CSL bodyshell stress crack - warning!

Hi Folks

At the end of last season at the ring, the mechanic I use at the ring (Tom Schirmer) noticed a small stress crack on the bodyshell, right beside the front subframe mount. He told me he's only seen it a few times before, and he's seen quite a few CSLs that get worked hard. We didn't have time to fix it then (I was returning home) but it needs fixed before any more track work he reckoned.

Anyway, we finally got the car on the ramps today (back in Scotland) and took off the whole rear axle:



And after cleaning off the grime we could see the crack had got worse.



Luckily we've caught it in time though, we're welding the crack and then going to weld 4 plates on each subframe mount, that should stop it happening again.

My car gets a reasonable work out, but also I have fitted solid subframe mounts from Turner Motorsport about 2 years ago which obviously contributed to the stress crack on the bodyframe.

I thought I'd post this thread as a warning to anyone who's car gets some serious track work, and/or anyone who's upgraded their subframe mounts. Check for stress cracks regularly!

[SMD]

Cheers for the heads up mate!

Are you runing coilovers on the rear, is that the reason for this?

Originally Posted by SMD

Are you runing coilovers on the rear, is that the reason for this?

Yes, AST coilovers on the rear. But I'm also have a cage helping to stiffen the whole car, and I thought the problem with coilovers at the rear was the top mount cracking? I could be wrong. Anyway my coilovers have a reinforced top plate and it appears fine. I think it more likely the problem was caused by subframe has no give now its solid bushes? However I mention it here in case its a wider problem about to rear its head as these cars (and std e46 M3s) get older and more widely tracked.

[NZ_M3]

Oh oh ... this would be the first reported CSL with the infamous re-subframe mount crack/tear on the E46 Chassis ...

It's quite chronic with the normal E46 M3s (just do a search on American E46 M3 forums and you'd get hundreds of threads about it) ... but this is the first that I've seen one on a CSL .. .this is not good.

[Bealo]

This is the good thing about the forum, we will all learn together when we pass our findings on to eachother.

Thanks Steve.

[sailorbaz]

Cheers for the heads up Stevie. And here's me worrying about poxy bumper repairs, your cars cracking up! ;-)

All sorted now, still on the hunt for a corner piece but no rush.

[RichW]

Thanks for the heads up Steve - hope you get it sorted, will be keeping an on mine in the future, even though i've yet to track it

[glendog74]

That's not good! I've seen a few cars pass through Simpson MS that have those solid billet bushes and they are certainly a tad more extreme than poly bushes are over the OEM rubber versions!

It's not something i would consider as my car is also used loads on the road and surely that must make it ride hard? I'm not gonna worry about cracks on mine just yet but will keep a weather eye on that area - cheers...!

[bryce]

Originally Posted by NZ_M3

Oh oh ... this would be the first reported CSL with the infamous re-subframe mount crack/tear on the E46 Chassis ...

It's quite chronic with the normal E46 M3s (just do a search on American E46 M3 forums and you'd get hundreds of threads about it) ... but this is the first that I've seen one on a CSL .. .this is not good.

Was just gonna point that out. Loads of e46's doing it on the Yank forums. Seems to be a common problem

Heard of one getting his subframe replaced under good will. Was a 7yo car with lots of miles too.

[NZ_M3]

Originally Posted by bryce

Was just gonna point that out. Loads of e46's doing it on the Yank forums. Seems to be a common problem

Heard of one getting his subframe replaced under good will. Was a 7yo car with lots of miles too.

It happens a lot more to earlier cars - but according to the yanks there isn't really a trend or 'real reason' behind it other than under-design by BMW.

In 2005 the E46 rear subframe mount floor had an updated part number that was suppose combat this - to date there have still been cars from that era showing signs of cracks.

BMW did bring out a TIS bulletin of an injection foam to fix initial stress cracks like the one on Steve's car - I have the pdf file for it - but supposedly this is no longer available as a 'fix'


To date (until Steve posted this up) there have been no reported cases of CSLs doing this. I was hoping that it never would as I was hoping that weight would have something to do with this 'defect' (CSLs being light and all, and whilst it's a torque induced issue ... having a heavier car exacerbates such problems)

It is a torque induced stress in the body, which leads to mounting point cracks.

I've spoken to a learned BMW technician here locally and he's of the opinion that so long as you don't abuse the car and drive on perished bushes (on the rear end) then the likelihood of these stress cracks appearing will be considerably lowered.

I would suspect that the solid rear subframe mounts would have contributed to this some what.

Hopefully you get it sorted Steve - the Turners Rear subframe kit requires quite a bit of cutting in both the floor and boot to fit the kit ... there's been some merit put forward by the yanks that structural bonding (i.e. glue) might be the better alternative and prevent rust in the future (given that you can't rust proof the otherside of the metal that's been welded.