both sides and it looks like the bolts are there to help those welds, kinda hard to explain unless you are looking at it but if those welds start to give the bottom two bolts will support the crossmember if the bolts were not there the crossmember would split.

 

I know what the crossmember looks like It's 2 u channels welded together. I don't think the bolts are there to keep the crossmember from falling apart (although it does sport the usual gm welding skills), without the 2 bolts on the bottom the crossmember can move a little and rattle on the through bols, the 2 smaller bolts on each side are there jsut to keep it snug in place...I think

 

So, it sounds like going a size larger is not a big deal for you - easy.
Better yet, do all four and call it Heavy Duty.