HD Roll bar. Where did I eff up?
 

Been trying to get the roll bar in for two days and finally have everything drilled, aligned, and (mostly) bolted.

So I'm trying to get the seat belt tower bolts in i.e. the ones connecting the roll bar to the top of the tower(near where the oem seatbelt bolt goes in) and I can't get it to go in at all.

I've tried both the stock bolts and the hard dog bolts and this is what they look like now.

Attachment 230398

Attachment 230399

Attachment 230400

I'm wondering if I should try to tap the threads on the seat belt tower to see if that's the issue, or if I should just drill the threads out of the car and put a bolt on the other end.

I never expected this to be the hold up. Everything else is bolted in, but not fully tightened, so the alignment should be good. It looks like it's going straight in but apparently not...
Does anyone know what size/thread that bolt is so I can tap it? I'm looking up stuff on this right now as well to figure out what it is stock.I can take the bolts with me to a hardware store tomorrow to see what they thread into.

Hard dog lists them as:

• 2 - 7/16"(11mm) X 2.25" bolts (I'm guessing they're the 20 TPI one which is the fine thread as the other option is 14 TPI)

Any advice would be appreciated! Thanks in advance.

(I cross posted this across the pond just to see what folks at mnet thought as well)

Re tap for OE bolt. Drill larger hole in the tab, get new OE bolts. Win.

If retapping doesn't work for whatever reason, is drilling out the hole and putting a nut on the other end a viable option?

7/16X20TPI. Oddly enough federal law required SAE bolt not metric.

Yeah, I actually just found a thread talking about this! Apparently they say SAE or equivalent but folks just use the SAE for the US instead for liability reasons I'm guessing.

When mine did not line up, the roll bar was too wide, so we pulled it in using a rachet strap between uprights. Yours looks too narrow, so you may need a way to jack them apart.

You will have to re-tap the hole first. Then by some means like an off-roader's jack, tighten the bolt, then remove the jack.

https://cimg0.ibsrv.net/gimg/www.mia...89e11d3910.jpg

My roll bar bolt holes had that problem, not lining up perfect. I used clamps and a strap to "bend" it enough that the bolts would go in by hand and not try to cross thread.

If you've damaged the threads out of the factory seat belt mounting hole, I would be hesitant to simply clean them up with a tap. That's going to wind up weaker than factory, and the seat belt mounts are kind of important...

Is there enough meat around them to drill out and put in a helicoil?

--Ian

From what I can see, the bolts were softer than the nut, so the bolts are what sheared and were stripped. I think the guts inside are the leftovers from the bolt threads.

In any case, I definitely think you have a point there re:safety. I'll be sure to thread an additional grade 8 nut through the other side so there are more threads there as well. Do you think that would be sufficient in this regard?
I was originally thinking of just drilling through and putting a bolt on the other side, but I think you're right that a helicoil would be far smarter than that due to the number of threads and safety aspect.

A little hard to see here, but things lined up pretty well in the final mounting spot. Unfortunately, it seems like the damage was done already...



https://cimg6.ibsrv.net/gimg/www.mia...d7c9220b84.jpg

If I still have an alignment issue (which I don't think I do), I'm guessing widening the opening on the roll bar isn't a good plan, right?

The one true standard across cars, oddly enough. Kind of nice to be able to bolt Elise seats into a Miata and have the seatbelt fasteners swap across, though.

I'm almost positive you're using the wrong bolt.. Mine don't have that little hump below the bolt head.

there should be a washer for a plastic cover (to cover the bolt) on that bolt right below it instead. I remember using them, you should have them.

Which hump are you talking about?

This is from TDR's site for HD roll bar hardware.

https://cimg4.ibsrv.net/gimg/www.mia...dfaaed91fd.jpg

Edit: I see what you're talking about now. I think I have that bolt as well and the same thing happened there too. I also just double checked the alignment and the bolt sits right on top of the threads when it's in the hole on the roll bar.

Here's the other bolt as well.

https://cimg0.ibsrv.net/gimg/www.mia...a7026631dd.jpg

Opening the hole 1/16" would be OK, I would think.

In the first pics, I suppose due to camera angle, they didn't look aligned to me.

Ah, sorry about that. In the first post I was trying to show what the threads in the seat belt tower 'nut' looked like. I had my phone at an angle between the bar and the seat belt tower to focus on the inside of it. I think the frayed edges are from the stripped bolts or so I hope.

If memory serves me right, 7/16x20TPI also just so happens to fit the spec for an M11x1.25 thread. I'm pretty sure they work interchangeably, even though they may be at the limits of each others' specs.

M11?!

From hard dogs website:

• 2 - 7/16"(11mm) X 2.25" bolts

Guessing the 11 means M11 here so even HD says it's interchangeable. Stefan's basically my miata sensei at this point so I just shut up and listen to him and do what he tells me to.

Miata Xtreme, Hard Bar Sport, M2 Sport, Hard Core Hard Top Installation Instructions

There is an M11 in ISO thread. But not in a 1.25 pitch.
M11X0.5, M11X0.75, M11X1.0, M11X1.5

I priced out new hardware because I've read that it's not really recommended to re-use the hardware on these.

I'm just going to call hard dog and get the hardware kit and order the vinyl cover with the SFI padding.