Exhaust flap

gunsmoker · 08-26-2023, 04:13 PM

One of the flaps on my exhaust is making a lot of noise at cold start when closed. I bought the bow clips to replace them, but when I removed the flap actuator, there was no bow clip. There was a different part instead and for the life of me I could not find it in any diagrams or online part stores I checked.
The part looks like a little bell or a bullet casing if you will. On one side it has a tiny rod across that mates with the actuator flap groove and on the other side it has some welded insert that has a cut where the flap axle goes. The rod and the cut on the other side are perpendicular. For the flap that makes noise, the rod and the cut are not entirely perpendicular, say 80 degrees, and that prevents the actuator from applying pressure to keep the flap fully closed, hence the rattle. Not sure if this has always been this way on my car and I just noticed it. I don't see how this part would bend or wear.

I'm looking to buy this part because it can't be repaired. Does anyone know what the part number for it is? Since this is not shown on the assembly diagram, I'm very much afraid if I call the dealership, they will tell me it's part of the muffler assembly, cough $1200, please. The other option is to see if I can somehow fit the bow clip in its place, but with the clip the the actuator groove and the flap axle are supposed to be parallel.
My F80 is a 2016 base model.

E92Roni · 08-26-2023, 08:08 PM

I was dealing with the same issue. Under load the car sounded like a can of marbles because the actuator was broken and the flap would stay closed. I ended up just taking out the whole module and jamming the valve open

tjkafka · 10-30-2023, 01:31 PM

Hello, bumping this thread as I am running into a similar issue. From all my research, in fixing an exhaust rattle, many suggest to start by replacing the "fixing bow" on the exhaust flap actuator, however when I look at my flap actuators, it seems that our M3's don't have the same "fixing bow" as gunsmoker has mentioned in his opening comments. I took pictures of mine to show, see attached.

Is there a reason why our actuators are different (and don't have the fixing bows like others I've seen doing this repair) and what parts would actually be needed for our cars to perform this fix?

Thanks!

gunsmoker · 10-31-2023, 08:45 PM

I ended up replacing the actuator. It's a motor with gears and I presume a gear had lost a tooth and it could not hold the flap tight in place. After playing with this, I think the motor is self-aligning. The way it works is that to get flipped in one direction or the other, it gets a pulse, starts spinning the gears in that direction and stops when it hits the flap motion limit. The pulse is long enough to get it there. When you try to install an actuator that has gone over one of the end positions (e.g. a brand new one), you may find it impossible to fit it into the assembly or might risk breaking the gears. The way to sort this out I came up with is this. Connect the actuator without mounting it and flip the control to open or close the flaps (say, with ignition on, set to sport mode and press the accelerator pedal to open the flaps). Then unplug the actuator and set the control to the opposite position (set to efficient mode to close the flaps). Then briefly touch the plug to the actuator to produce a shorter pulse to get it going in the opposite direction. This way it will stop moving halfway through and you will be able to fit it in the assembly and then plug it.

gunsmoker · 10-31-2023, 08:48 PM

tjkafka, the fixing bow is only used for the other type of exhaust assembly and it's not applicable to the barrel type. In this case the actuator is the rattle cause.

tjkafka · 11-01-2023, 07:50 AM

Gunsmoker - Thanks for the updates! A couple of questions for you, if I may:

1) Most importantly, did this fix your rattle issue?

2) Is this a different actuator than the one that uses the fixing bow? Can you tell me what the part number is and where you bought your actuator?

3) This method that you used to align the actuator to fit into the assembly, is this something you read about somewhere or you just figured out on your own (trial/error)?

4) Lastly, out of curiosity -- I've only ever seen others talk about the fixing bow type, but have been unable to find any information on this "barrel type". Do all other F models use the fixing bow type, but for some reason the M's use the barrel type? Wondered if you've learned anything on this topic.

Thanks!

gunsmoker · 11-01-2023, 11:30 AM

Changing the actuator did fix the issue. I bought it from Turner Motorsport, oem part number 18307851568. Just like you, before I got under the car, I read about the bow fix and bought that part just to see later that it was not relevant. I gather some F8x cars have the bow fix and some have the barrels. The actuator appears to be the same. What is different is the exhaust muffler. On our cars the flat end of the flap axle is purpendicular to the acruator axle groove and for the other cars these are parallel. The barrel approach seems more robust imo. With regards to the installation procedure, I came up with that on my own.

tjkafka · 11-01-2023, 02:20 PM

Gunsmoker - thanks for the quick reply/clarification. Awesome to hear that fixed your issue.

What was it that you saw that helped you determine that the actuator was the issue and needed replacement, in your case? I'm going to be unbolting mine this weekend and trying to know what to look for.

Thanks!

gunsmoker · 11-01-2023, 07:56 PM

Now that I know how this works, there is nothing else than the actuator in this assembly that can cause the rattle. Unlike the bow fix assembly, the barrel is not a flexible item that can degrade over time. If you don't believe me and if you have the rattle on one side only, like in my case, just swap the actuators and the problem will move.
When I first looked into this problem, I had 3 observations:
1. In the assembled state, I could touch the barrel and feel that it was a little loose on the side that had the problem. I felt I should stretch the spring a bit to help it.
2. I tried turning the actuator by hand after taking it off the exhaust and it felt that it skipped a bit. It's hard to turn it by design and you should not force it, but having broken teeth in the gearbox would cause exactly that. I didn't think much of it at the time.
3. The slit in the barrel was not exactly perpendicular to the rod and I felt that that was preventing the flap from closing tightly. I was also erroneously thinking at the time that this was a stepper motor that was being turned an exact number of steps and if at the last step the flap was not completely pushing against its frame, it would rattle. I couldn't explain what could cause a wear for the rattle to occur at that time - the barrel is a solid piece of steel. Nevertheless, I erroneously blamed it on the barrel and tried to find a replacement. The reality is that the barrel does not exist as a separate part number and is part of the muffler. I called my BMW dealer, checked at websites - nothing. Someone mentioned in a related thread here that I could ask an aftermarket vendor for that part and they would be kind enough to provide one. Instead, I built a barrel myself. Not as sturdy as the steel one - I used a 1" copper fitting and a cap for it from Home Depot, drilled a slit and used a screw for a rod. Aligned them such that the flap would be pushed harder towards its frame when closed. That made it better, but did not solve the problem completely. Then I swapped the actuators and I saw the problem move, recalled that the bad one skipped when I tried to turn it, bought a new actuator, put everything together including the original barrel and everything is functioning as intended.

gunsmoker · 11-01-2023, 08:07 PM

I realized you had not seen what the barrel looks like since you have not dismantled the assembly yet. It's a 1" steel cylinder that has a pin/rod across on one side and that's what fits into the groove of the actuator axle. On the other side the barrel has a welded indented cap with a slit in it where the flat end of the flap axle fits. I wish I had a picture.

tjkafka · 11-02-2023, 03:33 PM

Gunsmoker, this is suuuuuper helpful (and detail), much appreciated! I like the idea of swapping the motors to try to determine if it is the actuator itself, great suggestion - I am going to try that first.

Enzian · 02-18-2024, 01:44 AM

Gunsmoker, My MPE started to rattle and i have pin pointed it to one side. The bullet case feels lose. It's rattles on cold start until in put in sport it goes away. However, when Rev around 2k rpm i can hear the rattle.

Example of what I have: not my video.
https://youtube.com/shorts/LuCAH7fIf...EEGxa9-8z0ckMN

If I replace the actuator portion do you think that would fix it? I have two extra from my zcp that I will try.

Really appreciate this post and bump. I am sure this will help people out.

gunsmoker · 02-18-2024, 09:53 AM

crustaceans, yes, replacing the actuator will likely solve the problem. Please see post #4 on how to align the actuator with the barrel to be able to assemble it all together. Replacing the actuator is a 10min job if you have easy access. I had ramps to raise the back end of my car.

08-26-2023, 04:13 PM	#1
gunsmoker Second Lieutenant 282 Rep 275 Posts Drives: 2016 M3 Join Date: Feb 2018 Location: Mansfield, MA iTrader: (1)	Exhaust flap One of the flaps on my exhaust is making a lot of noise at cold start when closed. I bought the bow clips to replace them, but when I removed the flap actuator, there was no bow clip. There was a different part instead and for the life of me I could not find it in any diagrams or online part stores I checked. The part looks like a little bell or a bullet casing if you will. On one side it has a tiny rod across that mates with the actuator flap groove and on the other side it has some welded insert that has a cut where the flap axle goes. The rod and the cut on the other side are perpendicular. For the flap that makes noise, the rod and the cut are not entirely perpendicular, say 80 degrees, and that prevents the actuator from applying pressure to keep the flap fully closed, hence the rattle. Not sure if this has always been this way on my car and I just noticed it. I don't see how this part would bend or wear. I'm looking to buy this part because it can't be repaired. Does anyone know what the part number for it is? Since this is not shown on the assembly diagram, I'm very much afraid if I call the dealership, they will tell me it's part of the muffler assembly, cough $1200, please. The other option is to see if I can somehow fit the bow clip in its place, but with the clip the the actuator groove and the flap axle are supposed to be parallel. My F80 is a 2016 base model.
	Appreciate 1 Enzian117.50 Tweet Quote

08-26-2023, 08:08 PM	#2
E92Roni Second Lieutenant 159 Rep 257 Posts Drives: 2015 M4 2012 M3 1999 328IS Join Date: Nov 2018 Location: Los Angeles, CA iTrader: (0)	I was dealing with the same issue. Under load the car sounded like a can of marbles because the actuator was broken and the flap would stay closed. I ended up just taking out the whole module and jamming the valve open
	Appreciate 1 Enzian117.50 Quote

10-30-2023, 01:31 PM	#3
tjkafka Registered 2 Rep 4 Posts Drives: F80 M3 Join Date: Apr 2022 Location: NJ iTrader: (0)	Hello, bumping this thread as I am running into a similar issue. From all my research, in fixing an exhaust rattle, many suggest to start by replacing the "fixing bow" on the exhaust flap actuator, however when I look at my flap actuators, it seems that our M3's don't have the same "fixing bow" as gunsmoker has mentioned in his opening comments. I took pictures of mine to show, see attached. Is there a reason why our actuators are different (and don't have the fixing bows like others I've seen doing this repair) and what parts would actually be needed for our cars to perform this fix? Thanks! Attached Images Last edited by tjkafka; 10-30-2023 at 01:33 PM.. Reason: trying to attach images
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10-31-2023, 08:48 PM	#5
gunsmoker Second Lieutenant 282 Rep 275 Posts Drives: 2016 M3 Join Date: Feb 2018 Location: Mansfield, MA iTrader: (1)	tjkafka, the fixing bow is only used for the other type of exhaust assembly and it's not applicable to the barrel type. In this case the actuator is the rattle cause.
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11-01-2023, 07:50 AM	#6
tjkafka Registered 2 Rep 4 Posts Drives: F80 M3 Join Date: Apr 2022 Location: NJ iTrader: (0)	Gunsmoker - Thanks for the updates! A couple of questions for you, if I may: 1) Most importantly, did this fix your rattle issue? 2) Is this a different actuator than the one that uses the fixing bow? Can you tell me what the part number is and where you bought your actuator? 3) This method that you used to align the actuator to fit into the assembly, is this something you read about somewhere or you just figured out on your own (trial/error)? 4) Lastly, out of curiosity -- I've only ever seen others talk about the fixing bow type, but have been unable to find any information on this "barrel type". Do all other F models use the fixing bow type, but for some reason the M's use the barrel type? Wondered if you've learned anything on this topic. Thanks!
	Appreciate 1 Enzian117.50 Quote

10-31-2023, 08:45 PM	#4
gunsmoker Second Lieutenant 282 Rep 275 Posts Drives: 2016 M3 Join Date: Feb 2018 Location: Mansfield, MA iTrader: (1)	I ended up replacing the actuator. It's a motor with gears and I presume a gear had lost a tooth and it could not hold the flap tight in place. After playing with this, I think the motor is self-aligning. The way it works is that to get flipped in one direction or the other, it gets a pulse, starts spinning the gears in that direction and stops when it hits the flap motion limit. The pulse is long enough to get it there. When you try to install an actuator that has gone over one of the end positions (e.g. a brand new one), you may find it impossible to fit it into the assembly or might risk breaking the gears. The way to sort this out I came up with is this. Connect the actuator without mounting it and flip the control to open or close the flaps (say, with ignition on, set to sport mode and press the accelerator pedal to open the flaps). Then unplug the actuator and set the control to the opposite position (set to efficient mode to close the flaps). Then briefly touch the plug to the actuator to produce a shorter pulse to get it going in the opposite direction. This way it will stop moving halfway through and you will be able to fit it in the assembly and then plug it.
	Appreciate 0 Quote

11-01-2023, 11:30 AM	#7
gunsmoker Second Lieutenant 282 Rep 275 Posts Drives: 2016 M3 Join Date: Feb 2018 Location: Mansfield, MA iTrader: (1)	Changing the actuator did fix the issue. I bought it from Turner Motorsport, oem part number 18307851568. Just like you, before I got under the car, I read about the bow fix and bought that part just to see later that it was not relevant. I gather some F8x cars have the bow fix and some have the barrels. The actuator appears to be the same. What is different is the exhaust muffler. On our cars the flat end of the flap axle is purpendicular to the acruator axle groove and for the other cars these are parallel. The barrel approach seems more robust imo. With regards to the installation procedure, I came up with that on my own.
	Appreciate 0 Quote

11-01-2023, 02:20 PM	#8
tjkafka Registered 2 Rep 4 Posts Drives: F80 M3 Join Date: Apr 2022 Location: NJ iTrader: (0)	Gunsmoker - thanks for the quick reply/clarification. Awesome to hear that fixed your issue. What was it that you saw that helped you determine that the actuator was the issue and needed replacement, in your case? I'm going to be unbolting mine this weekend and trying to know what to look for. Thanks!
	Appreciate 0 Quote

11-01-2023, 07:56 PM	#9
gunsmoker Second Lieutenant 282 Rep 275 Posts Drives: 2016 M3 Join Date: Feb 2018 Location: Mansfield, MA iTrader: (1)	Now that I know how this works, there is nothing else than the actuator in this assembly that can cause the rattle. Unlike the bow fix assembly, the barrel is not a flexible item that can degrade over time. If you don't believe me and if you have the rattle on one side only, like in my case, just swap the actuators and the problem will move. When I first looked into this problem, I had 3 observations: 1. In the assembled state, I could touch the barrel and feel that it was a little loose on the side that had the problem. I felt I should stretch the spring a bit to help it. 2. I tried turning the actuator by hand after taking it off the exhaust and it felt that it skipped a bit. It's hard to turn it by design and you should not force it, but having broken teeth in the gearbox would cause exactly that. I didn't think much of it at the time. 3. The slit in the barrel was not exactly perpendicular to the rod and I felt that that was preventing the flap from closing tightly. I was also erroneously thinking at the time that this was a stepper motor that was being turned an exact number of steps and if at the last step the flap was not completely pushing against its frame, it would rattle. I couldn't explain what could cause a wear for the rattle to occur at that time - the barrel is a solid piece of steel. Nevertheless, I erroneously blamed it on the barrel and tried to find a replacement. The reality is that the barrel does not exist as a separate part number and is part of the muffler. I called my BMW dealer, checked at websites - nothing. Someone mentioned in a related thread here that I could ask an aftermarket vendor for that part and they would be kind enough to provide one. Instead, I built a barrel myself. Not as sturdy as the steel one - I used a 1" copper fitting and a cap for it from Home Depot, drilled a slit and used a screw for a rod. Aligned them such that the flap would be pushed harder towards its frame when closed. That made it better, but did not solve the problem completely. Then I swapped the actuators and I saw the problem move, recalled that the bad one skipped when I tried to turn it, bought a new actuator, put everything together including the original barrel and everything is functioning as intended.
	Appreciate 0 Quote

11-01-2023, 08:07 PM	#10
gunsmoker Second Lieutenant 282 Rep 275 Posts Drives: 2016 M3 Join Date: Feb 2018 Location: Mansfield, MA iTrader: (1)	I realized you had not seen what the barrel looks like since you have not dismantled the assembly yet. It's a 1" steel cylinder that has a pin/rod across on one side and that's what fits into the groove of the actuator axle. On the other side the barrel has a welded indented cap with a slit in it where the flat end of the flap axle fits. I wish I had a picture.
	Appreciate 0 Quote

11-02-2023, 03:33 PM	#11
tjkafka Registered 2 Rep 4 Posts Drives: F80 M3 Join Date: Apr 2022 Location: NJ iTrader: (0)	Gunsmoker, this is suuuuuper helpful (and detail), much appreciated! I like the idea of swapping the motors to try to determine if it is the actuator itself, great suggestion - I am going to try that first.
	Appreciate 0 Quote

02-18-2024, 01:44 AM	#12
Enzian Private First Class 118 Rep 112 Posts Drives: BMW i4 4p Join Date: Mar 2019 Location: Santa clarita, CA iTrader: (1) Garage List 2018 BMW M3 Comp [9.79]	Gunsmoker, My MPE started to rattle and i have pin pointed it to one side. The bullet case feels lose. It's rattles on cold start until in put in sport it goes away. However, when Rev around 2k rpm i can hear the rattle. Example of what I have: not my video. https://youtube.com/shorts/LuCAH7fIf...EEGxa9-8z0ckMN If I replace the actuator portion do you think that would fix it? I have two extra from my zcp that I will try. Really appreciate this post and bump. I am sure this will help people out.
	Appreciate 0 Quote

02-18-2024, 09:53 AM	#13
gunsmoker Second Lieutenant 282 Rep 275 Posts Drives: 2016 M3 Join Date: Feb 2018 Location: Mansfield, MA iTrader: (1)	crustaceans, yes, replacing the actuator will likely solve the problem. Please see post #4 on how to align the actuator with the barrel to be able to assemble it all together. Replacing the actuator is a 10min job if you have easy access. I had ramps to raise the back end of my car.
	Appreciate 0 Quote