Exhaust flap

[Pukmeister]

With the link between cylinders, each high velocity exhaust pulse leaving the pipe helps to scavenge waste gasses from the other cylinder, which is why the link piece is not too far from the cylinders.

If it was a longer two-into-one pipe with the link further downstream it wouldn't work as the exhaust gas has lost too much energy to be effective.

 

[GlynnJ]

Being a euro 5 RnineT mine is a bit quiet so I’ve tried removing the cables as the consensus is that it’s just for noise reduction, but the bike doesn’t seem to have the same mid range shove without the flap connected, am I wrong in thinking this?

If you check out the YouTube link above you’ll see that the valve is purely for noise suppression at certain revs. TBH, I hate to think how loud it would be without! Not a quiet bike by any means.


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[Steptoe]

If it was a two stroke, which requires back pressure to help seal the open port during the exhaust cycle ,

I'd have said absolutely, spot on ....

But its a four stroke, so the exhaust port is closed once the exhaust gasses have exited the chamber ,

Any pressure going back toward the cylinder will meet a closed valve.

I'm no exhaust expert, and I've often wondered why they have the balance pipe between the two cylinders, why not remove and have a bmw burble ??

Ah just doing some googling - the backpressure is for scavenging apparently

With the link between cylinders, each high velocity exhaust pulse leaving the pipe helps to scavenge waste gasses from the other cylinder, which is why the link piece is not too far from the cylinders.

If it was a longer two-into-one pipe with the link further downstream it wouldn't work as the exhaust gas has lost too much energy to be effective.

Good luck trying to get a decent smooth tick over on a bnw without a balance pipe near the cylinders….

 

[botus]

Being a euro 5 RnineT mine is a bit quiet so I’ve tried removing the cables as the consensus is that it’s just for noise reduction, but the bike doesn’t seem to have the same mid range shove without the flap connected, am I wrong in thinking this?

valve overlap (both inlet and exhaust open at the same time) increases the more manufacturers take higher performance bikes up the rev range - without VVT (variable valve timing) torque mid range disappears - the Twin Cam's rev 750 rpm more and have a bit more of a top end hit (where you never needed it) - an exhaust flap valve can influence the amount inlet gases escape at lower revs (helping keep it where you want it) - thus its use can increase mid range grunt, and substantially reduce emissions - and you can also get a win shutting up the stupid noise

done 35k miles ripping to death my older Hex GS bike - no one ever bothered to notice - but now in exactly the same parts of the world - I now see the ambulances rushing to all these pedestrians getting whiplash injuries when suddenly looking around, if I so much as open the throttle a smidge on the Twin Cam (with is 100% standard exhaust)

on the 1250GS with its shift cam you can easily feel the bike swapping cam position - finding the power has noticeable bumps in its curve that come and go based on throttle postion and revs - the 1300GS has now got things right - and its power curve is way more usable - with a far cleaner curve making it a much better bike to thrash to death (and way safer), as you can feed in the power on the throttle reliably - not have the 1250s electronics interfering as a lumpy curve messes with rear grip

 

[Slipperyeel]

My method is going to be ,

Syringe of Special lube Nickel /graphite past

squirt onto butterfly spindle at lower & upper point then move spindle back and forth, until the blob of lube has seeped into the gap in the shaft ( or as close as)

if i can get the end cap off, ill attack the bearing from that side

I also thought about removing that cap, but it then occurred to me it has to be gas tight...which I didn't anticipate being able to achieve after removal! But get some pictures of you do go for that option. I'm still intrigued if there's graphite bushes or some other possibility!


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[Santa-2512]

I also thought about removing that cap, but it then occurred to me it has to be gas tight...which I didn't anticipate being able to achieve after removal! But get some pictures of you do go for that option. I'm still intrigued if there's graphite bushes or some other possibility!


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i seem to recall some one had managed to get that cap off , or i may have been dreaming

either way next week

 

[Santa-2512]

Good luck trying to get a decent smooth tick over on a bnw without a balance pipe near the cylinders….

Burble over tick over hmm, I thought it was meant to be WOT all the way mista

 

[Pukmeister]

on the 1250GS with its shift cam you can easily feel the bike swapping cam position - finding the power has noticeable bumps in its curve that come and go based on throttle postion and revs - the 1300GS has now got things right - and its power curve is way more usable - with a far cleaner curve making it a much better bike to thrash to death (and way safer), as you can feed in the power on the throttle reliably - not have the 1250s electronics interfering as a lumpy curve messes with rear grip

I’m sure you mean well, but you don’t half spout some bollocks.

My 1250 GSA is seamless, no matter how I ride it I cannot tell when the shift cam operates. Its fuelling is silky smooth and sublime to ride, easily the best GS I’ve owned.

I rode the 1300 demo as a loan bike during a dealer service, the engine was fine but much harsher than my 1250 (possibly due to a lot less mikes on it) and I much prefer my 1250 given the choice.

 

[autogs]

valve overlap (both inlet and exhaust open at the same time) increases the more manufacturers take higher performance bikes up the rev range - without VVT (variable valve timing) torque mid range disappears - the Twin Cam's rev 750 rpm more and have a bit more of a top end hit (where you never needed it) - an exhaust flap valve can influence the amount inlet gases escape at lower revs (helping keep it where you want it) - thus its use can increase mid range grunt, and substantially reduce emissions - and you can also get a win shutting up the stupid noise

done 35k miles ripping to death my older Hex GS bike - no one ever bothered to notice - but now in exactly the same parts of the world - I now see the ambulances rushing to all these pedestrians getting whiplash injuries when suddenly looking around, if I so much as open the throttle a smidge on the Twin Cam (with is 100% standard exhaust)

on the 1250GS with its shift cam you can easily feel the bike swapping cam position - finding the power has noticeable bumps in its curve that come and go based on throttle postion and revs - the 1300GS has now got things right - and its power curve is way more usable - with a far cleaner curve making it a much better bike to thrash to death (and way safer), as you can feed in the power on the throttle reliably - not have the 1250s electronics interfering as a lumpy curve messes with rear grip

Again what a load of crap! The shift cam is seamless in operation

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[botus]

I’m sure you mean well, but you don’t half spout some bollocks.

you can claim what you want.... the 1250 has a lumpy bumpy curve that's horrible - NOTE: the issue with just staring at most dyno torque curves (that do show the 1250 as very spiky, and also show up a bit on the 1300) - you seldom ride fast bikes with the throttle on its end stop

the 1300 makes enough power you aren't holding it on full chat all the time like you do on the 1250. With the far lower output of the 1250, you often ride it flat out meaning the peaky spikes in the torque curve below force the tyre to let go, which means the electronic nanny is muddling itself up trying to help

where as you'll see on the 1300 the massive extra grunt at 3500 rpm helps you find and get used to the far smoother curves at speeds many can cope with - as they learn to ride on the 1300 the rider gets to manipulate the throttle to optimise rear grip and the electronics don't interfere with you getting on with it (when in dynamic pro)

sadly this doesn't have the other two air cooled ones - its just the LCs

 

[Pukmeister]

My 1250 goes like fuck and my patented arse-o-matic dyno says its plenty good enough for me.

I don't look at graphs when I'm riding, I'm too busy having fun.

I can't recall ever riding my 1250 flat out, I'm not on track and value keeping my license after the last Police chat and fine/points I received when out riding my R1.

Nor have I ever felt the electronics intervene, despite always riding it in Dynamic Pro with moderate anti-wheelie enabled.

As for the extra grunt of the 1300, whatever the graphs say I found it boring and anodyne in its delivery although that may have been down to it being a brand new zero-miles demonstrator.

 

[botus]

Again what a load of crap! The shift cam is seamless in operation

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see the HIDEOUS dotted RED spikes at 5000 and 6400 rpm above

yes - if you don't know what full throttle is, you likely never found them

 

[botus]

As for the extra grunt of the 1300, whatever the graphs say I found it boring and anodyne in its delivery although that may have been down to it being a brand new zero-miles demonstrator.

if it was a demo bike it might still have had the running in moped mode activated - the one they gave me had that on - but magically it got turned off to full on nutter machine

I also found a second bug just like my 1290, if you rip it to death hard enough in certain circumstances there are occurrences the anitwheelie forgets how to work and suddenly it stands on it back wheel - which comes as quite a surprise when you spent all day with it stopping it getting more than a few inches of lift

nannies are a nuisance

 

[Santa-2512]

So,
Ultrasonic bath, cleaner & Nickel antisieze paste ordered

When i get some free time over the next week, i'll cut the old flap off and start the process

 

[Steptoe]

A three pager about an exhaust flap .. and it’s still rambling on ..

who’d have thought.

 

[zoltan]

A three pager about an exhaust flap .. and it’s still rambling on ..

who’d have thought.

Discuss

 

[Santa-2512]

So all parts have arrived

The flap has again slowed/ limited travel

I've run a degass cycle on the ultrasonic cleaner,

The flap is in @ 40c for 30 mins, bake until golden brown

I'm going to do a cleaning cycle
Recheck it and repeat,

Once (if) I can get it back to a full cycle,

I'll lube it and see if I can warm it with a

blowlamp to get the lubricant to flow

( I suspect I won't) given the high temps of the lubricant.

If all fails I'll grab a new one

 

[Steptoe]

I’ve left a few in a bowl of diesel fuel for a few days and it’s freed them up.

 

[Pukmeister]

I’ve left a few in a bowl of diesel fuel for a few days and it’s freed them up.

We had to do the same on Deltic (2-stroke) diesel exhaust flaps on minesweepers. A filthy horrible job.

Thank fuck they are now running Caterpillar engines !

Also used commercial grade oven cleaner gel to dissolve carbon deposits, but not sure what that would do to a BMW exhaust valve if left on overnight.

 

[Santa-2512]

Well the first cycle was partially successful, but not 100% so I soaked it in wd 40 ,as I couldn't find any plusgsas, il. Rinse and repeat tomorrow