I finally got around to it

[Randyjaco]

My 17 RT has had some issues (i.e. wimpy at high speed and poor gas mileage) I have discussed before. Several folks have suggested that the source might be the exhaust flapper valve. For unknown reasons I have avoided dealing with it. I was considering getting the ecu remapped. The fellow I was talking with suggested that I eliminate the flapper valve. I had some spare time this week, so I watched some videos and decided to give it a look. In order to not create more issues I decided to remove the butterfly.  The butterfly is essentially a circular disk welded to a shaft. The videos I watched were of  earlier models and mine was much more difficult to access. With a long nosed die grinder I was able to get the burr to the appropriate location. With about 30 minutes of grinding I was able to remove the butterfly.  I will have to say that the process was a real PITA. After putting everything back together, I went for a long ride. 

I was amazed at the increase in power between 4k-6k RPM's. No hint of wimpyness! The big surprise was my mileage went up by 4 MPG

I don't know what that flapper is supposed to do, but my bike runs much better without it. 

[Geekmaster]

Excellent, and thanks for the update Randyjaco.  I never understood why there is a flapper in the exhaust either.  I would think that for other than idle speeds, it would need to be fully open anyway.  And at idle speeds, what is the benefit of restricting the exhaust?

[Oldrider51]

I read that the flapper I is there to reduce noise, don't know how true, but several have replaced the section containing the flapper to a open pipe. Also, you can remove the servo motor and replace it with the Servo  Buddy so that you don't get any error codes. Have done this with my 16 R1200RS, but I have full Akrapovic system.

 

 

[mos]

So what does the exhaust flapper do ? Any benefits of it ?

[dirtrider]

2 hours ago, mos said:

So what does the exhaust flapper do ? Any benefits of it ?

Mornings Mos

 

It's main function is to reduce exhaust noise for noise emission compliance (big European concern) as it allows exhaust noise control in the RPM/engine load ranges that need modulation without using an over-restrictive muffler.  

 

It can also have a secondary usage of tuning the exhaust system for less reversion. 

[MichiganBob]

Top of the day DR. What does "tuning the exhaust system for less reversion" mean?                                                              "

[dirtrider]

3 hours ago, MichiganBob said:

Top of the day DR. What does "tuning the exhaust system for less reversion" mean?                                                              "

Afternoon Bob

 

Have you ever quickly turned off a water faucet then heard (or felt) a thump/thump/thump, or snap/snap/snap in the pipes? (or similar). 

 

That is the column of water in the pipes sudden reaction to a flow disruption or sudden change in backpressure. (think of the water column in the pipes as a standing wave) 

 

Same with the exhaust gas exiting the muffler or pipe. The sudden change of pressure (backpressure) as it exits to atmosphere causes the standing wave to snap back into the exhaust system & that can push spent exhaust gas back towards the exhaust valve.

 

On the BMW boxer engines you can sometimes see this reversion working if you allow the engine to idle, then hold a loose shop rag just behind the muffler outlet.  The rag will usually just flutter in cadence with the exhaust pulse then every once in a while it will suddenly get sucked right back against the muffler outlet, or even back into the muffler outlet (THAT is the reversion pulse at work ) 

 

In some applications this reversion (or reverse wave) can be used to add power or sort of act as a supercharger. Remember the old  (or even new) 2 stroke motorcycles that had that funny looking exhaust (looked like 2 funnels with a larger diameter pipe between them?

 

That is (in a nutshell) a diverging cone, converging cone, chamber, & a stinger. These can all be tuned for a specific RPM range to increase engine power. When the exhaust pulse reaches the end on the stinger it snaps (just like closing a valve), that sends a standing wave back into the expansion chamber (where it is re-focused back up the exhaust pipe. If it is tuned correctly that reverse (negative wave)  reaches the exhaust port JUST before the piston closes the port therefore pushing the slug of fuel/air that has been pulled completely through the combustion chamber (after combustion is over) back into the combustion chamber.

 

Forcing that short slug of combustible fuel/air back into the combustion chamber AFTER the piston has closed the intake side but just before it closes the exhaust side adds more combustible mixture to the next combustion process (somewhat like a supercharger would on the intake side). 

 

LOTS of variables in this so it isn't an easy thing to guess at but if tuned correctly can add a lot of extra power to the engine in a narrow operating range, it can also make the engine run like crap in other operating ranges. 

 

Have you ever heard the term "on the pipe"? That is when the exhaust tuning starts doing it's thing & you can definitely feel & hear that when riding a well tuned 2 stroke.  

 

In normal 4 stroke street type vehicles most of the reversion is stopped or killed by the muffler baffles & the catalytic converter so it usually isn't a big issue in full factory exhaust motorcycles. It can be an issue when a free-flow muffler is added & the cat removed though. 

[LAF]

Good job on the flapper removal. 

 

If I had not bought Akra headers I may have tried that.

 

I run a Servo Buddy and it passes the flapper test using a GS 911 so they work no muss no fuss.

 

The flap is noise abatement to meet Euro 5 standards and that is it.  With the new Akra headers and a Remus 8 exhaust my bike is louder on start but once underway it is only loud if I jump on it hard.  Shifting normally at sane RPM it is just a bit louder but the sound and tone is really nice to my ears.  And to add my bike is dyno tuned with a PC V so my fuel is right for the exhaust and that makes all the difference. 

 

However removing the flap IMHO will not affect exhaust or performance one bit.

 

Better gas mileage sounds good though.

[MichiganBob]

Good day DR. That's interesting,  thanks for your thorough explanation. 

[Cap]

On 4/16/2022 at 4:53 PM, Randyjaco said:

...The big surprise was my mileage went up by 4 MPG...

 

That is a big surprise.  I don't understand how your fuel economy would change that much by removing a flapper that is usually wide open.  But its good to hear that you are happy with the result.

 

Cap

[Hosstage]

5 minutes ago, Cap said:

 

That is a big surprise.  I don't understand how your fuel economy would change that much by removing a flapper that is usually wide open.  But its good to hear that you are happy with the result.

 

Cap

I have a feeling that the flapper was not wide open.

[alegerlotz]

1 hour ago, Cap said:

 

That is a big surprise.  I don't understand how your fuel economy would change that much by removing a flapper that is usually wide open.  But its good to hear that you are happy with the result.

 

Cap

I think that the conclusion here is that some of what the OP was complaining about with his bike was due to the flap not being wide open when it should have been.

 

Randyjaco (OP), have you noticed any difference in low end torque with the flap removed?

[Randyjaco]

I never experienced any low-end problems. The bike has always run as expected up to about @75 mph. Above that I always felt that the performance was lacking. After dealing with the valve itself, I feel that the valve was oscillating at high speed. I could move the valve using a finger or right angle tool. There is significant impulse and pressure in that area at high RPM. That could cause the valve to move back and forth depending on how well it was adjusted. Possibly mine was just loose at the factory. So I think it was severely affecting exhaust flow, thus causing a loss of power and require more fuel. I may be wrong, but that is my take. Meantime my bike is performing closer to my original expectations  

[Scott9999]

Well, gee, I'm glad I spotted this thread.  I had no idea that there were problems with the Exhaust flapper/valve.   Gotta update my "To Do" list.

 

"16)  R&R exhaust flapper valve; ensure it opens and closes properly or just remove. (PB blaster to clean, and then spray high temp copper anti-seize or graphite to lube)"

 

Y'all will notice that there are 15 other "high priority gotta do" items on that list.  🙄  I guess that I'm kinda backed up on my shop work.

 

I just LOVE my nearly-maintenance-free Beemer.  🤣🤣🤣  I wonder what it's like to actually ride the thing.

[Paul De]

You can hear if your flapper valve is working, or not.  Normally about a minute after ignition off you’ll hear the servo motor rotating it into either full open, or closed (not sure which). If it is hung up there probably is no sound if stuck, or a labored sound if sticking. I’ve wondered if I should get in there and apply a dab on the pivot points with some high temp pure nickel Never-Seez I have on the shelf as it is rated to not burn up to 2400F.  But not sure if any of the nickel flake happened to get down stream if it would poison the catalyst, so I have  not done it yet because my valve still of functioning well.

 

 

DR went into nice deep dive on reversion and all I’ll add is that it can increase power across the rev band if implemented to improve performance, but in the case of the Waterhead it is for noise control.  If it was for performance my guess is the volume of the header pipes ahead of the flapper would need to be a lot larger. Reversion also has application on the intake side of things as well.   Back in the 70’s and 80’s HD XR 750 flat track owners usually had several lengths of intake tracts that helped with throttle response and power delivery for a given track and final gearing.  But I digress.
 

Being the old fahrt that I am the Waterhead has plenty of go if the flapper is working properly and I appreciate the toned down exhaust note while cruising along and then having a distinct powerful bark when driving frisky and being WFO on the throttle. So if my flapper hangs up, I'll try to fix it.

[dirtrider]

2 hours ago, Paul De said:

You can hear if your flapper valve is working, or not.  Normally about a minute after ignition off you’ll hear the servo motor rotating it into either full open, or closed (not sure which). If it is hung up there probably is no sound if stuck, or a labored sound if sticking. I’ve wondered if I should get in there and apply a dab on the pivot points with some high temp pure nickel Never-Seez I have on the shelf as it is rated to not burn up to 2400F.  But not sure if any of the nickel flake happened to get down stream if it would poison the catalyst, so I have  not done it yet because my valve still of functioning well.

 

Afternoon Paul

 

The problem you are going to have is getting that high nickel grease into the actual shaft bearing area. I'm not sure how you will actually get it worked into the needed areas? Just smearing it on the exposed shaft areas won't work as that nickel grease won't migrate to where it needs to be. 

 

I have worked on a few that had lazy or sticking valves & have found that GM heat riser lube (remember heat riser valves?) works pretty good (that was made for lubricating the heat riser valve shafts in a very hot exhaust manifold environment). I'm just not sure where you can find heat riser lube anymore.  (I guess I need to start looking as I only have a couple of cans remaining on my shelf)

 

You are probably going to need something that is fairly heat resistant but with a thin enough carrier fluid to migrate into the bearing areas.  

 

 

 

 

[Skywagon]

37 minutes ago, dirtrider said:

remember heat riser valves?

 

I still have cuts on my knuckles.

 

Here is a thread on 2015 FS Repair.  Voice is British ( I think ) so not sure if bike is same as US...but will give you an idea.

 

 

[gary45]

I mix lots graphite powder in regular grease, have always used it on exhaust, grease burns off leaving graphite, always comes undone easily. On my 18 used a small screw driver and put a fair bit on the shaft where the return spring is, applied a bit on the base of the valve shaft inside the pipe, seems to have melted into bushing areas, the valve was sticking, has been working OK, plan on adding a bit again. I do not like the extra noise when it sticks open, I wish the RT was as quiet as the GTL I had.

 

www. beemershop.com - video explaining hoe BMW ESA works

[wbw6cos]

My flapper valve has a real pronounced squeak.   I have to apply some high temp grease (do not remember, off hand) and use these to place it in and around the shaft.   Just be sure to clean thoroughly when you finish; it is hard to floss with grease still on them.

 

[Paul De]

Like the soft picks idea,  also could probably thin the Never-Seez with mineral spirits to let it flow into the bearing area.  Just will have to let us sit overnight to allow flammable carrier to evaporate.   In the old days I might have used perchloroethylene which isn’t flammable, but is a known carcinogen…Other than that it is a good nonflammable solvent

[hound]

5 hours ago, dirtrider said:

 I'm just not sure where you can find heat riser lube anymore.  (I guess I need to start looking as I only have a couple of cans remaining on my shelf)

 

You are probably going to need something that is fairly heat resistant but with a thin enough carrier fluid to migrate into the bearing areas.  

 

 

 

 

 

I found This closest i could find. I give it a shot every now and then, so far so good

[wbw6cos]

What are the reasons for y'all trying to lube that flapper valve?   

 

Is the noise level of that flapper valve cycling increasing to the point of concern?

 

I thought mine was noisy, but.....

 

Thanks.

[gary45]

It seems to stick open, stop cycling, 

[dirtrider]

8 hours ago, wbw6cos said:

What are the reasons for y'all trying to lube that flapper valve?   

 

Is the noise level of that flapper valve cycling increasing to the point of concern?

 

I thought mine was noisy, but.....

 

Thanks.

Evening William

 

The noise does bother some riders but with the noise at least you know it's probably working OK.

 

The ones I have lubed were mainly due to the valve sticking or hanging up in operation (or just a worry that it might be sticking when in operation).  

 

I haven't worked on that many but the few I have worked on typically  started sticking after winter storage, or after a period of not riding, (most riders in my area stop riding throughout the winter months due to salt & ice on the roads).

 

I'm sure BMW probably ran a number of high mile durability tests on the valve equipped motorcycles but my guess is they didn't include much extended storage testing in their durability schedules.    

[LAF]

I did a write up on this flapper valve cleaning when I did my 15 RT.

 

Ehaust Valve Cleaning

 

You need a carbon remover as it hanging up is usually cased by exhaust build up around the diameter of the exhaust pipe and on the butterfly itself.  As I say in the link I read about this on some UK forums first.

 

I did find that a slur made from high temp copper grease and a high temp silicone spray and a artist paint brush and I used a nylon stick and just kept forcing it around the spindles.  I also used a cable lube on the cables.  I used picture wire to tie a rag onto and forced it f past the flapper and pulled it close to the flap when I sprayed any cleaner so I did not contaminate the cat. 

 

You can see the difference in the post and did it as maintenance task twice in 26K on the 15 RT.  

 

Not sure what else you can do but I do believe it is carbon on the exhaust pipe and butterfly hanging up the flapper.  From what I understand it is 1200 bucks for the header alone.  Of course that would be Akrapovic header range so that would never happen. 

 

And this is the first report I have seen where someone has knocked out the butterfly.  Good job for sure.

[Paul De]

The noise of the valve in operation hasn't bothered me and I only actually hear the flapper valve servo motor about a minute after shut down.  So far it sounds like it did since new, no squeaks, or a prolonged and labored sound, or worse no sound.  I sort of like the familiar auditory cue that it is operating normally after every power down. I guess coming from a '99RT having weird a whirring sound coming from the bike is now somehow comforting.  When underway I never hear the servo operating above the normal clatter of the running engine and the only clue it is working properly is how much more throaty the exhaust note gets under hard acceleration...and the fact that the motor pulls hard up into the upper RPMs of the power band.   So, I'm in the yeah it's a BMW and it will make noises that no other bike does camp...some of them are kinda weird too.

[Rainman48]

If you have a GS-911 diagnostic tool you can test the exhaust flapper to see if it's sticking or not in a very positive way with a pass/fail test you can see and hear.  Also eliminates any doubt what you're hearing as a warm bike cools down or waiting for the CANBUS to shut down.
I may save some of these ideas for lubing it if it happens to my '16 RT.  So far so good.

 

[wbw6cos]

The trick is trying to cycle it and put lube in the shaft area.  That thing is QUICK!  

[profbodryak]

Hi All, 

 

Has anyone tried this? 

 

https://www.revzilla.com/motorcycle/servo-buddy-bmw-2010-2017?sku_id=1185159

 

My dealer has diagnosed my check engine light mapping to a group that has the servo motor in it (only comes on after a ride once the engine is shut off). 

[Oldrider51]

I have a 2016 R1200RS with a full Akrapovic exhaust system that removed the flapper valve and drive motor and in the place of the drive motor I installed the servo-buddy and had no problems and no warnings on the instrument panel. So, it worked for me.

 

[profbodryak]

13 hours ago, Oldrider51 said:

I have a 2016 R1200RS with a full Akrapovic exhaust system that removed the flapper valve and drive motor and in the place of the drive motor I installed the servo-buddy and had no problems and no warnings on the instrument panel. So, it worked for me.

 

Where did you mount the servo buddy? I have a stock exhaust system and just wondering how it would work since I'd need to ensure that the flapper valve remains in the fully open position permanently. 

[profbodryak]

Got a clarification from the dealer. By default, the valve remains fully open when the ignition is fully turned off so can be installed then. 

[Oldrider51]

23 hours ago, profbodryak said:

Where did you mount the servo buddy? I have a stock exhaust system and just wondering how it would work since I'd need to ensure that the flapper valve remains in the fully open position permanently. 

After removing the stock servo motor and plugging in the servo buddy I used to ties to secure it behind the transmission with other wires already there. Just completed a 1900 mile trip and had no problems. If your bike is an RT I have seen the short pipe that replaces the one on the RT thar houses the flapper. At least I believe it was a wetted RT.

[Yuro]

On 4/18/2022 at 5:12 PM, Randyjaco said:

I never experienced any low-end problems. The bike has always run as expected up to about @75 mph. Above that I always felt that the performance was lacking. After dealing with the valve itself, I feel that the valve was oscillating at high speed. I could move the valve using a finger or right angle tool. There is significant impulse and pressure in that area at high RPM. That could cause the valve to move back and forth depending on how well it was adjusted. Possibly mine was just loose at the factory. So I think it was severely affecting exhaust flow, thus causing a loss of power and require more fuel. I may be wrong, but that is my take. Meantime my bike is performing closer to my original expectations  

I have a new 1250 GSA with flapper.   I rode it from Chicago to STL on my way to the Springfield rally and got...34mpg.     It had 3500 miles on it then.   Bike had one rider, my camping stuff on a pillion rack and alum cases with some stuff....not overloaded or even close.  No top case.  I had it down to poor aero of the alum cases and the use of a touring screen...and the wind was not blowing in my favor, but cruise control was set at 78mph for 90% of the tank, no hero moves or hooning for about the whole tank.    That's pathetic!    

 

I don't get any errors, but I'm going to have a look at this valve.   I don't feel like I'm getting good mpg with this bike generally and that something may be a little wrong.   It feels strong but also like  spark advance is right on the edge all the time, so it should be doing great on gas.  I kind of expected better mpg than the '17 RT due to shift-cam and all the other wizz-bang stuff on this machine.  

 

Premium is near $7 here in Chicago.