Need help with roll bar

Hello, so I have bought a roll bar for BMW E36 coupe from AST and I ran through a problem while installing it and since they are ignoring my emails, I decided to leave a post here maybe someone with good knowledge can help me.

So the roll bar comes with 4 reinforcement plates that need to be welded to the body (its not a 100% bolt in roll bar, you still need to weld). Now the reinforcement plates that came with the roll bar are suppose to be a perfect fit for BMW E36 coupe floor using laser scanner technology.

Now this is my reinforcement plate, where I marked with green is where it should be welded and where I marked with red is where the problem is, the holes aren't touching the floor. Now if I understand correctly I need to drill 4 holes in the body to bolt the roll bar feet with the welded reinforced plate. So my question is here since 2 of them aren't touching the ground can I just weld 2 nuts with the reinforcement plate instead of drilling the body since there's alot of clearance between the plate and the floor? As for the 2 other holes they are flush with the floor.

Also would welding these plates with a MIG welder be enough? Or do I need to find someone who uses TIG? Also since I'm going to be welding the plates in, are plates from under the body nessary would they add more strength? Or should I use only washers for the bolts underneath?

Welding all around that seals the area under the hole from the elements.  I'd imagine you are supposed to drill a large hole in the floor under each bolt to allow the nut to be inserted from beneath.  Welding in the supplied nuts would potentially work in that application however I would advise against it as the fastener strength would be effected by the heat from welding and generally sanctioning bodies require the fasteners be a specific Grade (5/8, 10.9 if metric, AN etc.) And you can't very well claim a grade after you've heat treated it.   Weld nuts that have ratings are available but large hole is easier.  

I'm a big user of welding normal nuts in as captive Nuts but don't do it for fasteners that require ratings. 

Another option would be a sleeve around the bolt between the floor and plate and use longer bolts.  

Yes, drill 4 holes in the body to bolt the roll bar to the floor first. When you tighten up the bolt I imagine they will pull the floor closer to the bar's feet. The distance doesn't look like much from the pic.

In reply to nocones :

Yes I thought about that as well, the thing is that I'm feeling guilty drilling the floor board which such big holes that's why I wanted to weld them before welding in the plate. What if I use a high grade nut to weld? Or maybe weld a 12.9 bolt instead? Thanks for the reply.

Sorry for double posting but I'd like to add another question, would welding these plates with a MIG welder be enough? Or do I need to find someone who uses TIG? Also since I'm going to be welding the plates in, are plates from under the body nessary would they add more strength? Or should I use only washers for the bolts underneath?

Many roll cages are welded with MIG all the time.  It helps if you pre-heat the thicker metal first with something like a propane torch so that the thicker material doesn't "steal" all of the heat when you try to weld the thick to the thin. 

My Datsun was an Autopower cage kit. We actually welded the plates on the underside of the car after it was all bolted together.

MIG is fine.  It might even be better in this application because it's less sensitive to contamination.  Not that you don't want to get as much bare metal as you can.

Weld the plates in per the instructions and use the bottom plates. The bottom plate distributes the load across more of the floor than washers will.  When you tighten the fasteners it'll pull the floor up to the top plate.  If you want to help it a little take a big hammer and bash the floor up against the top plate after it's welded in.

In reply to APEowner :

Unless I'm misunderstanding what you're saying, I don't think the floor is going to pull up in any meaningful fashion. That plate looks like it has stand offs on the right and lower side to bridge the gap to the floor. If It's welded there then it would prevent the floor from coming up. 

I see a hole saw in your future.

iansane said:

In reply to APEowner :

Unless I'm misunderstanding what you're saying, I don't think the floor is going to pull up in any meaningful fashion. That plate looks like it has stand offs on the right and lower side to bridge the gap to the floor. If It's welded there then it would prevent the floor from coming up. 

I see a hole saw in your future.

It depends on how big the gap is between the top plate and the floor and how big the bottom plate is.  I was assuming (and I think I see in the pictures) that the floor profile is similar to the plate but that it doesn't quite make contact in the area near the front holes.  Perhaps a picture without the plate would be helpful.

In reply to APEowner :

They did not give me plates for the bottom its not included but I could make them

In reply to APEowner :

I will take more pictures tonight thanks

In reply to nocones :

On the instructions that comes with the kit it says the way you told me. To drill a large hole and insert the nut from there but it also says to weld the nut in place afterwards. Doesn't make sense to weld it afterwars when I can just weld it while the plate is out.

Mig is fine

If you're going to be welding to the car, why not just weld the bar in?  How often would you be removing and reinstalling it to justify a bolt-in?

Jvella36 said:

In reply to nocones :

On the instructions that comes with the kit it says the way you told me. To drill a large hole and insert the nut from there but it also says to weld the nut in place afterwards. Doesn't make sense to weld it afterwars when I can just weld it while the plate is out.

You don't know where it is going to want to be until the unit is fully assembled, so you don't weld any nuts in on the bench.

Steel will bend and flex and moosh a LOT.  Unless the gap you are talking about is like 3/4" i would just bolt it all together. 

In reply to jfryjfry :

I also thought about doing that but then I should have bought a weld in cage instead. I didn't pay attention of that plates need to be welded before I bought it. I thought it was a 100% bolt in cage where you just place a reinforcement plate from underneath and sandwich the body between the plate and the cage 

In reply to Pete. (l33t FS) :

Yes but if I'm just gonna bolt those 2 holes directly to the cage instead of putting them through the body, it wouldn't make a difference if I weld the nuts on bench

Tom1200 said:

My Datsun was an Autopower cage kit. We actually welded the plates on the underside of the car after it was all bolted together.

Well, sir, I have a story for you. Autopower had a fire in their shop long ago, so had to create new template units for various cars. I learned that they were looking for a Datsun 1200 to borrow in order to take measurements from, so I stepped up, and acquired a new rollbar in trade. So, your cage got its measurements off my car. That was way back in about 1982 or so :)

In reply to APEowner :

Here are some more pictures, dont mind the holes in the body I will be closing those, they are from a previous roll cage. 

As you can see the 2 holes match exactly with the "steep of the body" so that's what's making the clearance.

I'm also currently preparing the rear strut towers to weld in the plates and I found some holes due to rust, should I weld these shut before welding in the plate? Thanks

and I found some holes due to rust, should I weld these shut before welding in the plate? 
 

Yes an then cover them liberty with a weld through primer

In reply to dean1484 :

Alright thanks mate

Can someone please help me understand this?

What's the point in doing a big hole to insert the nut and then weld it, when I can just weld the nut while the plate is out and doesnt welding the nut ruins tensile strength?

Thanks for the extra pictures.  Now that I can see the situation better I agree with those that indicated you're not going to be able to drive the floor up enough to have it make contact on the front holes.

Welding the nuts does technically affect the hardness.  They will harden in the weld zone.  However, you're not holding them at the high temperature so you won't anneal the threads which is the part that you care about.

This is the installation process I'd probably use.

1. Bolt the plates finger tight to the bar using the front bolts
2. Position the bar in the car with the plates attached
3. Tap the plates into the corners so that they sit where you want them
4. Pull the bar/plate assembly out of the car and weld the nuts in place
5. Put the bar/plate assembly back in the car and tack the plates in place
6. Pull just the bar out and fully weld the plates in
7. Drill the holes through the floor for the rear
8. Bolt the bar in place using big washer or a backing plate on the rear holes and the welded in nuts on the front holes

You probably know this but you need to get all the seam sealer out of the weld area before you install the plates.

In reply to APEowner :

If it is like the R53, I think they actually spot welded the tub THROUGH the sealer   It is as if they spackled the weld area with thick adhesive before assembly, spot welded the tub, then smoothed it over while still wet.

100% penetration between panels when trying to drill out the spot welds to remove panels.