My K100RS make some grinding noise when pulling off from stand still or when accelerating from lower speed. And it feels a lag of power delivery as well. But once go beyond 3000 rpm, this feeling goes away. Moreover, when in natural, if i turn the throttle fast, there is a rattling noise as well.

I guess the output shaft may be the problem, as i am going to change the clutch, I probably will change it as well. 

My bike is K100RS, document says it was made in 1986 (the year when BMW replaced 6 rivet with 12). However after data checking with Motorworks, they say my bike was made in 1985 in the factory and thus should come with the 6 rivet output shaft. 

As I am ordering parts, should I buy a original 6 rivet output shaft? Or should I upgrade to 12 rivet? What modification and extra parts will I need?

Thanks a lot!

First thing to check is the simplest and cheapest. Check the alternator rubber "monkey nuts" are okay first (if you haven't already done so).

No mods required to switch from the 6 to the 12.

hi again billy

in my opinion the jury is still "out" on this issue

we have evidence of good output shafts still making noise  after refurbishment of all the bits around them and no measureable movement at all in the output shaft rivets

there does seem to be some debate about the thrust washer between the output shaft bearing and clutch cluster and output shaft locknut ...which on some models seems not to be installed ...(or has it broken up and just vanished over the years )

many bikes run well with the noise apparent ...its just at startup (cold) that it appears more apparent
 
I believe the 16 valve models have the 12 rivet shafts  so you should be able to get a bottom end or replacement from a parted out 16 valve motor .
having said that there are still procedures for checking if there is movement on the shaft ...which can be done by removing the bottom end crank cover (rhs )  and viewing the mechanics without taking it all apart

have fun

charlie99 wrote:hi again billy

in my opinion the jury is still "out" on this issue

we have evidence of good output shafts still making noise  after refurbishment of all the bits around them and no measureable movement at all in the output shaft rivets

there does seem to be some debate about the thrust washer between the output shaft bearing and clutch cluster and output shaft locknut ...which on some models seems not to be installed ...(or has it broken up and just vanished over the years )

many bikes run well with the noise apparent ...its just at startup (cold) that it appears more apparent
 
I believe the 16 valve models have the 12 rivet shafts  so you should be able to get a bottom end or replacement from a parted out 16 valve motor .
having said that there are still procedures for checking if there is movement on the shaft ...which can be done by removing the bottom end crank cover (rhs )  and viewing the mechanics without taking it all apart

have fun

I have seen some opinion saying that the circular spring between the thin and thick gear ( the anti back lash mechanism ?) is the source of the noise. Not sure.  Here's the link i found:
http://hrsbstaff.ednet.ns.ca/bvogel/K100/K100.htm

BTW, not only the noise is bothering me. I can feel a lag of power delivery while that noise is happening, mainly when pulling off or accelerating from lower rev, when torque transfer is large. As my clutch is not yet slipping, seem I can only blame the output shaft assembly. Or perhaps anything in the rear part of the transmission?

Also, although my clutch is not slipping yet, the actuation is very stiff, and the biting point is very narrow. So, I think the clutch is probably almost at its end. And the service history suggested that the clutch perhaps hasn't been replaced since leaving the factory.

yes likely is the clutch plate with the extra explanation

but a review of the clutch activation mechanism is also warranted

we have seen lots of clutch actuating arm bearing siezures  and cable issues that may be contributing factors


but do as mike p suggests whilst your doing that work ...the (monkey nuts) rubbers  in the alternator bell housing


good luck

duck wrote:No mods required to switch from the 6 to the 12.

Thanks. How about the needle bearing and main bearing? All same?

  you guys opinions are so valuable! This is my first older BMW, and many things are so different from today's main stream bikes  

charlie99 wrote:yes likely is the clutch plate with the extra explanation

but do as mike p suggests whilst your doing that work ...the (monkey nuts) rubbers  in the alternator bell housing

good luck

billy_k100 wrote:

duck wrote:No mods required to switch from the 6 to the 12.

Thanks. How about the needle bearing and main bearing? All same?

I'm pretty sure they are but you'd probably want to double check part numbers at RealOEM or some other online fiche.

According to the write-up at IBMWR (http://www.ibmwr.org/ktech/output-shaft-noise.shtml) a bad output shaft causes noise at higher RPMs.  As suggested earlier, I'd check the alternator monkey nuts first as that is pretty easy to do and inexpensive to replace. (about $20 for a set of three in the US)

duck wrote:

billy_k100 wrote:

duck wrote:No mods required to switch from the 6 to the 12.

Thanks. How about the needle bearing and main bearing? All same?

I'm pretty sure they are but you'd probably want to double check part numbers at RealOEM or some other online fiche.

According to the write-up at IBMWR (http://www.ibmwr.org/ktech/output-shaft-noise.shtml) a bad output shaft causes noise at higher RPMs.  As suggested earlier, I'd check the alternator monkey nuts first as that is pretty easy to do and inexpensive to replace. (about $20 for a set of three in the US)

Can you please suggest any source to find OEM part list for K100? I have been searching but couldn't find it  . . .  

I definitely will check the alternator first.  "monkey nuts" are they the rubber dampers of the alternator?

billy_k100 wrote:

duck wrote:

billy_k100 wrote:Thanks. How about the needle bearing and main bearing? All same?

I'm pretty sure they are but you'd probably want to double check part numbers at RealOEM or some other online fiche.

According to the write-up at IBMWR (http://www.ibmwr.org/ktech/output-shaft-noise.shtml) a bad output shaft causes noise at higher RPMs.  As suggested earlier, I'd check the alternator monkey nuts first as that is pretty easy to do and inexpensive to replace. (about $20 for a set of three in the US)

Can you please suggest any source to find OEM part list for K100? I have been searching but couldn't find it  . . .  

I definitely will check the alternator first.  "monkey nuts" are they the rubber dampers of the alternator?

Yes, on the monkey nutz - when you see them you'll know why.

http://www.realoem.com/bmw/partgrp.do?model=0511&mospid=51747

http://www.ascycles.com/Illustrated_catalog2/MicroList.aspx?id=51752

http://www.maxbmwmotorcycles.com/fiche/PartsFiche.aspx

And there's lots more out there.

And if you want to know when your K100 was built: http://www.bmw-z1.com/VIN/VINdecode-e.cgi

Thanks so much 

The original schedule was to drop the engine, inspect the transmission train and replace the clutch. 

If now need to inspect the output shaft assembly as well, what might be the list of extra works?

As I don't have a workshop myself, I need to convince my mechanic to do it ..:| 

I guess:

- strip down engine accessory so that the engine can be flipped over upside down
- water/ oil pump off (need to put on new gasket when re- assembly I think ?)
- Oil pan off (need new gasket or just sealant?)
- engine bottom cover off  (again need new gasket or just sealant?)

Thanks  a lot

No gaskets, just sealant.

aye !!

get some dreibond 1208 .sealant .....bloody marvellous stuff

you don't need much ...just a smear ....

good luck !

billy_k100 wrote:My K100RS make some grinding noise when pulling off from stand still or when accelerating from lower speed. And it feels a lag of power delivery as well. But once go beyond 3000 rpm, this feeling goes away. Moreover, when in natural, if i turn the throttle fast, there is a rattling noise as well.

I guess the output shaft may be the problem, as i am going to change the clutch, I probably will change it as well. 

Hi there, did you revised the drive shaft splines and final drive gears. My clutch once slipped and the failure´s sympthoms were the feeling of lack of power under acceleration and the engine´s revving increase without gaining speed. No grinding noises.
Hope this helps.
Best regards
JAP

a very good point jap

japuentes wrote:

billy_k100 wrote:My K100RS make some grinding noise when pulling off from stand still or when accelerating from lower speed. And it feels a lag of power delivery as well. But once go beyond 3000 rpm, this feeling goes away. Moreover, when in natural, if i turn the throttle fast, there is a rattling noise as well.

I guess the output shaft may be the problem, as i am going to change the clutch, I probably will change it as well. 

Hi there, did you revised the drive shaft splines and final drive gears. My clutch once slipped and the failure´s sympthoms were the feeling of lack of power under acceleration and the engine´s revving increase without gaining speed. No grinding noises.
Hope this helps.
Best regards
JAP

yea, I also don't think my clutch is slipping too. The drive train is a worry, because they hasn't been dissembled for inspection for many years according to repair history.

So the original schedule was to drop the whole lump, inspect the drive train, renew the clutch and clutch actuation parts. But after I done some online research, the output shaft may also be a reason of the noise.

Hope the final drive and spines are fine, otherwise it would be very expensive 

forgot to say, my bike's grinding noise seems to be more obvious when warm. 

a summary of the noise:

-  clutch is not slipping, but biting point is very narrow
-  the clutch lever is very stiff (probably the clutch actuation part's problem)
-  grinding noise when pulling off from stand still, accelerating from lower rev, or going up slope with lower speed. Basically whenever the drive train is loaded with heavier torque. 
- Noise disappear beyond 3000 rpm. The bike sounds nice and healthy after 3000 rpm indeed. 
- Noise also appears, but less obvious, when engine braking (closing throttle)



So now the possibilities are:

- alternator monkey nuts
- worn clutch
- output shaft
- drive shaft failure 

anything else? I read a early post here saying the uni-joint, does that mean the uni-joint of the drive shaft?

any chance that the grinding noise is from the final drive (some call it differential) ?

Checked gearbox and final drive oil, fresh and level correct.

I would start with the drive shaft, and the final drive, then the alternator.
If the drive shaft is not at fault think that a proper splines lubrication is in order.
Good luck
JAP

Even if it is the countershaft rivits worn and making a noise you will still need to remove the drive and gearbox to get to it, so you may as well start with an inspection and rebuild whatever needs it.

RicK G wrote:Even if it is the countershaft rivits worn and making a noise you will still need to remove the drive and gearbox to get to it, so you may as well start with an inspection and rebuild whatever needs it.

Agree, the plan is to dissemble and inspect all the way up from the final drive to the clutch assembly 

Spine damages should be easy to observe. For the drive shaft uni-joint and final drive failure (pinion gear and ring gear, or other things), what signs should I look for ??

japuentes wrote:I would start with the drive shaft, and the final drive, then the alternator.
If the drive shaft is not at fault think that a proper splines lubrication is in order.
Good luck
JAP

Am I looking for excess play at the uni-joint? and wear at the spines?

billy_k100 wrote:

japuentes wrote:I would start with the drive shaft, and the final drive, then the alternator.
If the drive shaft is not at fault think that a proper splines lubrication is in order.
Good luck
JAP

Am I looking for excess play at the uni-joint? and wear at the spines?

Hi, you are looking for play at the uni joint and wear (including metallic debris) at the splines, specially at the aftmost one. Also for the final drive play an metalic debris in oil.
Regards
JAP