Exhaust valve, poor cold starting 1200

[Engineer]

Exhaust valve is a very specific part; you’d have thought an engineer might have known the difference

just realised what you were getting at I thought it was clear from the context which 'valve' I was referring to as I can't imagine the engine ever starting with the exhaust poppet valve being stuck open as there would be no compression

 

[casbar]

I’m not sure this is the case - it goes through a cycle when you turn the ignition, but,I think, returns to fully open at start. Hence the rather “explosive” startup sound.

I’m still saying (despite the explanations) that the flappy valve is u related to your starting and I’d ask when the plugs were last changed.


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It does, it does not stay closed on startup. It cycles and then goes back to fully open. We have one 1200RT where the flap has been stuck open for years, no issues ever with starting. I freed it off, but it is starting to stick again. I had a 1200LC RT that I rode around for nearly a year with the flap stuck open, didn't notice anything. In the end the headers got replaced under warranty. Flap does nothing to aid startup. The flap is for noise emissions only. I would have thought Knutk would know that as he is normally quite knowledgeable. This was also confirmed by the BMW techs who told me that if I couldn't get it replaced under warranty to bosh the thing out, as it wouldn't make a blind bit of difference. Some replace the servo with an emulator to fool the ECU into thinking the flap is there so no error codes. So does that create back pressure then?

 

[spoonz]

It does, it does not stay closed on startup. It cycles and then goes back to fully open. We have one 1200RT where the flap has been stuck open for years, no issues ever with starting. I freed it off, but it is starting to stick again. I had a 1200LC RT that I rode around for nearly a year with the flap stuck open, didn't notice anything. In the end the headers got replaced under warranty. Flap does nothing to aid startup. The flap is for noise emissions only. I would have thought Knutk would know that as he is normally quite knowledgeable. This was also confirmed by the BMW techs who told me that if I couldn't get it replaced under warranty to bosh the thing out, as it wouldn't make a blind bit of difference. Some replace the servo with an emulator to fool the ECU into thinking the flap is there so no error codes. So does that create back pressure then?

I’ve never studied what the flap does and when ( does it close after xxx seconds of run or if you blip the throttle etc ) and if it has changed on later bikes with stiffer emission regs. But what knut said about re burn is 100% valid though and I’m pretty sure Bmw will be doing it. All exhaust systems will generate a reverse pressure wave (back pressure) with or without a flap and manufacturers use valve overlap to allow that pressure to re ingest a % of the exhaust gasses back into the cylinder. The tighter the regs the more they probably use the technology as it means they can maintain cat size and not have to lean off the bike to still get decent emissions.

The Aprilia v4 series of bikes uses a similar valve in the exhaust and it’s documented in their training info as an aid to noise reduction, cat heating, and emissions reduction. I don’t have access to any BMW info but I wouldn’t be the least bit surprised if the valve has evolved in use from a simple noise reduction device in early incarnations to something similar on euro 4/5 bikes. I doubt it makes diddly squat difference to the general running of the bike though.

 

[casbar]

I’ve never studied what the flap does and when ( does it close after xxx seconds of run or if you blip the throttle etc ) and if it has changed on later bikes with stiffer emission regs. But what knut said about re burn is 100% valid though and I’m pretty sure Bmw will be doing it. All exhaust systems will generate a reverse pressure wave (back pressure) with or without a flap and manufacturers use valve overlap to allow that pressure to re ingest a % of the exhaust gasses back into the cylinder. The tighter the regs the more they probably use the technology as it means they can maintain cat size and not have to lean off the bike to still get decent emissions.

The Aprilia v4 series of bikes uses a similar valve in the exhaust and it’s documented in their training info as an aid to noise reduction, cat heating, and emissions reduction. I don’t have access to any BMW info but I wouldn’t be the least bit surprised if the valve has evolved in use from a simple noise reduction device in early incarnations to something similar on euro 4/5 bikes. I doubt it makes diddly squat difference to the general running of the bike though.

You maybe correct in that the flap has evolved. On the early bikes with it, if it stuck open there was no visible indication for the rider. But there was a fault code on the ECU. On the newer models and my current 1250, if the flap sticks, it throws and engine warning light. But I still believe it does nothing to help with starting and certainly on my 2014 bike and a 2015 bike I have in the garage currently, the flap not working doesn't impact anything but noise. There are pages and pages on discussion about this flap. Once it starts squeaking you are doomed, greasing it inside the exhaust with high temp grease according to loads of others, does nothing but a short term fix. I used to grease the mechanism and put grease on mine, but it still ended up being replaced twice. On my 1250 I'm not bothered yet, as I still have over a years warranty left and I'll have probably changed the bike again before I need to worry about it

 

[malcopopolo]

When I read this thread, it strikes me that perhaps some of the gentlemen in her posting perhaps should do their homework and read up before posting condescending ass-hole comments.

What used to work on older bikes is not necessarily valid for new ones.

The thing is: @Engineers post is indeed relevant.

The strict requirements for the Euro-4 and and Euro-5 means new ways of controlling the engine compared to older bikes.

A cold engine requires a richer fueling than a warm engine.
While this used to be simply a matter of richening up the fueling, the newer emission regs. interfers at all stages of running an engine to a much higher degree than for pre Euro-4 engines.

By closing the exhaust flap, a backpressure will be built in the exhaust flow. This means that when the exhaust valves opens and the pistions try to empty the cylinder for burned gasses, the backpressure caused by the exhaust flap will reduce the flow, and some of the unburnt gasoline (a result from the less efficiency of a cold engine) will be kept in there and be burned on the next stroke. This again allows for the ECU to add slightly less extra fuel to the cold engine and thereby less pollution.

If the flap does not close, this will result in a too lean mixture for the engine when cold, and this corsponds to the symptoms @Engineer described.

Who is providing ass-hole comments now? The flap is purely to reduce noise.

 

[knutk]

It does, it does not stay closed on startup. It cycles and then goes back to fully open. We have one 1200RT where the flap has been stuck open for years, no issues ever with starting. I freed it off, but it is starting to stick again. I had a 1200LC RT that I rode around for nearly a year with the flap stuck open, didn't notice anything. In the end the headers got replaced under warranty. Flap does nothing to aid startup. The flap is for noise emissions only. I would have thought Knutk would know that as he is normally quite knowledgeable. This was also confirmed by the BMW techs who told me that if I couldn't get it replaced under warranty to bosh the thing out, as it wouldn't make a blind bit of difference. Some replace the servo with an emulator to fool the ECU into thinking the flap is there so no error codes. So does that create back pressure then?

Over the last few years, the use of the exhaust flap has evolved. So when asking for information about it's function, the answer will depend on whether the bike is pre -16 (Euro-3), 16 - 20 (Euro 4) or >-20 (Euro -5).
In addition to the CO emission, the focus has also been increased on the NOx part. And the challenge is that while a hot burning combustion is good for reduction of the CO (converted to CO2 in the cat), the same heat is terrible for avoiding the NOx part.

In order to reduce the temperature in the combustion chamber, one trick, the EGR valve used by cars, is to route some of the exhaust back to the cylinder, where the already burned or partly burned exhaust will fill up a bit of the space, thereby allowing for less fresh air and fuel mix. This will of course reduce the maximum output of the engine, but emission control focus mainly on conditions at less than full power. Cars do also have exhaust flap. But serving as noise reduction it is placed way back on the car. This distance from the cylinders means the flap has less effect on anything but noise reduction, but cars have the EGR valve.

In bikes, where the flap is fairly close to the cylinder, closing the exhaust flap and reducing the flow and speed of the exhaust will serve several functions. Noise is still a major part. But the flap also stops / (and even may push back) some of the exhaust (Think of the exhaust as chunk of gases that are pushed in a short burst out of the cylinder. When the ball of gases hit the flap (after passing the cat) it will bounce back. A lot of it will stop in the cat, but some of it will reach all the way and go back in. This will also help for a quicker warmup of the cat. But all of this action must be balanced, as the extra heat is good for the cat and bad for the NOx, where-as filling the cylinder with exhaust will require less fuel and air, cooling the combustion chamber, which is good for the NOx and bad for the CO and CO2 )

For the manufacturer, this is a delicate balance, where they strive to obtain several different goals that contradicts each other (cold and warm at the same time).
Thus, messing with any one of the parts in this chain of events may screw up the entire process.

Also, searching the net for information about how it works may be a pain. BMW uses the same controllers and software for their cars and bikes (hence, ISDA, a car system, also handles the bikes). When you search and find technical information, it does explain a lot of the chemical reactions, timing and formulas etc, but fail to mention if it's being used in cars, bikes or both. Most of the time, the descriptions covers both. But cars are a few years ahead of the bikes when it comes to implementations, thus even if I understand the descriptions and refer to them, I can not completely rule out that it has not yet been implemented to the bikes, even now with Euro-5 (cars are Euro 6).

This bugs the sh...t out of me, and I guess I have to walk the steps to my garage and pull of the mufler on my 1250 to verify my explanations. And if I fall flat on my face, well, being a married man I feel confident that I am capable of handling the verbal abuse that comes along

 

[Engineer]

Over the last few years, the use of the exhaust flap has evolved. So when asking for information about it's function, the answer will depend on whether the bike is pre -16 (Euro-3), 16 - 20 (Euro 4) or >-20 (Euro -5).
In addition to the CO emission, the focus has also been increased on the NOx part. And the challenge is that while a hot burning combustion is good for reduction of the CO (converted to CO2 in the cat), the same heat is terrible for avoiding the NOx part.

In order to reduce the temperature in the combustion chamber, one trick, the EGR valve used by cars, is to route some of the exhaust back to the cylinder, where the already burned or partly burned exhaust will fill up a bit of the space, thereby allowing for less fresh air and fuel mix. This will of course reduce the maximum output of the engine, but emission control focus mainly on conditions at less than full power. Cars do also have exhaust flap. But serving as noise reduction it is placed way back on the car. This distance from the cylinders means the flap has less effect on anything but noise reduction, but cars have the EGR valve.

In bikes, where the flap is fairly close to the cylinder, closing the exhaust flap and reducing the flow and speed of the exhaust will serve several functions. Noise is still a major part. But the flap also stops / (and even may push back) some of the exhaust (Think of the exhaust as chunk of gases that are pushed in a short burst out of the cylinder. When the ball of gases hit the flap (after passing the cat) it will bounce back. A lot of it will stop in the cat, but some of it will reach all the way and go back in. This will also help for a quicker warmup of the cat. But all of this action must be balanced, as the extra heat is good for the cat and bad for the NOx, where-as filling the cylinder with exhaust will require less fuel and air, cooling the combustion chamber, which is good for the NOx and bad for the CO and CO2 )

For the manufacturer, this is a delicate balance, where they strive to obtain several different goals that contradicts each other (cold and warm at the same time).
Thus, messing with any one of the parts in this chain of events may screw up the entire process.

Also, searching the net for information about how it works may be a pain. BMW uses the same controllers and software for their cars and bikes (hence, ISDA, a car system, also handles the bikes). When you search and find technical information, it does explain a lot of the chemical reactions, timing and formulas etc, but fail to mention if it's being used in cars, bikes or both. Most of the time, the descriptions covers both. But cars are a few years ahead of the bikes when it comes to implementations, thus even if I understand the descriptions and refer to them, I can not completely rule out that it has not yet been implemented to the bikes, even now with Euro-5 (cars are Euro 6).

This bugs the sh...t out of me, and I guess I have to walk the steps to my garage and pull of the mufler on my 1250 to verify my explanations. And if I fall flat on my face, well, being a married man I feel confident that I am capable of handling the verbal abuse that comes along

I'd like to know what you discover, it will save me pulling the silencer off again, I was pretty sure it remained closed after I turned on the ignition and waited a while - what happens when you hit the starter I don't know because I didn't want to run the bike with no silencer attached.

P.S. looking at the flap/valve I would have thought when closed it would provide quite a severe restriction of the gas flow, to the point where it must have far more effect upon the engine than simply noise.

 

[malcopopolo]

I'd like to know what you discover, it will save me pulling the silencer off again, I was pretty sure it remained closed after I turned on the ignition and waited a while - what happens when you hit the starter I don't know because I didn't want to run the bike with no silencer attached.

P.S. looking at the flap/valve I would have thought when closed it would provide quite a severe restriction of the gas flow, to the point where it must have far more effect upon the engine than simply noise.

As soon as you rev the bike the flap opens...

 

[casbar]

I haven't looked at the flap on my 1250, so my experience has been with 2014 and 2015 bikes. So the theory that the use of the flap has evolved since EU4 and 5 is quite probable. It would also explain why the stuck flap now throws an engine warning light as opposed to just a code on the EUC. So it will be good to understand what now actually happens. Like Engineer, don't think I would start the bike without the silencer on, my neighbours would not be impressed

 

[spoonz]

You could observe the servo re determining what it’s doing and when if you make a note of it’s pulley orientation open/closed pre startup.

It might not be a case of open and closed either, it could be anything in between under different situations. ( eg a dynamic mode, compared to a road mode) as well rpm etc.

 

[casbar]

You could observe the servo re determining what it’s doing and when if you make a note of it’s pulley orientation open/closed pre startup.

It might not be a case of open and closed either, it could be anything in between under different situations. ( eg a dynamic mode, compared to a road mode) as well rpm etc.

Actually it is quite easy to whip off the black cover over the top of the flap where the cables join to observe what is happening. Might have a look at the weekend if nobody else has come up with what is happening

 

[Engineer]

Actually it is quite easy to whip off the black cover over the top of the flap where the cables join to observe what is happening. Might have a look at the weekend if nobody else has come up with what is happening

Just a note - anticlockwise rotation is open, this is the position with the ignition off and the position the spring would hold it in if the cables broke.

 

[Daffy]

Over the last few years, the use of the exhaust flap has evolved. So when asking for information about it's function, the answer will depend on whether the bike is pre -16 (Euro-3), 16 - 20 (Euro 4) or >-20 (Euro -5).
In addition to the CO emission, the focus has also been increased on the NOx part. And the challenge is that while a hot burning combustion is good for reduction of the CO (converted to CO2 in the cat), the same heat is terrible for avoiding the NOx part.

In order to reduce the temperature in the combustion chamber, one trick, the EGR valve used by cars, is to route some of the exhaust back to the cylinder, where the already burned or partly burned exhaust will fill up a bit of the space, thereby allowing for less fresh air and fuel mix. This will of course reduce the maximum output of the engine, but emission control focus mainly on conditions at less than full power. Cars do also have exhaust flap. But serving as noise reduction it is placed way back on the car. This distance from the cylinders means the flap has less effect on anything but noise reduction, but cars have the EGR valve.

In bikes, where the flap is fairly close to the cylinder, closing the exhaust flap and reducing the flow and speed of the exhaust will serve several functions. Noise is still a major part. But the flap also stops / (and even may push back) some of the exhaust (Think of the exhaust as chunk of gases that are pushed in a short burst out of the cylinder. When the ball of gases hit the flap (after passing the cat) it will bounce back. A lot of it will stop in the cat, but some of it will reach all the way and go back in. This will also help for a quicker warmup of the cat. But all of this action must be balanced, as the extra heat is good for the cat and bad for the NOx, where-as filling the cylinder with exhaust will require less fuel and air, cooling the combustion chamber, which is good for the NOx and bad for the CO and CO2 )

For the manufacturer, this is a delicate balance, where they strive to obtain several different goals that contradicts each other (cold and warm at the same time).
Thus, messing with any one of the parts in this chain of events may screw up the entire process.

Also, searching the net for information about how it works may be a pain. BMW uses the same controllers and software for their cars and bikes (hence, ISDA, a car system, also handles the bikes). When you search and find technical information, it does explain a lot of the chemical reactions, timing and formulas etc, but fail to mention if it's being used in cars, bikes or both. Most of the time, the descriptions covers both. But cars are a few years ahead of the bikes when it comes to implementations, thus even if I understand the descriptions and refer to them, I can not completely rule out that it has not yet been implemented to the bikes, even now with Euro-5 (cars are Euro 6).

This bugs the sh...t out of me, and I guess I have to walk the steps to my garage and pull of the mufler on my 1250 to verify my explanations. And if I fall flat on my face, well, being a married man I feel confident that I am capable of handling the verbal abuse that comes along

Still haven’t thought it through properly, the flap is not a primitive form of EGR, its too far away from the cylinder and has a great big filter between and another cylinder also firing - the pulse wont bounce back. The purpose of the flap is a noise reduction measure that can coincidentally be used to heat the cat.

The flap on cars are 2 different things either a noise function as per RS5 Audi or an EGR flap as per lots of vehicles, they are not the same thing.

I’m not aware of a cold engine that meets emission standards except perhaps a Tesla, the holy grail with IC engines is to get them to operating temp in the least possible time.

 

[casbar]

Just a note - anticlockwise rotation is open, this is the position with the ignition off and the position the spring would hold it in if the cables broke.

That is correct. I have a video on my phone from one i freed on a 2015 RT. I know it closes and opens when the ignition is switched on. But not sure what it does on startup and idle.

 

[knutk]

Still haven’t thought it through properly, the flap is not a primitive form of EGR, its too far away from the cylinder and has a great big filter between and another cylinder also firing - the pulse wont bounce back. The purpose of the flap is a noise reduction measure that can coincidentally be used to heat the cat.

The flap on cars are 2 different things either a noise function as per RS5 Audi or an EGR flap as per lots of vehicles, they are not the same thing.

I’m not aware of a cold engine that meets emission standards except perhaps a Tesla, the holy grail with IC engines is to get them to operating temp in the least possible time.

In cars the flaps is at the rear, and serves a noise only function. And the EGR takes care of the emission part.
The theory I'm referring to is from a Bosch description, but they do not specify bike or car (basically the same computers, but adapted to vehicle), and as such I can not guarantee that BMW has implemented all of it. Neither do they specify the required distance between the flapper valve and the cylinder.

The cold engine will not be as clean as a warm engine, and the same goes for wide open throttle. The measurements for the emission control are taken when the engine is warm.
The Bosch description did not mention the meeting of any specific values for the cold start, just that it is an improvement (compared to not doing it), and the same for the improved warming of the cat, as well as the chilling effect of the remaining exhaust in the cylinder. This of course mean that it may be effective, or it may be next to nothing and mentioned only to please the bureaucrats. Meaning OP's description may indeed be correlated to the flap, but we can not rule out that it is a coincidence either.

But one thing is the Bosch descriptions for the capacity of their ECU, another thing is what BMW has implemented in our bikes, which probably is no more than what they can get away with. The emission demands for cars are even more strict than for the bikes, hence the many 'tricks' built into the ECU.

I'll have a look at my 1250 and see how it acts. In addition to the flapper valve position, I'll try to see if there are readings offered by GS911 that may shed a light on the fueling that reacts to the flapper valve. The valve is placed at a short distance from the cylinder, but there is a cat in-between.

I'll bring an update....

 

[spoonz]

Still havenÂ’t thought it through properly, the flap is not a primitive form of EGR, its too far away from the cylinder and has a great big filter between and another cylinder also firing - the pulse wont bounce back. .

Forgetting the purpose of the valve for a minute, ref a couple of your points.

If the cat ( I presume that’s what you mean by filter ) is a barrier to upstream pressure waves then it would equally be a barrier to the downstream pressure waves as well. That would be pretty bad for the efficiency of the exhaust. It will absorb some going both ways just because it’s a dense material but it’s not unidirectional and by design as unrestrictive as possible.

You imply cylinder 2 firing, blocks any upstream pressure waves reaching cylinder 1 during overlap. When cylinder 2 is firing its exhaust valve is closed so there is no exhaust pulse. The exhaust is in a low pressure state which is really the point of overlap. To use the low pressure in the exhaust relative to the intake charge to pull fuel/air into the cylinder and flush out the old. For cylinder 2 to have an exhaust pulse that influenced overlap on cylinder 1, both cylinders would need to have some degree of open exhaust valves at the same time.

I did some digging last night on the boxer just to see if I could move the debate forward on the servo valve and it’s use especially re euro 5. Beyond it obviously being for noise regs at least in part it’s hard to find anything other than forum chatter. There was a US magazine that claimed dyno testing showed a HP drop of 4/5 bhp on the 1250 if it was always open and surmised it must be being used for some volume matching at specific rpm. I also found from BMW that euro 5 gave them a headache re overlap on the boxer. The e5 regs were much tighter on unburnt fuel being drawn into the exhaust during overlap at idle and low rpm ( as knut was eluding to in his first post ). So they used shiftcam to knock back the overlap at the test points and increase it outside of them. On the r1800 boxer they had to drop overlap altogether to meet e5 and switch to 4 valves per cylinder instead.

So nothing really re the servo valve but clearly e5 moved the goal posts and maybe raises the potential that the valve use may have evolved too. Be interesting to see what the valve is doing and when in all modes.

 

[Engineer]

All I can add us that since I unstuck the exhaust flap/valve thingy, allowing it to close, the cold start engine stall issue has gone away. No other changes have been made and the change was immediate.

 

[casbar]

I just had mine apart on my 1250 to give it a lube. I can confirm on switch on, the flap moves from open to closed and back to open. On starting, the flap is open, but on tickover (once started) it moves to about half closed and stays there. Interesting thing was, when I switched off, the flap stayed half closed and didn't return to open until I switched the ignition back on and then it cycled from open to closed and back to open again. No engine warning lights, so assume my flap is working correctly, thought I was surprised on switch off, it didn't return to fully open on its own (wonder if it is starting to stick). On the 2015 I checked, the valve is only moving about 20mm so is basically stuck open, no starting issues or slow running issues, but that is a EU3 engine.

 

[Daffy]

Forgetting the purpose of the valve for a minute, ref a couple of your points.

If the cat ( I presume that’s what you mean by filter ) is a barrier to upstream pressure waves then it would equally be a barrier to the downstream pressure waves as well. That would be pretty bad for the efficiency of the exhaust. It will absorb some going both ways just because it’s a dense material but it’s not unidirectional and by design as unrestrictive as possible.

You imply cylinder 2 firing, blocks any upstream pressure waves reaching cylinder 1 during overlap. When cylinder 2 is firing its exhaust valve is closed so there is no exhaust pulse. The exhaust is in a low pressure state which is really the point of overlap. To use the low pressure in the exhaust relative to the intake charge to pull fuel/air into the cylinder and flush out the old. For cylinder 2 to have an exhaust pulse that influenced overlap on cylinder 1, both cylinders would need to have some degree of open exhaust valves at the same time.

I did some digging last night on the boxer just to see if I could move the debate forward on the servo valve and it’s use especially re euro 5. Beyond it obviously being for noise regs at least in part it’s hard to find anything other than forum chatter. There was a US magazine that claimed dyno testing showed a HP drop of 4/5 bhp on the 1250 if it was always open and surmised it must be being used for some volume matching at specific rpm. I also found from BMW that euro 5 gave them a headache re overlap on the boxer. The e5 regs were much tighter on unburnt fuel being drawn into the exhaust during overlap at idle and low rpm ( as knut was eluding to in his first post ). So they used shiftcam to knock back the overlap at the test points and increase it outside of them. On the r1800 boxer they had to drop overlap altogether to meet e5 and switch to 4 valves per cylinder instead.

So nothing really re the servo valve but clearly e5 moved the goal posts and maybe raises the potential that the valve use may have evolved too. Be interesting to see what the valve is doing and when in all modes.

I think you are reading too much on the internet and taking it as fact.

Yes the cat is a filter of a sort, it does form a restriction hence the reason why the exhaust is often discoloured in the area of the cat and why peeps often say that removing it lets the engine Rev freely.

2 cylinders doesn’t block pulses but smooths them out.

As to the exhaust running at a lower pressure to the inlet, again your applying car technology which isn’t present on a naturally aspirated GS.

 

[spoonz]

I think you are reading too much on the internet and taking it as fact.

Yes the cat is a filter of a sort, it does form a restriction hence the reason why the exhaust is often discoloured in the area of the cat and why peeps often say that removing it lets the engine Rev freely.

2 cylinders doesn’t block pulses but smooths them out.

As to the exhaust running at a lower pressure to the inlet, again your applying car technology which isn’t present on a naturally aspirated GS.

A cat obviously offers a restriction to flow but the least possible by design. Your suggestion it’s restrictive enough to prevent any reverse pulses though doesn’t hold water. If it allows flow out it can allow flow in. The colour of the cat area has naff all to do with restriction it’s entirely due to the operating temp of the cat. It’s combusting unburnt fuel in the exhaust stream so gets very hot.

The modern boxer motor uses overlap ( except the r1800 as I found out). Don’t take my word for it look it up. If the pressure in the exhaust was higher than the intake charge entering the cylinder during overlap then it would draw exhaust gasses back into the cylinder. BMW even reference the E5 1250 changing overlap because too much unburnt fuel was being drawn out into the exhaust. It has nothing to do with bike or car technology. Overlap is used on bikes, cars, petrol and diesel. It’s just an engine technology not a vehicle specific technology.