Question on fastening of roll bar

Hey guys, I am looking at attaching the roll bar that I picked up for my B and since it has sat for a couple years we are having trouble figure out the way it should be attached. The rear arms are made to sit on the edge of the rear shelf and fasten on the lower side of it, the front arms sit just inside the door sill along the seats. Here are a couple pictures to show how they sit when sitting in the car near the proper position. Looking at the rear shelf I believe that if I were to drill through I wouldn't be able to access the back of the bolt to attach it, how do you recommend doing it? Thanks, Michelle

You'll be able get to the bolts via the rear wheel well for the footings that rest on the rear shelf(I have a bar that mounts there as well).

It's the bolt that mounts to the inner sill by the seat that's going to a pia. Looks like you'll have weld in a captive nut for tht one.

You will want to make a piece of steel that equals the size of the foot you are mounting, and put that piece on the underside. The sheet metal should be sandwhiched between the roll bar foot and the piece of steel. I think grade 8 hardware is recommended for mounting a roll bar.

Brad

"You will want to make a piece of steel that equals the size of the foot you are mounting" spot on Brad!

Sounds like the bolt to the sill is the pita to me. Maybe for 10 bucks I should have left it in the pick n pull. If anyone has installed this and has any photos that would be helpful. We were trying to get it in so I could install the carpet but ..... we will see.

You need to plate the bottom of the rail as mentioned above but also you need to make some tubing spacers and weld them to the bottom plate that the bolts will go through to keep from collapsing the box section as you tighten the bolts. The plate on each side only works for sandwiching a single thickness of metal to spread out the load.

Or tack weld a grade 8 nut to a hardened washer, cut a hole with a hole saw & weld the washer in the hole with the nut facing down into the sill.

Personally, I think that the roll bar plates need to be larger. I have four bolts in each plate on my roll bar.

We drive sheetmetal cars. Even the box sections that look like they might be a frame are just more sheetmetal. Look at the ares where the front suspension bolts onto the front end. There are reinforcing plates welded in and tubes that pass through the box section. Unless rollbars are adequately mounted with plates that spread the load over a wide area the bar can punch through the sheetmetal. Also good to have the mounting plates attach in 2 planes 90 deg to each other since sheet is much stronger standing on end than in the flat.

I think add-on rollbars give us a false sense of security - most of them are more cosmetic than functional.

A roll bar that will allow me to raise and lower my top would be lower than the top of my head when setting in the drivers seat. Better yet, don't drive like a idiot and be defensive.

The question is... is a roll bar (even a poor one) better than nothing in a rollover?

I for one think some protection is better than none.

A friend who builds and races a lot told me to "duck" if the roll bar is not high enough!

Brad

I think a roll bar that is not properly braced is dangerous. There is the problem of it folding over of course....but another significant problem is hitting your head on it in a collision. Nothing more dangerous than a full cage in street car with no helmet and just a stock 3 point belt. I've seen racers hit their helmet on a cage or bar hoop even when fully belted in tight with a 6 point........

better than nothing? not really............

Having been involved in both a rear-end collision and a rollover (not in the MG BTW), I really don't know which I would prefer in my B - my head colliding with a rollbar or turning into a sardine.

You can add SFI density padding to a roll bar to reduce incidental impact... hard to add SFI to the dirt where your car rolls!

An idea for the sills

http://www.pemnet.com/design_info/about_blind_inserts/index.html

Steve, I like the looks of those but I wonder which of the ones available would work the best for fastening it down?

Those usually require a special tool to install. I wouldn't use 'em to bolt down a roll bar, though.

In the tubs that Heritage makes for racing, they have roll bar anchor plates with threaded inserts already installed... that's the idea Im thinking of... where to get the parts to execute it is the question.

http://www.britishv8.org/Articles/BritishMotorHeritage-Competition.htm

Here's a better picture

If you look closely at the picture, the mount is a piece of plate that looks to be about 1/8" that covers a relatively large area and is welded all around to the sheetmetal. The plate is also bent 90 deg and that is welded to the box section in the vertical plane. You can't tell from the pictures but I would bet that the plate has nuts welded on the underside. This is a lot more than threaded inserts in the sheetmetal. I'm sure the other rollbar attachment points are similarly braced.

Design the plate... weld nuts to underside of plate... relieve hold in sill to clear nut... weld plate to sheet metal structure???

Well that doesn't look too bad. Do you figure they a small section where the nuts would be welded on or do you think the nuts are only the thickness of the metal piece? It looks to me like it is bent with a 90 degree angle as you mentioned.

Michelle... on the one hand I don't want to down play safety, but on the other we are talkin a street bar.

A plate in two planes would be the strongest, but we are talking street here. A single plate in a single plane, welded to the sheet metal would be a huge improvement over every other street application I've ever seen.

I think I would look for the tallest nut I could find to weld to the back of the plate so that as many threads as possible are engaged. I think I'd also get captive nuts with round bodies so I could weld them into a hole cut in the plate, rather than just welding them to the surface.

When does overkill stop?

http://www.alibaba.com/showroom/stainless-steel-round-nuts.html

Michelle:

The bar you show looks to have been installed for looks more than anything else. Steve's illustration is the way to go with the bent plate welded in. You still need to modify your bar so that the mounting foot has more area and room for two 1/2" grade 8 bolts. The same needs to be done to the upright mounts.

As for thread depth, rule of thumb for me is 2 times diameter of bolt should be the max for strength. So for a 1/2" bolt, there would be 1" worth of thread in the hole. The goal is for the bolt to break before the thread strips. I COULD argue that the load will never be a straight pull on the thread, and hence you can get away with less thread and it would make no difference, but I won't!

Looking at steve's second picture, not sure I approve of how the belts are anchored into the rear bulkhead; that is just a sheet of tin.

Pete

Here's how I've done it in my GT that is being built for UK motorsport events. I turned down M10 nuts in the lathe so that they would register in the holes in the the plates, then I TIG welded them all round. The plates are 3mm thick and the front ones go down into the side of the sill and into the floor. The ones on the heelboard have been extended from the FIA legal size by TIG welding extensions to go down the heelboard and into the side panel. I have also TIG welded 8 brackets to the cage to bolt into on the A and B pillars. It may seem like overkill, but I rolled my Escort into a tree on the Hunsruck Rally in Germany and I was glad of the strength!
MGB roll cage front mount
MGB roll cage rear mounts
MGB roll cage bolt brackets

rosette welds where practical will also help to distribute imposed loads.

Well I have made the executive decision not to install the bar, I was worried anyway that since my husband is 6'4" that when he leans the seat back to be comfortable under the top he would be hitting too close to the bar. So after thinking it over I decided not to put it in, but I thank everyone for the advice and if you are close by and need a roll bar come on over lol...... good deal to be had. :)

Michelle,

Just make sure he keeps the shiny side up:)

More seriously, I'm about the same height and always had doubts about what would happen if the car rolled. That is until a number of yeats back I got into an icy situation at about 45 MPH and the car broke loose and I ended up going down the road sideways for about 200 feet. The car only stopped when I hit the shoulder sideways. It hardly gave a thought to tipping. Maybe my experiance is not the norm. I expect the race guys have different opinions but these cars seem to be pretty stable to me.