'63 Valiant V200 wagon - rare bolt issue

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shortmort37

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I'm finally getting around to installing my tailgate torsion bar, which I had reproduced to match the shape of a rusty one supplied by @65 Dartman, and tempered to the correct hardness. Inside my tailgate, there were three clamps; the one on the drivers side is bigger and heavier, or course, because it holds down the bent end of the bar, and sees all the action. There were only fragments of the original torsion bar. The middle clamp was lying inside the tailgate, with the bolt missing; the clamp at the other end was still bolted in place. I managed to get the old bolt out, although it was badly rusted; I cleaned it up pretty well with a 1/4-20 die, and now it turns freely, as it does with a 1/4-20 nut.

I got some 1/4-20 bolts of the right length, and attempted to put them in. They don't fit! They start, but - I bent one trying, and snapped the head off another. Fortunately I was able to back it out, and the old bolt still turns in the holes.

I'm persuaded at this point that the old bolt is not 1/4-20 - it's a #12 bolt, or a 12-20. They are rare today, but apparently once used in some applications - and I think this is one of them. A #12 bolt has a 7/32" shank, or 1/32" less than that of a 1/4" bolt. 1/32" is probably enough to account for the trouble I am having.

If I had easy access - or, enough room - I'd tap one of the holes (since the old bolt is serviceable) to 1/4-20. But I don't.

Is my supposition plausible? If so, where do I go to get a 12-20 bolt?

Dan

bolts.jpg
 
Did you try Ace hardware
 
69FBCuda said:
Did you try Ace hardware
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Ace Hardware is where I bought the 1/4-20 bolts, on the assumption they were correct! I didn't see any 12-20, although admittedly I didn't look - but I don't recall seeing that as an option when I searched the aisle. You can't buy them on Amazon (I've looked), and a general search doesn't provide a supplier. That may just mean I haven't searched in the right place, but I'm striking out so far.
 
Sounds like it is time to measure what the old bolt really is. Calipers for the O.D. and then count the threads per inch (or use a thread pitch gauge), or just take a 1/4-20 bolt and nest the threads together side by side. If the threads nest perfectly then it is a 20 tpi pitch.
From what you say you ran a 1/4-20 tap in the hole and it worked but a bolt won't work? Something else is going on there.
A #12 screw is .216" dia.
Worst case is you use a proper size tap drill for 1/4-20, then retap the hole. That should convert the hole.
 
Get a proper cutting tap and tap it to 1/4 x 20 and go.
 
@shortmort37, I agree with @RustyRatRod, tap the hole. You said you didn't have room, can you provide a picture? Now I have NOT seen it yet, but it seems that if you can get the bolt and a wrench in the correct area, you should be able to get a tap in there. If the area is like inside the tailgate and there is no room to use a standard 1/4 x 20 tap, then try to find a short/stubby tap or make one. If necessary, I see no reason why you couldn't cut a regular tap shorter and grind a square top on it like on the top of a regular tap. That is what I would do.
 
D/Dart man said:
Sounds like it is time to measure what the old bolt really is. Calipers for the O.D. and then count the threads per inch (or use a thread pitch gauge), or just take a 1/4-20 bolt and nest the threads together side by side. If the threads nest perfectly then it is a 20 tpi pitch.
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Yeah, the old and new in the pic above nest perfectly; and a 1/4-20 nut spins freely on the old bolt.
From what you say you ran a 1/4-20 tap in the hole and it worked but a bolt won't work? Something else is going on there.
A #12 screw is .216" dia.
Worst case is you use a proper size tap drill for 1/4-20, then retap the hole. That should convert the hole.
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I can't get the 1/4-20 tap to start in the hole. Certainly no room to drill inside the tailgate - but more about that in a comment I will make further below.
 
harrisonm said:
@shortmort37, I agree with @RustyRatRod, tap the hole. You said you didn't have room, can you provide a picture? Now I have NOT seen it yet, but it seems that if you can get the bolt and a wrench in the correct area, you should be able to get a tap in there. If the area is like inside the tailgate and there is no room to use a standard 1/4 x 20 tap, then try to find a short/stubby tap or make one. If necessary, I see no reason why you couldn't cut a regular tap shorter and grind a square top on it like on the top of a regular tap. That is what I would do.
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I can get my 1/4-20 tap in there, but not with the handle to turn it. Although I could turn it with a crescent, the tap doesn't want to start, and I'm not going to be able to apply the pressure to get it started. But I have a plan B...

On the driver's side, the bolt was so badly rusted that even after continuous soaking with penetrating spray, I managed to snap the head off. No room to drill it out from the inside of the tailgate; so I measured carefully, and drilled it out from the *outside* of the tailgate (inside the cargo space). I then tapped it, and with a bolt that's longer than the old, it will come through the tailgate panel - I'll cut it flush to plug the hole. I can do the same, on the passenger's side.

Like I say, plan B. But I know this old bolt - of which I need two, because there are three clamps - is not 1/4-20. I know that, because I bent one 1/4-20 and snapped another trying to get it in either of the two remaining holes. This is def a 7/32-20 bolt (#12-20), frequently used in motorcycles in the old days from what I read. As to why it was used here, only heaven knows.
 
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are you using a tapered 1/4 20 tap or a bottoming tap? By the looks of the pictures of the original bolt you posted if you can't get a tapered 1/4 20 tap in there and turn it with a 4 inch crescent wrench you can't be holding your mouth right. I've been there myself. Take a step back and put a tapered tap in there, make sure it is straight level square plumb with plenty of lube and turn it slowly with your small crescent.
 
jeff alder said:
are you using a tapered 1/4 20 tap or a bottoming tap?
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It's tapered.

I'm not going to fuss and cuss trying to tap it from the inside; if I can't get the bolt, I'll do on the passenger side what I did on the driver's side, which is drill through the tailgate to tap the hole.
 
Just use a 1/4" self-tapper and move on.

Nobody will see it from the other side.
1724951603457.png


To be honest, I will wager there's something else going on here. I highly doubt broke-*** Chrysler would blow coin on a weird limited-application screw when a 1/4-20 would work.
 
jos51700 said:
Just use a 1/4" self-tapper and move on.
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If I snapped the head off of a 1/4" bolt with the correct TPI trying to get it in the hole, I'll do the same with a 1/4" self-tapper. The issue is that a 1/4" shank is too big.

I like the idea, but I'm not seeing 7/32" self-tappers. Be willing to try, though, if you have a link.

To be honest, I will wager there's something else going on here. I highly doubt broke-*** Chrysler would blow coin on a weird limited-application screw when a 1/4-20 would work.
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What is a weird limited-application screw in 2024 might not have been 61 years ago. Just sayin'.
 
shortmort37 said:
If I snapped the head off of a 1/4" bolt with the correct TPI trying to get it in the hole, I'll do the same with a 1/4" self-tapper. The issue is that a 1/4" shank is too big.

I like the idea, but I'm not seeing 7/32" self-tappers. Be willing to try, though, if you have a link.


What is a weird limited-application screw in 2024 might not have been 61 years ago. Just sayin'.
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In rough finished holes, they won't go to 1/32" increments. The self-tapper sizes the hole correctly for the thread, where your existing hole won't fit a 1/4. I'm operating under the assumption that these are threaded in sheet metal.
 
jos51700 said:
In rough finished holes, they won't go to 1/32" increments. The self-tapper sizes the hole correctly for the thread, where your existing hole won't fit a 1/4. I'm operating under the assumption that these are threaded in sheet metal.
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Judging from the one hole I drilled and tapped through the tailgate, there’s a welded nut on the plate through which the screw goes. Perhaps I can get a picture.
 
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shortmort37 said:
If I do a self-tapper, I need 7/32, not 7/16.
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yes sir I get it. The bolts in your post you said are 7/16 20. Then you posted a hydraulic system banjo bolt with that same thread. I was just trying to help you get a replacement bolt for your original damaged bolt. Not a sheet metal screw. Typically these pieces do have spot welded nuts or some sort threaded body fastener. The nuts can usually be tapped but the clips or fasteners not so much. An any event if the original bolt you posted is a 7/16 20 they can be bought. PEACE OUT good luck with your project.
 
jeff alder said:
yes sir I get it. The bolts in your post you said are 7/16 20. Then you posted a hydraulic system banjo bolt with that same thread. I was just trying to help you get a replacement bolt for your original damaged bolt. Not a sheet metal screw. Typically these pieces do have spot welded nuts or some sort threaded body fastener. The nuts can usually be tapped but the clips or fasteners not so much. An any event if the original bolt you posted is a 7/16 20 they can be bought. PEACE OUT good luck with your project.
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Thanks, Jeff - I appreciate your efforts. I did correct myself to 7/32-20, perhaps you missed it.
 
shortmort37 said:
Thanks, Jeff - I appreciate your efforts. I did correct myself to 7/32-20, perhaps you missed it.
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no problem I was looking at post #14 for the bolt...which says what is says. Use a bolt if you can with some anti seize. Self-taping screws are one time in and not serviceable. They also loose their tightness in a moving vehicle going over bumps.
 
jeff alder said:
no problem I was looking at post #14 for the bolt...which says what is says. Use a bolt if you can with some anti seize. Self-taping screws are one time in and not serviceable. They also loose their tightness in a moving vehicle going over bumps.
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Jeff, not only was I mistaken about the bolt, I was imprecise in my response!

Oops. 7/16, not 7/32. My bad.
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I meant to say, the link was to a 7/16 bolt, not the 7/32 that I needed. Mea culpa.

That's a good point about self-tapping screws; even if I could get a 7/32 one, I don't think that's a solution. I'm going to try tapping 1/4-20 from the inside - again - before I give up and drill/tap from the cargo side of the tailgate.
 
shortmort37 said:
Jeff, not only was I mistaken about the bolt, I was imprecise in my response!



I meant to say, the link was to a 7/16 bolt, not the 7/32 that I needed. Mea culpa.

That's a good point about self-tapping screws; even if I could get a 7/32 one, I don't think that's a solution. I'm going to try tapping 1/4-20 from the inside - again - before I give up and drill/tap from the cargo side of the tailgate.
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I bet you at least know how to spell lose. Not like me loose. LOL Do it once and do it the best way possible. I repair equipment all day everyday so I try and help with repairs when I can. Dont give up...the quick and easy path leads to the dark side! LOL
 
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