My Understanding of the M Rear Beam

[Pingu]

 

[deano1712]

Hey. Is the strengthening the only difference with the M/non-M. Geometry the same?

Adding steel to the outside will be effective probably more so than that odd internal piece. Did you consider straigthening the old beam? You could have tried my press.

 

[Peter1450]

Would this have the same effect as the weld on kits I’ve seen online that the drift guys are using?

 

[Stevo7682]

Gary does the standard non m car beam definitely not have the additional internal brace.
Obviously you have cut open a damaged one. I take it m beam hes different part number from say a 2.8/ 3.0 one.
I can totally understand that it would be beefed up as the original was never designed to run with the forces the m power plant provides.
Stephen.

 

[Pingu]

Hey. Is the strengthening the only difference with the M/non-M. Geometry the same?

Adding steel to the outside will be effective probably more so than that odd internal piece. Did you consider straigthening the old beam? You could have tried my press.

I've got a 12 ton press, but I don't think that would touch it. The beam was twisted rather than bent. I cut the beam and I did consider welding it back together, but this time straight. I abandoned that thought after about 10 seconds.

I've decided to "do a Randy" and just throw metal at it .

I have done some man-maths and have worked out that I can replicate the resultant force using the two perpendicular vector forces if I weld metal to the three sides of the lower section. See below. I'll be using 3mm steel instead of the 2mm that they used.

The lower section will be one piece of steel, not two. The illustration just shows what I think is needed to replicate the two 2mm pieces, but using 3mm steel.

I've made a start and have welded the lower section to the beam, and it looks like it can be done.

I'll also be adding camber and toes adjustment plates to the rear arm supports.

The dimensions are the same for both beams as far as I can tell. The only external difference is that the M-beam has an exhaust bracket on both sides. The standard beam only has the bracket on the left side.

 

[Pingu]

Gary does the standard non m car beam definitely not have the additional internal brace.
Obviously you have cut open a damaged one. I take it m beam hes different part number from say a 2.8/ 3.0 one.
I can totally understand that it would be beefed up as the original was never designed to run with the forces the m power plant provides.
Stephen.

Standard beam has no internal reinforcement that I can see. The reinforcement on the M-beam is visible through the drain hole, but I also had a look using a boroscope to see where to cut the beam.

The standard beam is used on all models of E30 and E36, except the Ms.

The E30 M3 has a unique rear beam. I suspect that it has reinfocement, but only one exhaust bracket.

 

[Stevo7682]

Knowing you i thought you would have properly investigated it.
I was just trying to glean some more information on the subject as it is always good to know this stuff.
I take it the arm mounts on the beam are in the same position on m and non m beams and its just the arms themselves that are different.
Thanks Stephen.

 

[Pingu]

Knowing you i thought you would have properly investigated it.
I was just trying to glean some more information on the subject as it is always good to know this stuff.
I take it the arm mounts on the beam are in the same position on m and non m beams and its just the arms themselves that are different.
Thanks Stephen.

Yes, everything looks the same - and I've had my M arms bolted to the beam, so it all fits together.

It's probably not necessary to beef up the beam, but I thought I'd better - just incase I get the urge to give it the beans

 

[IainP]

Cheers for all that Pingu, I think I’ll redo mine with one of my spare beams, I do tend to break things.

 

[Pingu]

Cheers for all that Pingu, I think I’ll redo mine with one of my spare beams, I do tend to break things.

If you wait a few weeks, you will be able to see what I do, and take it from there.

 

[IainP]

Already planned on some of my scrap steel, either 50mm box split and dimple’d, or 45mm cds split up the middle. Possibly a cradle between the two, cardboard aided design this weekend.

 

[Stevo7682]

@Pingu
Gary was thinking about this last night @Delk would be a guy to speak to about the durability of the stock beam.
His car started as a stock 2.8 dont know if Delk has done any mods to his beam he would be able to tell you but his turbocharged 2.8 is putting out 100bhp more than your M is .
Stephen.

 

[Pingu]

@Pingu
Gary was thinking about this last night @Delk would be a guy to speak to about the durability of the stock beam.
His car started as a stock 2.8 dont know if Delk has done any mods to his beam he would be able to tell you but his turbocharged 2.8 is putting out 100bhp more than your M is .
Stephen.

Honestly, I don't think it is necessary to strengthen the beam. The additional strengthening inside is so marginal that it probably only adds a few percent to the strength.

I don't think it was a case of the M would break / distort a standard beam. I think the factor of safety was probably below the accepted level. and BMW were just covering their asses.

This next bit isn't for you, Steve, it's to help me confirm in my mind what's going on...

It's not the power that breaks things, it's the torque. If the wheels are turning, lots of that torque has been released. It's only the unreleased torque that will damage the car. That's why the worst case scenario is at max torque (engine rpm = 5000) just before the tyres lose grip on a standing start.

There is a really good picture of a Z3 at Sata Pod where the rear bumper is almost touching the ground at the launch. I can't find the image, but here's a video. Note how the rear dips just before the launch and also on the gear change...

 

[Delk]

I have raised poly mounts and weld in camber correction plates on my rear beam. Other then that its stock. I am running a little over 400hp with matching torque numbers. So far fingers crossed no problems even though it gets lauched quite hard. On a few occasions where the road condtions havnt been the best I have ended up with pretty bad wheel hop in first to the point I thought the CV shafts were coming out. Because of this I have bearings and parts for the diff and spare CV shafts in the garage.

 

[Duncodin]

Isn't there some strengthening in the floor and chassis box section too? There was an episode of wheelerdealers where they were doing a z3. Wotsis name (the tall one) welded in an additional layer of steel to that box section.

 

[Pingu]

Isn't there some strengthening in the floor and chassis box section too? There was an episode of wheelerdealers where they were doing a z3. Wotsis name (the tall one) welded in an additional layer of steel to that box section.

I have, but not as standard.

The floor IS a weak point - and it is well documented.

I'm pretty confident that I'm doing a lot of work for no good reason - other than to practise my welding