Fitting bolt in cage - bit of advice needed

[drjim]

Chaps

Been lurking on 10/10ths for a while but not posted before. I am building a BMW E21 track day car, will have a turbo M10 engine, LSD, LEDA coilovers, pedal box/bias brakes, much lightening etc. My intention is to do trackdays and see what happens rather than trying to race from the beginning.

I have just started fitting an OMP bolt in cage, it just about fits OK, and comes with some steel plates to weld to the floor as footings. I have started at the B-pillar, and am trying to build it up as much as poss so it is nearer to the roof than my head (I have removed the headlining, so there's a bit more room than OMP designed for). Is this the right approach?

So should I just use the plates that came with the cage so as to keep the bottom of the cage as near as possible to the floor, bolt it through and stick another plate underneath (I was planning to do a bigger plate at 90 degrees to the top one to increase the reinforced area). Or should I build some platforms to get another 2CM clearance above my head?

I have made up some bits to do the buildup option, clearly welding in the basic plates is theoretically easier, but will require bits around to match the floor profile.

Any opinions???

Jim

[MGDavid]

are you very tall? it sounds as if you are expecting height / clearance issues, bearing in mind the blue book requires 2 inches clearance between the top of your helmet and the (lower surface) of the cross tube of the roll cage. Then again it depends on your choice of seat and mountings - in a saloon you can often get any extra head clearance you need by canting the seat back further but that doesn't suit everyone, for instance it leads to more issues if you wear bifocal or varifocal specs (as I do). If you don't actually need the extra headroom then just weld the plates directly to the floor and bolt the cage in. Making little platforms to get the maximum height is a fiddly job and needs to be done carefully to retain strength.

[drjim]

I'm just about 6 foot, so massive clearance isn't an issue. I just wondered whether it was better to get it tight to the roof or leave a gap.

Thanks for your advice, I'll keep the buildup minimal and leave more of a gap.

[Notso Swift]

Welcome aboard!

Purely as opinion, the cage was designed to be fitted in one way, then that is what you should do.

Spacing may lead to other fitment problems, indeed it mopst probably will

[drjim]

Good point there, but the plates they supply don't directly "fit", so it requires a bit of building up. I will take my camera to the workshop next week and get some pics of what I've done so far.

[Jim Lamb]

Speaking from experience of 'Cutting' errant drivers out, the better constructed cars always have the cage tight to the existing Body structure or attached with 'web plates'.
If you can Build the foot mountings up, without compromising the structural integrity of the cage design, do so, but make sure they are substantial Base structures and dont forget if it's a bolt in cage plenty of large metal plates or washers either side of the bodywork to reinforce the Holes, to stop the bolts punching through.

R's Jim

Jim Lamb

Ex Rescue Crew

[drjim]

I was planning to weld some gusseting between the pillars and cage to help stiffen things up, I think the best approach is to weld the basic platforms in, then decide whether to fabricate some box sections to space the cage feet up a bit.

As an A&E Consultant I've dealt with plenty of injured drivers (road rather than race), so want to do my utmost to avoid problems myself!

Thanks for the opinions.

Jim

[Leighton Irwin]

If you are going to raise the cage suggest you use solid metal plates rather than a box sections. Yes they will weigh more but will be stronger than a box in this application, although if the ends of the box are closed it will be fairly strong. What kind of welding are you doing? I would not use gas for this purpose.
If the cage was designed by a reputable company for your specific car I would hesitate to modify it with the possible excetion of a larger plate under the floor. Whatever you do, use top quality bolts, washers and locking nuts and check them regularly. If the nuts and bolts supplied are only grade 5 (automotive) buy better ones. If you do raise the cage you will need longer bolts anyway. Make sure all holes are exact so there is no slop. Military spec hardware (aircraft) bolts are exact. Grade 5 are not. If you are lucky you may have an aircraft surplus outlet near and you won't have to pay through the nose for your hardware.
Old fart race mechanic here.

[terence]

The bolts supplied in the fitting kit should be 8.8 anyway,therefore plenty good enough for thier job.Jim,dont forget that all plates need to be 3mm thick.As has been said,you do need 50mm clearance between the underside of the cage to the top of your helmet,this will depend the seat being used and how high you sit in it obviously.Have you had a dummy run with the fitting,all you need put into the car is the main hoop,then sit in the car with your helmet on to determin what room is availabe/needed.If needed,personaly I would not take the solid plate route,because the pressings in the floor pan will make welding in more difficult,far better to creat your own mounting platforms/box sections,you only need to weld nuts to the underside of the top face on these platforms obviously in line with the holes in the cage mounts.

[drjim]

The cage came without bolts to fix it to the floor, I have a stash of 8.8 tensile bolts to use. Hadn't thought of welding nuts under the platform, was planning on bolting through the platform and floor with a large plate underneath.

[terence]

Originally Posted by drjim

The cage came without bolts to fix it to the floor, I have a stash of 8.8 tensile bolts to use. Hadn't thought of welding nuts under the platform, was planning on bolting through the platform and floor with a large plate underneath.

Only increases the opportunity of water leak's.As long as you use the 3mill plate,there is absolutly no need to go all the way though the floor. 8.8 bolts will be fine,thats what most cage manufacturers use.

[terence]

Originally Posted by drjim

The cage came without bolts to fix it to the floor, I have a stash of 8.8 tensile bolts to use. Hadn't thought of welding nuts under the platform, was planning on bolting through the platform and floor with a large plate underneath.

Only increases the opportunity of water leak's.As long as you use the 3mill plate,there is absolutly no need to go all the way though the floor. 8.8 bolts will be fine,thats what most cage manufacturers use.Dont forget the bolts need to be 17mm.

[MGDavid]

just for clarity, the book says min M8 bolts, 17 mm is spanner size of course ;-)

[terence]

Originally Posted by MGDavid

just for clarity, the book says min M8 bolts, 17 mm is spanner size of course ;-)

Yes of course. [sorry for double post,dont know what happened!]

[Mik]

Originally Posted by MGDavid

bearing in mind the blue book requires 2 inches clearance between the top of your helmet and the (lower surface) of the cross tube of the roll cage.

I thought the 2 inch minimum was between the top of your helmet and the top surface of the cage, not the lower one.

In fact looking in the blue book, the diagram "Drawing No. 31" in section C(c) shows this. (OK, if I'm being pedantic it shows a 5cm distance!)

Probably not relevant in this particular case anyway but I thought it worth mentioning.

[JohnD]

Dr.Jim,
Have a read of your Blue Book - other Drawings in what used to be Section Q, oq "Competitors: Safety [C(c)]" (sigh) offer good advice. See Drawings 17,18, p172.
I think the latter shows a spacer, with a compression tube for the bolt - very strong - so that the boxed in section can be closed completely as no access is required to reach the bolt head as in 17.
JOhn

[drjim]

Hi

I don't have a blue book, but I think I get what you are saying.

Jim

[MGDavid]

Originally Posted by Mik

I thought the 2 inch minimum was between the top of your helmet and the top surface of the cage, not the lower one.

In fact looking in the blue book, the diagram "Drawing No. 31" in section C(c) shows this. (OK, if I'm being pedantic it shows a 5cm distance!)

Probably not relevant in this particular case anyway but I thought it worth mentioning.

Very good spot Mik, it also states it in para. C(c) 39. Less to worry about for my 6'3" mate who shares my car sometimes....

[terence]

Originally Posted by JohnD

Dr.Jim,
Have a read of your Blue Book - other Drawings in what used to be Section Q, oq "Competitors: Safety [C(c)]" (sigh) offer good advice. See Drawings 17,18, p172.
I think the latter shows a spacer, with a compression tube for the bolt - very strong - so that the boxed in section can be closed completely as no access is required to reach the bolt head as in 17.
JOhn

Which is why the nuts should be welde to the underside of the mount face before its all welded together.

[drjim]

The feet at the B-pillar have 4 bolt holes, two of which will sit directly over the inner sill. I was contemplating fitting another box section piece on top of my newly welded in feet, but some electrical conduit cut into short lengths inserted from below as spacers might work better. I'll have a look at it if I get to the garage next week.

Found some blue book pics online, so I know exactly what everyone is talking about now!

Jim

[MGDavid]

you only need 3 bolts per footplate so you have a choice on the B pillars, no point in making it too difficult!

[Alan Cherry]

Going back to your earlier question where you have room to raise the cage by the B posts - have you bolted the cage together first to check the fitt at the other mounting points ?
I've just fitted a cage to a Rover 220 Turbo Coupe - a SD cage from one of the Tomcat cars, but with a new fitting kit supplied by safety devices- ok, it's a 23 point cage, but when you bolt it all together inside the car, there is only one possible way it can fit - In fact when bolted up, you would think it was welded in ! - If you raise the central hoop, you may give yourself problems elswhere. My fitting kit came with trapped nuts welded to the plates with the main hoop supprts either resting directly on the box section, or horizintally on the side (If that makes sense). My sequence of events was
1. take seats and dash out of car
2. mark up where plates were going, and clean up the metal spotlessly with a grinder with a wire brush wheel.
3. dummy assemble the cage in the car with the mounting brackets and tack weld the brackets in the correct position
4. remove the cage, and get the brackets welded fully
5. paint the brackets/ surrounding area
6. reassemble the cage

I had to put a couple of small spacers in where the main hoop bolts to the roof, as when I checked on first assembly, i'd pulled the roof down a bit - doh! sprung back though !

Hope that helps - even if not how to do it

[drjim]

Well I've got the cage in for its initial fit, will be removed for painting of cage/interior in due course. Used the 2mm plate that came with the cage, plus some bigger pieces of 3mm to level things out where the car floor was shall we say "non OEM"

I have started fitting the seats (cheapie Cobra non stickered buckets - trackday car only), which is going to involve grinding out the supports for the original seats and bolting direct to the floor - via some box section between seat and floor, and some 3mm plates under the floor.

Now my next question relates to door bars. The cage comes with brackets to be welded on to the front and B pillar cage bars, and has door bars to be cut to length and the end fitting welded on. I will get the seat mounting (and pedal box location) sorted first, and was thinking that the door bars should be fitted at around the level of my hips - is this correct??

[Notso Swift]

That is a bloody good place to start!

I presume it is a single not a cross type?

Honestly a little above is best, because you can protect torso and hip. and run it lower at the front. If it is a cross type then get it iup to rib cage height, the lower cross protects the hip.

On thing I cannot recommend enough is a bar at teh base of the main hoop running from one side to the other, in a T bone those door bars are pretty much useles if the rest of the the thing collapses in.

[JohnD]

Drjim,
Your door bars are to be welded in?
Consider the advice in the MSA Blue Book ( C9c) Competitors safety, para 25) about the embrittling effect of excess heat on the steel used for roll cages. Get a pro-welder to do the job, rather than DiY?

Also the section on door bars, C(c) para 20: "...may be removeable". So a suitable fixing clamp is acceptable without welding. Also, "The side protection must be as high as possible but not more than one half of the total height of the door aperture measured from its base."

John