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> HeliCoil Seat Belt Mounts, bad idea?
McMark
post Oct 21 2005, 11:43 AM
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I have seat belt mounts that have stripped threads. I'm wonding if HeliCoil's are strong enough in case of an accident. Logic tells me, yes they would be fine if installed correctly, but my gut is a little more nervous than my head. Can anyone tip the scales one way or the other for me?
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ArtechnikA
post Oct 21 2005, 11:47 AM
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i have been down this path too, since there are *no* seat belt mounts in the tub of a '71 911 Targa...

i think i'd prefer a TimeSert over a HeliCoil, possibly with a bit of tack weld on the head...
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Aaron Cox
post Oct 21 2005, 11:49 AM
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id be scared.

weld up and retap? (IMG:http://www.914world.com/bbs2/html/emoticons/w00t.gif)
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jhadler
post Oct 21 2005, 12:46 PM
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Reminds me of an old Bell Hemlet add campaign...

"If you've got a $10 head, buy a $10 helmet".

In my opinion, seat belt anchors are one of those things that you can ill afford to do half-assed. Get it welded up and do it right. Timeserts and helicoils are great for some things. And while I might trust my engine to one, where precision is the most important thing, I don't think I'd be as comfortable trusting my life to one, where -strength- is the most important thing.

Just my $0.02...

-Josh2
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ArtechnikA
post Oct 21 2005, 12:58 PM
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QUOTE (jhadler @ Oct 21 2005, 02:46 PM)
-strength- is the most important thing.

strength is important, but it is not absolute.

i haven't cut up a tunnel or a B pillar to verify, but my understanding is that the OEM part is not merely tapped into the sheet metal, but is itself a threaded insert welded into the local structure.

so at best, you could weld the outermost part closed and retap that, but i don't think you're going to be able to fill the whole insert with good weld material.

the seat belt anchor mostly takes up a load in shear, so that's the strength you're concerned about. as long as the anchor can take a load perpendicular to the shank axis, it'll do its job.
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jhadler
post Oct 21 2005, 01:03 PM
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Yes, it's a welded in insert. But look at the insert, it's a far cry heavier than a timesert. And shear is certainly the key. I dunno, I guess I'm just a stickler for things like that. I like the knowledge that my belts will do their best to keep from hitting hard things (dash board, windshied, etc.) with soft things (me).

-Josh2
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goose2
post Oct 21 2005, 02:37 PM
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drill them larger and re tap for a bigger bolt?
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dlo914
post Oct 21 2005, 03:03 PM
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speaking of seat belts...has anyone tried installing a 3rd seat belt for the center "seat"?
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McMark
post Oct 21 2005, 06:33 PM
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Early cars have the supports and threads in place already. Stopped in 73 I think. For those cars it's a bolt in and you're done.
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banksyinoz
post Oct 21 2005, 07:43 PM
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QUOTE (goose2 @ Oct 21 2005, 12:37 PM)
drill them larger and re tap for a bigger bolt?

this is probably the best option if u cant get to the other side of the panel in question (i havent had to look yet) if you can you could replace the nut (weld nut to 3inx1in 10mm thick plate if doubtful this seems to be a manufacturing standard) then away you go or just use a bigger bolt
i know i certainly wouldnt use a helicoil
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Trekkor
post Oct 21 2005, 08:41 PM
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QUOTE
I have seat belt mounts that have stripped threads


Mark, is this your car or a customer's car? (IMG:http://www.914world.com/bbs2/html/emoticons/confused24.gif)


KT
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nebreitling
post Oct 21 2005, 09:17 PM
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boy, that's going to be a tough fix. even over-tapping might not be great unless you can ensure some good threads.

but i would not personally strap into a heli-coiled belt ancor, and i'd sure as hell not put a loved one in that seat.
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McMark
post Oct 21 2005, 09:19 PM
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I'll have to agree with Rich's point that it's a shear load issue. The threads aren't what are doing the life saving. The threads are just to keep the bolt from falling out. I think that for the amount of material that is there makes TimeSerts less appealing to me (you'd end up thinning the wall of the support structure). Welding is probably the best option as long as you are a certified and trained welder with years of experience. Welding sheet metal and body pieces is one thing, welding shut what will basically become 3/4 thick material is completely another. Having heard some opinions and had a chance to think about things, I think HeliCoil is probably what I'll go with.
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John
post Oct 22 2005, 12:13 AM
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As I recall, the seat belt bolts have an unusual (at least to me) thread. I once had to get a tap to chase the threads out on one of mine and I had some difficulty finding the right tap. If you can get helicoils in that size I would be surprised. I would think about replacing the seat belt anchor. I know it might be a big pain, but at least you would know that the new anchor was strong.

just my $0.02
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McMark
post Oct 22 2005, 12:25 AM
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Yeah, it's 12 mm x 1.25. Most 12 mm bolts are 1.5 or 1.75. I can get the HeliCoils. I've already done the research. (IMG:style_emoticons/default/wink.gif)

[EDIT]M11x1.25 NOT M12. Whoops.. (IMG:style_emoticons/default/pinch.gif)
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neo914-6
post Oct 22 2005, 12:28 AM
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The band-aids aren't worth the liability. Did the bolt mount get cross-threaded or was it worked free by belt movement over time?

Weld a nut or thread insert to a small plate with a hole, drill out the hole in the chassis to fit the nut and weld the assembly...
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McMark
post Oct 22 2005, 12:37 AM
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It looks like the threads were torn out during disassembly. A thread inset in a factory boss seems like a much safer solution to me than a complicated construction. I prefer a single point of potential failure, rather than a whole mess of them.
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banksyinoz
post Oct 22 2005, 11:27 PM
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QUOTE (McMark @ Oct 21 2005, 10:25 PM)
Yeah, it's 12 mm x 1.25. Most 12 mm bolts are 1.5 or 1.75. I can get the HeliCoils. I've already done the research. (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif)

nissan exhaust manifold stud size from memory?
doesnt sound real big though

i will go check
(IMG:http://www.914world.com/bbs2/html/emoticons/confused24.gif)
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John
post Oct 22 2005, 11:46 PM
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If you feel comfortable doing it, go with the helicoils.

The load is in shear, so we are not talking pullout. The only problem I see with the helicoils is getting the tang to break off correctly to allow the bolt to fully seat without screwing the helicoil out the back side of the anchor point.

In other words, go for it.
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ArtechnikA
post Oct 23 2005, 06:19 AM
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QUOTE (McMark @ Oct 22 2005, 02:25 AM)
Yeah, it's 12 mm x 1.25. Most 12 mm bolts are 1.5 or 1.75. I can get the HeliCoils. I've already done the research. (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif)

you have started the research; it will be complete when you discover that seat belt bolts are 7/16" 20 tpi.

there are a few places where Amrican sizing is used; this is one of them.
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