Ian

M2 redux

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hi Ian

having seen a lot of cages and relied on them for protection in more than a few race cars...

are the bottoms of your tubes going to be welded directly to the car? looks like it from the pics, but maybe that is just a test fit. if so, kinda dangerous. they should be welded to a plate or box to spread the impact load to multiple planes of the unibody. using a box also makes getting the cage tight to the roof a lot easier. build the hoops 4in short, and then use box underneath to raise up to roof. weld box to car on multiple sides.

also curious why the lighter tubing in key impact zones. i would not use the lighter tube in door or foot well areas, i would trade safety for weight in those places.

nice project! i will be joining you in M2 land this fall. have S14 (actually an entire m2 with bad shell), putting in my 75.

Marshall

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Hi Marshal,

This is early on, so the reinforcing plates for the floor are not in place yet. I'll build a box for the front rockers, but weld the main hoop to reinforcements on the floor. To get the top welds I'll cut holes in the floor and drop the cage. After the top welds are done I'll raise the cage, insert the reinforcing plate, and weld the floor.

Good point about the door bars, they should have been .095 wall (blue). I've updated the pic to reflect the change.

It will be great to have another M2 in the bunch!

Ian

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ill try to get some pics of the cage mounting boxes in my 325 race car and post'em for you. whole cage was done on boxes. cage was built with boxes out so that top bars could be welded, then cage was raised and boxes welded in underneath. made for good welds and no cutting of floor. (I didn't do it, my welding skills suck...)

i would at least do the door x bars in the thicker tube.

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Since my car will also be driven on the street occasionally, I wanted to get the cage as high in the cockpit (away from my head) as I could. I had been told that rollbars marketed for 2002's without sunroofs were 1" taller than those for sunroof cars. This would allow me to move the A-pillar bars higher, thus away from the old noggin.

I checked this with a cage I made for a friend with a sunroof 2002. I built it snug to the headliner in my '76 sunroof car, then removed the headliner. There is a surprising amount of extra headroom above the bar. Allowing 1/4" for headliner and padding, there is an extra 2" of space above the bar I made snug to the sunroof headliner.

Cage_Clearance.jpg

So this weekend I performed a sunroof-ectomy on my car. This could also be thought of as the "sunroof delete" option for 1976. A little quality time with a 1/16" cut-off disc in my grinder resulted in this expanse of headroom.

Sunroof_Delete.jpg

I bent up a main hoop destined for another friend's non-sunroof 2002 racecar, and resulted in much more headroom for the old noggin.

After I get the cage sorted out I'll break out the oxyacetylene welder an put in a patch panel.

As long as I had the grinder with the cut-off disc out, I removed a section of the rear bulkhead to make planning the rear of the cage easier.

Rear_bulkhead.jpg.

I'm going to run braces from the main roll hoop to the rear shock towers, and between the shock towers and the differential. This view shows the relation between the main hoop and the rear shocktowers. While not necessary for installing a cage, removing this much of the bulkhead makes it easy to plan out the tubes. I'll put in a new bulkhead, with holes for the tubes, once all is done. This view also shows my custom motorsport laptop stand (the bucket on top of the gastank) ;)

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I had some time to work on the cage again, and got my doorbars roughed out. I have a tube running along the rocker between the A-pillar bar and the main hoop. Because the main hoop is just inboard of the rocker, while the A-pillar bar sits on top of the rocker, this rocker tube had to turn inward at the end to meet up with the main hoop. Intersecting the rocker bar at each end where it meets with the vertical bars is the curved lower door bar.

These door bars required some careful fishmouthing, but I think they came out nice. Some of the cuts were too steep to use my tube notcher, so I used a 4.5" angle-grinder setup with a 1/16" cut-off blade to cut the pattern, then smoothed it out with a carbide tip on a die grinder. After muscling the tubing around to get exact rotation and bend angles for the A-pillar bar, it was pleasant to do nothing more than make a single bend in some tube for a change.

I'm going to include two vertical bars on either side of the door bar intersection, and will make a gusset out of 18 ga steel over the weekend. The bars are tight to the door to give you room, but I'm going to have to change the angle of bend for my car, as the upper bar interferes with the window crank in this version. It means I can only roll the window up and down with the door open; not a problem in a race car, but not desirable on a dual-purpose car ;)

Doorbar_01.jpg

Doorbar_02.jpg

Doorbar_03.jpg

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Worked on the gussetts today. I wanted to box the intersection where the door bars join, but didn't want to have the added height on top, to make it easier to climb over the door bars. I settled on boxing the intersection on three sides, and made a gussett out of 18 ga steel.

I had some scrap 18 ga from another project. It had a work-hardened corner on the bottom, but I flipped it over and used it as a test piece anyway. I made the gussett out of one piece of sheet metal, and trimmed it to contour the top of the "X" of the door bars. I used the bars as hammerform to fold the tube over, and it will get welded down the seam on top, and along all the tubes. A couple of dimples added stiffness and bling, and I think I have a usable design.

Now to find some more 18 ga and make these for real.

gussett1.jpg

gussett2.jpg

gussett3.jpg

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Picked up some more 18 ga and made the gussets for the door bars. Here's an in-car test fit. These are actually for a friend's race car. I think for my car, where I need to use the window winders, I'll extend the low spot in the "X" forward to clear the handles. In this case the upper bar will actually look like this: \____/ instead of like this: \/. Admission: I'm copying this latter design from Woodstock; but hey, if it's good enough to win Targa, it's good enough for my car!

Gusset_in_car.jpg

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It looks great, Ian! The old girl will be really stiff and is built like a brick house. Hope to see you drive it with great earnestness some day at 10/10ths.

Mike

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Right now, I'd settle for 1/10 ;) I sat it in it yesterday and made "vroom-vroom" noises, does that count?

One track that is on my list to visit is Road Atlanta when the M2 is up and running again.

Ian

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One track that is on my list to visit is Road Atlanta when the M2 is up and running again.

Ian

Let me know when you come to Road ATL.. its 10 minutes from my house. Id love to meet you and see your car!

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One track that is on my list to visit is Road Atlanta when the M2 is up and running again.

Ian

Let me know when you come to Road ATL.. its 10 minutes from my house. Id love to meet you and see your car!

Definitely!

Disclaimer: It's not likely to be this summer or next, as my ability to estimate the time it takes to complete a task is notoriously poor, at least according to my wife ;)

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Man, it sounds like your car will be done a few years before mine :)

There's room at the RoachMotel for you guy(s). Come on down for a March, July or Sept CCA event (peachtreebmwcca.org). Friday offers up to 8 hrs of open track time and it's truly sublime. The Sept DE is usually a week away from the Petit LeMans weekend.

Keep it going, Ian!!

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Man, it sounds like your car will be done a few years before mine :)

There's room at the RoachMotel for you guy(s). Come on down for a March, July or Sept CCA event (peachtreebmwcca.org). Friday offers up to 8 hrs of open track time and it's truly sublime. The Sept DE is usually a week away from the Petit LeMans weekend.

Keep it going, Ian!!

That sounds great. Perhaps I could trade some M2 motor mounts for hospitality! The only kink in the plan is that I seem to remember that with those accommodations, you can check in but never check out ;)

Ian

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Worked on the cage some more. While I really like the doorbars with gusset for a race car, I don't think they would be that good for a street car, even if I lowered the height of the saddle. In addition, the door bars are very tight to passengers if they are arranged to clear the interior door panels and handles. Not a problem with a race car where you don't care about the handles and can orient the door bars a little farther outboard for clearance. In fact, I have been told that setting up the door bars with a slight outward deflection is a good thing, as in a side collision the door bars will be bent inward into compression and resist the force. If the bars are set up dead vertical, then a side impact will put them into tension, which will depend on the welds to hold the door bars intact under tension.

So, for a variety of reasons I think I'm back to doing a single diagonal for the door bar. I can get clearance for my seat, make entry easier, and still get some triangulation between the bottom of the A-pillar bar and the main hoop. The trade-off is less side protection, but this is not a concern for me, as this car is for lapping days and weekend driving, not door-to-door racing.

doorbar_street.jpg

I've also finished the first cage in a set of cages I contracted to build. To help defray some of my own costs, I offered to make custom cages for fellow 2002 fanatics, and had four takers for the first batch. Since I've developed these designs in BendTechPro software, and have a digital readout for my tube bender, I can recreate most of the design features I've worked out for my cage and for these initial designs. Right now I've finished a 2002 (non-sunroof, race car), almost finished a second 2002 (sunroof street/rally car), have measurements for a CS racecar, and interest in a second 2002 race car. And then I get to start my own cage ;)

Anyone else for a "Roll Cage in a Box"? They can be either 1.5" or 1.75" DOM. Here is the first cage, just about ready for shipping. All the tubes are bent, labeled, notched and about .25" long to allow for car-to-car variation.

cage_in_a_box.jpg

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