Unwanted Exhaust Mod

by Bimmerfest.com Member - rtgirard on February 11, 2013, 9:37 am
Unwanted Exhaust Mod, Or: How I learned to stop worrying and love road salt

I'm a little surprised at the use of plain, old steel machine screws for holding the electric actuator in place for the exhaust flap. As you can imagine, mine have failed after 2500 miles and exposure to road salt for the past 3 months.

My wife returned home from errands on Saturday and I saw this:



The three screws that secure the motor housing to the bracket have sheared off... the remaining screw pieces are still in the bracket and are quite rusty.



The heads just broke right off, I assume. We found one of the three in the garage.



I did wire the flap open to keep it from rattling at idle. It was very, very loud. The wire and plug going to the actuator have been zip-tied up out of the way and protected from road dirt by electrical tape and a piece of a plastic shopping bag... all held well away from the pipes and muffler.

So, yea. Kinda depressing to know that no forethought was put into materials used on the car in the NA market. Despite how dirty the car is in the photos (it had just returned from playing in the remnants of Nemo), I generally keep the car pretty clean all winter, including rinsing the underside fairly well. I don't mean to imply that I keep it spotless, but I'm sure there are new 335s out there that stay far dirtier all winter than ours does.

Oh well. Appointment made. Hopefully they will replace the screws with something less susceptible to corrosion.

exhaust, flap, rattle, screws, corrosion, f30, 335i, road salt, actuator


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28 responses to Unwanted Exhaust Mod

SamS commented:
February 11, 2013, 9:53 am

Wow!

As a lifelong Texas resident, I am always shocked at the road conditions you guys go through and the potential impact on the undersides of these cars. Stuff like this (and looking at the underside of your car) would drive me absolutely nuts. I can't imagine taking a brand new $50K+ car through the muck you guys experience. If I ever have to move up north, I know for sure to get a winter beater now!
tim330i commented:
February 11, 2013, 2:25 pm

That is surprising, BMW does a lot of cold weather testing. I wonder if it is a one off issue or something we'll start seeing a lot of.

Tim
SD Z4MR commented:
February 11, 2013, 6:10 pm

Quote:
Originally Posted by tim330i View Post
That is surprising, BMW does a lot of cold weather testing. I wonder if it is a one off issue or something we'll start seeing a lot of.
Cold weather testing means nothing if the area that one is testing in doesn't use salt on the roads in winter. The only way they could test this would be to spray a salt solution on the undercarriage every day for months or years.

I grew up in Detroit in the 50's and 60's and lived there through the 80's. You didn't have to know how old a car was, you could probably tell by how much rust there was on the car. Underneath Detroit is one of the world's largest salt mines so it was a very cheap solution to icy roads in winter. I never owned a car there for more than 60,000 miles because I wanted to sell it before it rusted through.

Rust protection has improved a lot since then, but salt on the roads is still the enemy of cars. I don't miss it at all!
tim330i commented:
February 11, 2013, 6:12 pm

I just assume were there is snow they use salt on the roads.

Tim
rtgirard commented:
February 11, 2013, 8:34 pm

Well, hopefully it's just a fluke. 2500 miles and three months of cold/salty roads seems too short a time for something like this. Maybe the flap-motor-robot was loaded with the wrong screws back on September 24th when the car was assembled.
-=Hot|Ice=- commented:
February 11, 2013, 9:31 pm

They're just not built like they use to be.
SD Z4MR commented:
February 11, 2013, 10:38 pm

Quote:
Originally Posted by tim330i View Post
I just assume were there is snow they use salt on the roads.

Tim
Salt is not used everywhere there is snow, sand and other material is used in some places. There is a large salt mine in Germany in the Berchtesgaden area, but I've never driven in Europe in the winter so I can't say what they use there.
K-A commented:
February 13, 2013, 5:18 am

There's a rust problem (i.e lack of proper galvanization/corrosion prevention) in BMW's manufactured using the universal platform the F30 uses (i.e BMW's smaller cars). I've seen lots of pics of F30's and F20's with rust underneath seats, in the dash area (in HVAC vents, etc.), around the area that extends from the belt buckle, etc. Seems this issue can now be thrown into the mix.

For whatever reason, this is something that seems to have been either overlooked or cost cut (can't tell which is more alarming) in the smaller BMW cars coming out in this aspect. The larger cars that sit on the F01/F10/etc. shared platforms use different steel suppliers apparently and don't suffer such rust issues.
rtgirard commented:
February 13, 2013, 7:22 am

And... I'm not the only one: http://www.bimmerfest.com/forums/sho...d.php?t=676029
Mark K commented:
February 13, 2013, 4:33 pm

Quote:
Originally Posted by -=Hot|Ice=- View Post
They're just not built like they use to be.
We can blame BMW all we want (and in this particular case it might be appropriate), but this is no country for new BMWs. Most of it isn't. Where do we put blame for bent wheels, shattered windshields, broken front bumpers, baseball-sized hail damage, flood damage, dinged doors, first-in-line-to-get-a-ticket, a-holes road raging for nothing more than a legal pass on dotted two-lane road ... and on and on and on ... where do we put a blame for that?

We should all get the best vehicle to own in U.S. - beaten-up 7 years old pickup truck. Says a lot about our road transportation system, doesn't it?
Jamesonsviggen commented:
February 13, 2013, 4:40 pm

Quote:
Originally Posted by K-A View Post
There's a rust problem (i.e lack of proper galvanization/corrosion prevention) in BMW's manufactured using the universal platform the F30 uses (i.e BMW's smaller cars). I've seen lots of pics of F30's and F20's with rust underneath seats, in the dash area (in HVAC vents, etc.), around the area that extends from the belt buckle, etc. Seems this issue can now be thrown into the mix.

For whatever reason, this is something that seems to have been either overlooked or cost cut (can't tell which is more alarming) in the smaller BMW cars coming out in this aspect. The larger cars that sit on the F01/F10/etc. shared platforms use different steel suppliers apparently and don't suffer such rust issues.
The seat rust issue is due to supplier Lear not using a coating. They now are using the coating again lol.
K-A commented:
February 13, 2013, 5:34 pm

Quote:
Originally Posted by Jamesonsviggen View Post
The seat rust issue is due to supplier Lear not using a coating. They now are using the coating again lol.
Ahh, good to know. Glad that was taken care of (and was something as simple as a supplier issue rather than a cost-cutting or overlooked engineering defect).
Orient330iNYC commented:
February 13, 2013, 6:27 pm

tbh, it doesnt look like those bolts rusted through, they look like they are snapped off due to either overtorque at the factory, or defective materials.
op, does the bolt you have look sheared off? and are they steel or aluminum?
-=Hot|Ice=- commented:
February 13, 2013, 6:39 pm

Quote:
Originally Posted by Mark K View Post
We can blame BMW all we want (and in this particular case it might be appropriate), but this is no country for new BMWs. Most of it isn't. Where do we put blame for bent wheels, shattered windshields, broken front bumpers, baseball-sized hail damage, flood damage, dinged doors, first-in-line-to-get-a-ticket, a-holes road raging for nothing more than a legal pass on dotted two-lane road ... and on and on and on ... where do we put a blame for that?

We should all get the best vehicle to own in U.S. - beaten-up 7 years old pickup truck. Says a lot about our road transportation system, doesn't it?
That's no excuse because the 3 series cars sold in Germany are no different then the ones sold in the US, other then packing. In the US Market, they are considered to be 'Premium'(Not sure how much longer that's going to last with all these new models coming) but if I pay for a premium product, I expect it to be a premium product. BMW needs to tighten the quality control.
AndDown commented:
February 13, 2013, 11:12 pm

Quote:
Originally Posted by Orient330iNYC View Post
tbh, it doesnt look like those bolts rusted through, they look like they are snapped off due to either overtorque at the factory, or defective materials.
op, does the bolt you have look sheared off? and are they steel or aluminum?
Agree, it takes much longer for rust to weaken a bolt that size and for all three bolts to shear. Sounds like over-torque on bolts made with cheaper material. I looked under my car tonight and it looks amazingly clean (at 4000 miles), but then again, it doesn't rain much in S. Calif.
rtgirard commented:
February 14, 2013, 11:28 am

Quote:
Originally Posted by Orient330iNYC View Post
tbh, it doesnt look like those bolts rusted through, they look like they are snapped off due to either overtorque at the factory, or defective materials.
op, does the bolt you have look sheared off? and are they steel or aluminum?
I think it's steel and it does look sort of snapped... Not sure if the snap was caused by over torque or weakened state due to corrosion. The remaining pointy-end of the screws left in the bracket are very rusty.

I will attempt to post better pics of the screw tonight after I get home from work (will be late... Damn travel day).

Appointment with shop to get it fixed is tomorrow.
rtgirard commented:
February 14, 2013, 9:25 pm

Here's a photo of the break point. It looks to my untrained eye as if corrosion weakened it to the point of breaking under whatever remaining stress was on the screw after install.

Anyone with actual experience in materials engineering would obviously be a much better judge of what may have actually happened. I offer this photo evidence merely as fuel for further conjecture and entertainment. :-)

I'm heading to the dealer tomorrow. With luck, all I need are 3 corrosion resistant screws and to have my chicken wire removed from the flap pivot.
rtgirard commented:
February 14, 2013, 9:28 pm

Quote:
Originally Posted by AndDown View Post
Agree, it takes much longer for rust to weaken a bolt that size and for all three bolts to shear. Sounds like over-torque on bolts made with cheaper material. I looked under my car tonight and it looks amazingly clean (at 4000 miles), but then again, it doesn't rain much in S. Calif.
For giggles, can you reach up and grab the actuator body and give it a shake? I'm curious as to if yours is loose since you are lucky enough to have salt-free roads. Thx in advance!
AndDown commented:
February 14, 2013, 10:55 pm

Quote:
Originally Posted by rtgirard View Post
For giggles, can you reach up and grab the actuator body and give it a shake? I'm curious as to if yours is loose since you are lucky enough to have salt-free roads. Thx in advance!
Solid, no wiggles or looseness. I've taken a picture of mine for comparison. My manufacture date was 1st week of July, 2013.
Orient330iNYC commented:
February 14, 2013, 11:10 pm

Quote:
Originally Posted by rtgirard View Post
Here's a photo of the break point. It looks to my untrained eye as if corrosion weakened it to the point of breaking under whatever remaining stress was on the screw after install.

Anyone with actual experience in materials engineering would obviously be a much better judge of what may have actually happened. I offer this photo evidence merely as fuel for further conjecture and entertainment. :-)

I'm heading to the dealer tomorrow. With luck, all I need are 3 corrosion resistant screws and to have my chicken wire removed from the flap pivot.
looks like it was overtorqued-- you would need to rust through probably more than 1/3-1/2 the bolt to snap with just the force of the actuator operating , and the metal is clean (although sheared). the rust you see is superficial.

my guess is that the mufflers are assembled with the solenoid and the person or machine doing it has the torque set way too high. or a bad batch of bolts. my bet would be that there's a whole batch of these produced between X and Y date that will snap.
AndDown commented:
February 14, 2013, 11:15 pm

Quote:
Originally Posted by rtgirard View Post
Here's a photo of the break point. It looks to my untrained eye as if corrosion weakened it to the point of breaking under whatever remaining stress was on the screw after install.

Anyone with actual experience in materials engineering would obviously be a much better judge of what may have actually happened. I offer this photo evidence merely as fuel for further conjecture and entertainment. :-)

I'm heading to the dealer tomorrow. With luck, all I need are 3 corrosion resistant screws and to have my chicken wire removed from the flap pivot.
Looks like a shear failure, probably due to defective material and possibly excess torque. In your picture, it appears that the failure started at the 5 o'clock position of the bolt, and it seems there might be some foreign items at that area, possibly weakening that area. I'm not a materials engineer, but have done quite a bit of research studies on shear fracture. Does not appear that rust has penetrated into the bolt as far as I can tell. Also, looking at your pictures and comparing it with what I posted, the fracture site is not in an area exposed to the elements.
rtgirard commented:
February 15, 2013, 7:41 am

Hope you're both correct. I don't want to deal with this next February again.
vern commented:
February 15, 2013, 8:46 am

Quote:
Originally Posted by Orient330iNYC View Post
tbh, it doesnt look like those bolts rusted through, they look like they are snapped off due to either overtorque at the factory, or defective materials.
op, does the bolt you have look sheared off? and are they steel or aluminum?
+1 IMO it just doesn't seem that rust alone would snap those bolts in such a short period of time. I would say its a good bet tensile strength of the material had a lot to do with it. They could have been to hard and the stress contributed to the bolts snapping off. Rust alone,no way.
cheers
vern
rtgirard commented:
February 16, 2013, 8:48 am

Well, diagnosis is basically incomplete. I'm now awaiting a replacement actuator as they are afraid to put the same one back on the car. I probably won't get the old actuator back, so I won't get a chance to do a post mortem to see if it is the cause of extra stress on the screws.

The tech basically said, "Yep, they broke. They were very rusty on the bottom, but look like they sheared."
rtgirard commented:
February 20, 2013, 7:54 am

Final update: Obviously BMW took care of this under warranty and replaced the entire actuator, retaining clips and screws. The replacement screws are exactly the same... steel. Still no consensus on the root cause. I'm am, however, happy to have the car back without chicken wire holding the flap open.
BMRRR commented:
June 5, 2013, 8:39 pm

Re: Exhaust, flap, rattle, screws,

I have BMW 2013 335xi M-Sport with the same problem after only 7000 km (4350 mi).

That is not just salt!
I believe that is a galvanic corrosion of regular steel bolts against the stainless steel exhaust. That is a deadly combination for the regular steel bolts. They are just melt to dust very fast while in direct contact with a stainless steel part. Also, maybe some fatigue cycles are involved heavily too. That looks like a major design failure!
rtgirard commented:
June 6, 2013, 10:41 am

Quote:
Originally Posted by BMRRR View Post
Re: Exhaust, flap, rattle, screws,

I have BMW 2013 335xi M-Sport with the same problem after only 7000 km (4350 mi).

That is not just salt!
I believe that is a galvanic corrosion of regular steel bolts against the stainless steel exhaust. That is a deadly combination for the regular steel bolts. They are just melt to dust very fast while in direct contact with a stainless steel part. Also, maybe some fatigue cycles are involved heavily too. That looks like a major design failure!
Thanks for your update... when did you take delivery and do you know your production date?
AndDown commented:
June 7, 2013, 1:24 am

Quote:
Originally Posted by BMRRR View Post
Re: Exhaust, flap, rattle, screws,

I have BMW 2013 335xi M-Sport with the same problem after only 7000 km (4350 mi).

That is not just salt!
I believe that is a galvanic corrosion of regular steel bolts against the stainless steel exhaust. That is a deadly combination for the regular steel bolts. They are just melt to dust very fast while in direct contact with a stainless steel part. Also, maybe some fatigue cycles are involved heavily too. That looks like a major design failure!
Re-looking at the close-up picture of the fractured site posted by the OP (thread #18), it looks more like a shear-failure than a corrosion failure to me. Also, I'm not sure if the exhaust is stainless steel...someone else in the know needs to chime in on this. From looking at my unit (thread #20), the bolts are not fastened directly to the exhaust in any case, but to a bracket that has been welded to the exhaust.