I am trying to definitely resolve the knocking during startup. In reading Clymer manual (pg 231) on the output shaft, the author refers to BMW Service Information Bulletin October 1988, No. 11 037 88 (2289). On the off chance my issue is a known deficiency and repairable at BMW’s cost, I am looking for information on the SIB and determine if anyone has discussed this with their BMW dealer.

Link:

http://dws.x10host.com/11tech/BMW_TSB.11_037_88_(2289)_K100_Output_Shaft_Gear_Lash_.pdf

Thanks!

Reading through the BMW Service Information Bulletin (1988) dealing with K100 Lash Gear Noise, I see BMW used different part descriptions from those found on the parts fiche. To this end, can you help translate the following part descriptions found in the service bulletin to BMW part numbers:

Part numbers are for 1987 K100

Rear output bearing
Output bearing retaining circlip 
Tension gear
Diaphragm spring
Annular spring
Gear carrier
Output gear

Thanks

Does anyone know if there was a similar service bulletin for the same noise on the K75?  The problem there was a very sloppy fit between the the balance shaft and the drive dog that spins it.

davemadsen wrote:On the off chance my issue is a known deficiency and repairable at BMW’s cost . . .

Repairable at BMW's cost on your 1987 K100RT Brick with >180,000 miles on it?  They'll likely be eager to allay your disappointment.

What year engine does the fiche refer to, if it's 85 and later, the service bulletin I think is 85 and earlier. They have some different parts. That could be the reason for the differences. If you can give a drawing or the other terms that might help. 

Because yours is 87 I think you don't have the tension gear diaphragm spring, or the output bearing retaining circlip.

Is the sound reduced or goes away when the engine gets warm?

If the sound disappears after removing the alternator, you might not need any of the parts you listed, even better, you might be able to fix it without going into the engine.

The referenced service bulletin may be for an earlier K100. The date of the bulletin is 1988 (revised in 1989) and states it is an amendment to an earlier 1986 bulletin.

The fiche is for a 1984-1988.

The knocking noise is only at idle and only before the engine gets to operating temperature. Once the bike is warmed up or under way, the knocking goes away. From reading on the forum it seemed the noise was a classic worn spring clip that sits on the output shaft, but if the noise can be resolved without tearing the engine apart, all the better.

If the spring clip refers to the annular spring, that was more of a problem with the earlier model, the spring was too strong. I guess that noise would remain if the engine was warm.

My first guess would be the rubber dampers in the absorber housing. They can get too hard with age and so have a reduced ability to absorb pulses. When the engine gets warm the rubber gets warmer and softens.

Hopefully I'm wrong. I think it's a non urgent problem. You might find pieces of rubber in the oil, or at the bottom of the sump. They're much heavier than water, so won't float.

You comments are food for thought. I agree this is a non-urgent issue but I have a bit of time so I thought I would tackle the knocking. From the fiche it seems like the dampers will take the same effort. Since it is non-urgent, I may elect to just turn the radio louder.

That would be what I might do, but I'm known for sometimes taking the easy way out. Maybe try removing the alternator, that's an easy thing to try, and there are rubber dampers there too. 

Now here comes a bunch of wild speculation, keep in mind it's only speculation, no big deal. 

Yes, if the tabs on the K75 output shaft are banging in their slots, that would cause a noise, but I think the increased clutch nut torque specified for the K75 over the K100, is to eliminate this as a possibility. I think of them as tabs more so than drive dogs. If drive dogs they would be a close fit. They are also slightly offset, therefore the balance weights integral to the shaft, can't be installed out of phase. If this is the only purpose for the tabs, then a loose fit would be acceptable.

 I imagine a scene in a board room meeting where the workers rep has a win when he says "Look, if they're only alignment tabs, they don't have to be a precision fit. Let's have a loose fit, then it's easier and much faster to assemble these units. We're going to be assembling hundreds of thousands of these"

Some of the possible causes in the K100 bulletin applies equally to the K75, since they share some of the parts mentioned. I have read some threads about output shaft noises where the solution was with the alternator or associated parts. I realise this is unlikely, but wouldn't it be good if this solves the problem without having to go into the engine.

There are some easy tests which might confirm or eliminate some of the possibilities. Here's two. 

1- Remove the alternator to see if it at least reduces the noise. 

2- Remove the crank cover, clean an area close to the tabs and slots, completely clean of oil. Put some thin paint marks on, covering both halves, and wait for it to completely dry. Assemble, ride, then take a look to see if the paint has cracked between the two parts.

better go off and do the search on the output shaft issues , discussed in the forum some 10 or more years ago

amongst some of the wear issues is the pins used in the spring tensioning of the backlash gear 


like this 


and this 




which will cause the backlash gear to loose tension against the main drive gear , thus allowing some noise at idle as each compression stroke accelerates the crank rotational speed , (  ill guess thats why bmw recommend an idle up near 900 revs ,)

also as the pins wear so does the spring at the same contact points .

ill have a pic of the spring as i get the big main bearing pulled soon ... 



and no... the early spring wasnt just too strong , it bound with the head of the rivets as it expanded after wearing out the pins and hole for the early spring  beneath that gear which resulted in a redesign to the 86 type spring (and every model of the k since )

im sorry to be the bearer of bad news , you wont be able to fix it without pulling it apart , by removing the water pump assembly and the bell housing for starters , then the whole sump has to come off to access the output shaft ..

which i have done just recently 

the rubbers shrink which lets the basket move under heavy braking and acceleration , which in turn stretches the rivets , later that action starts the rivets fretting in the aluminum body of the basket assembly , eventually elongating the aluminum holes around the rivets 

the clue to that action is seen only after removing the output shaft , you will notice a wear mark caused by the basket actually contacting the housing - body around the outer of the basket if they have shrunk enough .




more than likely you should be able to replace the pins  and that could solve early noise issues ... but look further whilst in there 


.

Charlie99/Duck:
Thank you so much for the pictures, the link, and your words of wisdom. I am torn between buying the various parts to do away with the knocking or spend my money on a larger amp to play the radio louder. I believe the answer lies at the bottom of a bottle of scotch I am working on. I’ll keep you posted.

Charlie did you remove the engine from the frame, and do you think some of the following guesses are sound?

I was going to say the rubber dampers harden and shrink because of what I've learnt from your previous posts, but was just getting economical with my words, I think it's both happening. I thought hopefully it's just bad dampers cause the noise goes away when warm, although this problem would put excessive strain on the absorber rivets. 

I was thinking the earlier, stronger, annular spring might cause the holes for the retaining tabs to grow too large, but anyway that doesn't apply in Dave's case. 

If there's no damage related to the rivets (maybe visible with the crank cover removed) on second thoughts, maybe it's not so non-urgent. So then it would be good to fix before that happens, but I spose some would say, since you're in there anyway, go ahead and replace it with the newer 12 rivet, improved absorber.

I've read a good thread on this topic that Laitch made a link to by Albyalbatross, is that the thread you're referring to?

I was guessing that a loose idle gear and annular spring would still be noisy with the engine at idle, and warm.

daveyson wrote:Charlie did you remove the engine from the frame, and do you think some of the following guesses are sound?

I was going to say the rubber dampers harden and shrink because of what I've learnt from your previous posts, but was just getting economical with my words, I think it's both happening. I thought hopefully it's just bad dampers cause the noise goes away when warm, although this problem would put excessive strain on the absorber rivets. 

I was thinking the earlier, stronger, annular spring might cause the holes for the retaining tabs to grow too large, but anyway that doesn't apply in Dave's case. 

If there's no damage related to the rivets (maybe visible with the crank cover removed) on second thoughts, maybe it's not so non-urgent. So then it would be good to fix before that happens, but I spose some would say, since you're in there anyway, go ahead and replace it with the newer 12 rivet, improved absorber.

I've read a good thread on this topic that Laitch made a link to by Albyalbatross, is that the thread you're referring to?

I was guessing that a loose idle gear and annular spring would still be noisy with the engine at idle, and warm.

yes  removed the engine from the frame as i had just striped out the clutch centre ...again ..after procrastinating about lubing the clutch splines for so long ... and many kilometers , again through many rain event travels .

thought it was about time to do Gerty's output shaft in any case whilst  this deep into the gearbox - driveline disassembly .

I think that there is more compression when the motor is cold , or maybe just more reaction of acceleration of the crank when cold  rather than warm , so is much more noticeable and possibly less oil flung around the output gearset off the crank .

i think that its worthwhile doing now rather than later , as i think that the wear patterns setup by the excessive backlash could advance the compression wear of the barrel rubbers , then stressing out the rivets .

pitty it wasnt an late 88 bike as it would already have the 12 rivet assembly 

its funny the rubbers i have seen and that i have replaced  dont follow any real service issues ...perhaps ...  maybe certain oils affect them ? or is it a production batch issue ?  along with worn backlash tensioner issues ?

in any case doing the backlash spring stuff would certainly give the opportunity to replace the inexpensive rubbers before more work needs to be done , besides replacing a 6 rivet with a 12 rivet output shaft second hand (even with low kilometers ) wont guarantee that you wont have to do the same all over again .  

yes Alby's investigations were well noticed by me and other who were active in the forum back then .

ill post up some of the things i have found between a lower kilometer 6 rivet pre 85 shaft with good rubbers and no noticeable movement on the gear to damper ...and a 12 rivet shaft that came from our mate "Rene "...(who lives just round the corner these days ) 

in fact the 12 rivet shaft has noticeable wear on the output bearing .....which is not available anywhere at the moment , unless you can find a dealer that has one on hand ...

hope that helps some .

luckily i have noticed a lot of things , having been inside there more than twice 

fortune has been on my side as i have a rebuilt motor with good 6 rivet output shaft and rubbers that i have been reassembling to go into Gerty for the time being ... 

Thanks Charlie, every time this topic comes up I learn a bit more about it.

I've got an 86 model engine, from memory it seemed like it had no signs of wear on those parts.

Some bikes would have gone many years without a throttle body balance. Also the rider might have something to do with it. Heaps of rough gear changes would be hard on the rubber dampers, I know I was hard on them, it took me a long while before I got used to gear changing on bricks (there's a lot of slop in the gear shift pedal, it's on the to-do list)

I need to find a forum where everyone only gives me good news. Okay, okay, it looks like I will be removing the frame and delving into the engine (and I thought my golden years would be spent sitting on a beach somewhere).

Are there anything (pictures, observations, etc.) I can provide for anyone while I am on my journey?

Dave

I agree with Charlie, as I said my first guess I believe the fault is at the absorber, but at this point we're speculating, and we haven't heard the noise yet, or pinpointed it's location.

There are a number of other possibilities, although unlikely, worth checking, since the tests are so easy. 


Remove the alternator, you might be lucky. 

Remove the crank cover. With a helper turning the rear road wheel in gear, stop when an absorber rivet comes into view. Now rock the wheel forward and back, if you see signs of wear, or that the rivets are loose, you have confirmed that the output shaft needs to come out. If not, you might be lucky.

Any aluminum in the oil or sump (might get your hand through the oil filter opening) 

Has your brick always had this problem, or it developed over time, or suddenly like after a service or after a hoon through the twisties.

Does the noise disappear with the clutch pulled in?

In the photo below you see a nut where the rivet was, just left of the Allen key. 



A closer view. 




So far I haven't convinced you to remove the alternator, so listen to this. Forum member Audibob removed the output shaft to fix a similar output shaft noise, we never did get to hear it though. He was understandably disappointed that he didn't find any obvious signs of wear. He put heaps of new parts in, put it all back together, and guess what, he still had the same problem. He read about other forum members who ended up in the same situation. He dived back in and reported back an improvement when he noticed the clutch balance marks were wrong by someone who previously went in there, and put it right. He still had some noise, he finally fixed it when he discovered that, guess what, the alternator wasn't installed properly.

Probably remove the crank cover first though, I spose.

Couple of observations:
I will remove the alternator this afternoon and report back.
I will post a video/audio before pulling the alternator so we have a base line.
The knocking reared its head maybe 14 months ago and has progressively gotten worse.
The bike has about 160,000 miles (it is on its second instrument cluster and has had the odometer gears replaced twice (odometer is presently not working….again).
Engaging the clutch has no effect on the knocking.
Knocking goes away as soon as the bike is underway; increasing rpm to 2000 or 2500 rpm IN NEUTRAL makes no difference in knocking - only once the transmission is under load (i.e. underway) does the knocking cease.
Knocking is not present at idle once bike is at normal operating temperature.

BTW - thanks for the detailed photos!

A microphone close up might be better at pinpointing the location than your ears (definitely better than mine) Or using a screwdriver to the alternator and the bellhousing below, the two are so close together making it difficult to tell. Maybe some other spots, like say the timing cover.

If you can see that the rivets are loose, I spose the other tests aren't worth doing.

Fuel injectors. Well, one of anyway. That's exactly how LFB behaved four years ago until I cleaned the injectors.

The first video reflects the knocking at start-up. The second video is after about 60 seconds of run time and records the knocking sound as it is affected by a change in rpm.

https://www.youtube.com/shorts/dZglvSvFRkk?feature=share

https://www.youtube.com/shorts/ElE_zq5dMxA?feature=share

I could not identify from where the knocking is coming from.

Dai wrote:Fuel injectors. Well, one of anyway. That's exactly how LFB behaved four years ago until I cleaned the injectors.

Could be injectors, I haven’t checked them since having them cleaned and spray pattern verified 5-6 years ago. I can take one at a time off line and see if there is any change I the knocking sound. I do want to say the bike is not missing (neither at start up nor at operating temperature).

I picked up a non running k1100lt (1993 ?) very cheap a couple of years ago and when I got it started it made a very similar noise. I thought for sure it was the drive rubbers on the alternator and swapped them out with good ones and made no difference. As bad as it sounds at start up I still find it hard to believe that it goes completely away once warmed up, at least on my bike. I am watching this tread to get some idea what to do next when I get some time to get back to it, so thanks for putting it on here.

caveman wrote:I picked up a non running k1100lt (1993 ?) very cheap a couple of years ago and when I got it started it made a very similar noise. I thought for sure it was the drive rubbers on the alternator and swapped them out with good ones and made no difference. As bad as it sounds at start up I still find it hard to believe that it goes completely away once warmed up, at least on my bike. I am watching this tread to get some idea what to do next when I get some time to get back to it, so thanks for putting it on here.

It's not the 6 vs. 12 rivet output shaft issue. All K1100s have the 12 rivet output shaft.

daveyson wrote:I agree with Charlie, as I said my first guess I believe the fault is at the absorber, but at this point we're speculating, and we haven't heard the noise yet, or pinpointed it's location.

There are a number of other possibilities, although unlikely, worth checking, since the tests are so easy. 


Remove the alternator, you might be lucky. 

Remove the crank cover. With a helper turning the rear road wheel in gear, stop when an absorber rivet comes into view. Now rock the wheel forward and back, if you see signs of wear, or that the rivets are loose, you have confirmed that the output shaft needs to come out. If not, you might be lucky.

Any aluminum in the oil or sump (might get your hand through the oil filter opening) 

Has your brick always had this problem, or it developed over time, or suddenly like after a service or after a hoon through the twisties.

Does the noise disappear with the clutch pulled in?

In the photo below you see a nut where the rivet was, just left of the Allen key. 



A closer view. 




So far I haven't convinced you to remove the alternator, so listen to this. Forum member Audibob removed the output shaft to fix a similar output shaft noise, we never did get to hear it though. He was understandably disappointed that he didn't find any obvious signs of wear. He put heaps of new parts in, put it all back together, and guess what, he still had the same problem. He read about other forum members who ended up in the same situation. He dived back in and reported back an improvement when he noticed the clutch balance marks were wrong by someone who previously went in there, and put it right. He still had some noise, he finally fixed it when he discovered that, guess what, the alternator wasn't installed properly.

Probably remove the crank cover first though, I spose.

I removed the alternator and the knocking sound is unchanged.

Fearing the worst, I looked at the cost of the Absorber Gear Wheel  11 21 1 461 499 and was dismayed to say the least. Then I checked what the new 12-rivet part cost and found the part number stays the same for all models through 1992. My understanding is the 12-rivet part was introduced in/after 1989; yet the part number is the same. Can you provide me with the 12-rivet part?

Dave

The six rivet unit is part 11211460903.

The twelve rivet is 11211461499.

Supersession date is 9/27/89.

Thanks!

Another point. Let's say the rubber dampers are shrunk or flogged out but the rivets aren't yet damaged. That could be seen with free play between the absorber housing and its end plate, using an inspection camera through the oil filter opening in the sump. 

I guess you might already be in there though.

If you think rubber is getting old and hardening then you can try using "High Mileage" motor oil which has additives to recondition rubber.

I currently use a 50/50 mix of Mobil 1 15W-50 and Mobil 1 10W-40 High Mileage in my Ks. My theory/hope in doing this is that the rubber additives in the high mileage oil will help keep the clutch nut O-ring, main seal and water pump seal from failing.

I will use the high mileage oil in the event the rubber dampers are hardening.

It seems the knocking is the result of worn rivets and/or hardening rubber dampers. The cost of addressing the worn rivets is very steep ($800) and since the knock is non-critical, I am not prepared to pull the trigger on this now (or possibly ever).

At this time I will hold off addressing this knocking until such time as I run across a newer K with a 12-rivet absorber being parted out.

Dave

There's no need to buy a new one. Keep your eye out on Ebay for a used output shaft from a K1100. The K1100s came with the 12 rivet 11211461499 output shaft. Be sure to check the pictures to make sure that it's got 12 rivets. You should be able to get one for less than $100.

Can you see or feel looseness in the rivets, or free play with the absorber housing?

If not, the problem might be elsewhere.

It would be great to find a used one for $100. I wasn’t able to see any slop with the rivets but that should not be construed as they are fine. The rivets are difficult - at best - to see.

I will start watching EBay for the part.
Dave

davemadsen wrote: Then I checked what the new 12-rivet part cost and found the part number stays the same for all models through 1992.

The part number stays the same for all models because production of the six-rivet part ended when it was replaced by the 12-rivet part—with its new part number—for all models.

Thanks!

davemadsen wrote: I wasn’t able to see any slop with the rivets but that should not be construed as they are fine.

True, but not finding any damage should not be construed as they are damaged.

So shrunken rubber dampers are still on the cards (amongst others) A mirror and torch might do the trick.

Caveman, I was hoping Dave would say that the noise disappeared with the clutch pulled in, but it wasn't to be. Does yours disappear with the clutch pulled in?

 Edit; and does it disappear when the engine is warm?

Caveman, it just dawned on me your bike is a late model K (post 1989) and therefore should have the 12 rivet absorber gear which is god’s answer to the 6 rivet knocking sound. This being the case, it will be interesting to hear what solves YOUR knocking sound.

davemadsen wrote:I wasn’t able to see any slop with the rivets but that should not be construed as they are fine.

Charlie99 is the experienced head in this matter but my observation is that your gear doesn't have rivets at all. Those have already failed in your Bricks gear and have been replaced with bolts and nuts—a not-unheard-of and successful remedy in some cases I've read. What's in there certainly doesn't have the profile of original rivets whatever they are. Maybe somebody can clarify for me what's in there.

Yours


BMW's

Laitch your right, the rivets have been replaced with bolts in that photo. Because Dave quoted me, my photo is on Dave's post. That photo is of my spare engine.

daveyson wrote:Laitch your right, the rivets have been replaced with bolts in that photo. Because Dave quoted me, my photo is on Dave's post. That photo is of my spare engine.

It's always a thrill to be right when I'm wrong.

Now my pronouncement is the the output gear rivets aren't the problem.

Once you get down to the clutch basket  , its pretty easy to tell if the rivets are elongated holes   .  Even with bolts as a replacement , and once removed saw the actual extent of  movement   the clutch basket is a good indicator to what may be inside,   think i saw about 7 - 8 mm of  clutch basket moovement to fractions of buffer drum slop... and you can hear anti backlash wear   .   
Just a heads up