My 1991 K75RT (126000 km) has developed a bad clattering sound between 3500 and 3700 rpm in all gears. It’s as if someone was hitting the ‘inside of somewhere’ with several hammers. Running on the flat and level in that rpm range it is not noticeable but if the road gradient increases in that range, putting a greater load on the engine, the noise starts. It also starts if I accelerate slowly up through that range. It is not there during a rapid acceleration through that range. 
I’ve gone through a number of the threads in this site on engine/alternator noise and have followed much of the good advice I’ve come across. Here’s what I’ve done so far.

The first thing was to change the alternator’s rubber shocks (monkey nuts) although the old ones didn’t appear to be particularly worn. I also changed the brushes as they were at their limits. On reinstallation of the alternator the noise was still there. 
Took the alternator out again and changed the bearings (which were worn) and did a general cleanup. On re-installation the noise was still there. It may be a little less noticeable but possibly only because I’d like it to be. 
In order to be able to try to home in on the noise I had hoped to get it to appear with the bike running while on its centre stand, in gear, in the rpm range, and with the rear brake dragging to try to replicate being on the road. No success. 

Next step was I took the alternator out and ran the bike without it. The noise was gone!

However, I don’t quite see how such a noise could be coming from the alternator, particularly after it had been serviced. I had a look at the timing chain a couple of years back and it was in pristine condition so I don’t think it’s that. My thoughts are, and they’re based on the info I’ve read on this site, that it may be coming from the auxiliary alternator drive. Could it be that without the alternator installed there isn’t the load on it to cause it to make the noise?

There was a thread started about a year ago that sounded similar to my situation but the final outcome was never posted.
The sound in this youtube reference:     www.youtube.com/watch?v=LdSNT4WPxBc        sounds very much like my problem. Not the spinning sound, but the metalic ‘clank’ that’s generated.

As I’m feeling reasonably sure, well, sort of sure, well, I’m not really sure, it’s not the alternator I guess I have a winter project ahead of me. 

Any thoughts or advice on the above would be greatly appreciated!

If the general concensus is that it may be the alternator drive, taking the final drive/transmission/clutch out is not an issue as I’ve done it a number of times to grease the splines, but can I get to the alternator drive without removing the engine? That seems like a pretty daunting task to me.

Once again, any thoughts or advice please.

Goodonya! Interesting that you've managed to isolate the noise through persistence.

In order to access the alternator drive/sprag clutch mechanismo the 'bell housing', or intermediate section, needs to be removed. This requires at the very least that the gearbox is out of the way, as you already know. I was easily at mine with the gearbox out and the frame bolted to the engine at the front - of course the rear bolts and the upper right hand side bolt (rear) need to be removed.

I simply supported the engine and rear part of the frame and accessed the works without removing anything forward of it.

You say the noise developed but can you tell us more about the rate of development. Has it got worse since you first noticed it?
Please excuse me being the one to ask for confirmation the the arrival didn't coincide with alternator having been removed for some other reason. I managed to put mine back in with the monkey nuts incorrectly placed on one occasion. Unlikely I know, as you would have had to achieve this fopar three times in a row!

TWB, Thanks for the info. Comforting to know it’s not a bear to access. I’m not really sure that I’ve actually isolated the noise though. When you went into your alternator drive were you chasing a noise and was it like what I’m experiencing?

Rawdonball, the noise started on an instant, not a slow progression over time. Nothing unusual in my handling of the bike prior to it starting but it was a run in the mountains with lots of gear changing. It was so disconcerting that I didn’t think I would make it home. I’ve since put on a cautious thousand km since it started with no noticeable change or  worsening of the noise. Please don’t hesitate to ask questions like misinstallment of the monkey nuts. I appreciate any and all questions as so many problems can be traced to a simple error. God knows I’m not immune from making them. I think I own the cornerstone in that department! To answer your question though ... no, I’m confident they’re installed correctly as I had noticed someone’s comments about that in a thread about alternator overhaul before I did the work and was careful not to make the mistake.

Before you pull the bike apart try some of the simple tests, tape up or check that the clutch arm isn't rattling on the exhaust or stands, that sort of stuff.

Exhaust heatshield. Once the anti-vibration mount at the front falls off (and they all do), it gets as annoying as hell at certain revs. I took mine off in the end.

It would be interesting to know whether the noise is affected by current draw to head light / heated grips etc - i.e. when the load on the alternator and hence the torque transmitted by the drive is varied...

I have the same problem with my K75 and have done all that stuff too.  Right now I am planning to go into the intermediate section this winter. 

From what I have been able to learn on the interweb, the noise is probably related to the anti backlash spring on the output shaft.  When this spring wears and/or gets weak, the backlash gear on the output shaft is able to rattle around inducing a clanking sound  at specific engine speeds.  On my bike it's at 1800 to 2000 rpm.  While it's not the same speed yours rattles at, it is interesting to note that yours is rattling at around the second harmonic of mine.

Good thoughts, but I’ve prodded and poked all over the bike in hopes of finding something loose, or out of adjustment and touching something else. Nothing. The muffler cover on the K75 is different from the K100 and doesn’t have an anti-vibration mount.

Point Seven Five, I’ve pretty much decided to go into the intermediate housing as well and look at the alternator drive. Is the anti-backlash spring on the output shaft also accessible with that housing off? I’m unable to figure that out from exploded diagrams of the engine.

I'm not sure if you can reach it from the intermediate section, but I  am going to check that out first before dropping the engine and removing the oil pan.

With all the crap that is jammed in between the engine and the tank it doesn't look like a fun job getting it back into the frame.  Not something I want to do with my limited shop facilities.  I've been told it's not that hard, but based on my experiences with air filters, color me highly skeptical.

Point-Seven-five wrote:I have the same problem with my K75 and have done all that stuff too.  Right now I am planning to go into the intermediate section this winter. 

From what I have been able to learn on the interweb, the noise is probably related to the anti backlash spring on the output shaft.  When this spring wears and/or gets weak, the backlash gear on the output shaft is able to rattle around inducing a clanking sound  at specific engine speeds.  On my bike it's at 1800 to 2000 rpm.  While it's not the same speed yours rattles at, it is interesting to note that yours is rattling at around the second harmonic of mine.

I had this exact same issue in the first few months I owned my bike. While moving off in first gear at around 2k rpm I'd get that loud clatter. A local retired BMW m/c mechanic reckoned it was the backlash spring and it wasn't a big issue. A while later I noticed the noise had disappeared. That was very welcomed because it annoyed the hell out of me. At the time the only things I had done to the bike that may have affected the engine  was change the engine oil and replace and adjust the clutch cable. 
I was very new to the machine and didn't realise that the clutch was way out of adjustment due to the cable being badly frayed at the handlebar lever nipple.
When I changed the oil I found it to be very black and thin even tho the PO told me it had been changed recently.

Just a thought
Hope you find the problem.

Kaptain, Can't speak for the other poster, but mine clatters right after oil changes with 20W-50.  Been doing it since I got her about 18,000 miles ago.  Wish mine was that easy to fix.

Hi .75
How long does yours clatter for after the engine oil change?

Fresh oil, old oil, cold engine, hot engine, no load, loaded, doesn't matter, it clanks.

Doesn't seem to hurt anything, just makes an otherwise nice bike sound like a piece of crap.

I get you...

I have my '86 K75C in pieces at present even though it wasn't clanking. It's a high mileage machine (over 200k km) and the only degradation I have been able to identify is that the backlash gear does not rotate freely relative to driven gear when I try this by hand with just these two components (C spring etc removed).

The pic below shows the annular contact surfaces as shiny rings just inboard of the gear teeth root profiles. This particular gear set was off a friends later model K75S (240k km) which was reported to be clanking at a rev range around 3000 - if I remember rightly. The same notchy feeling described above was found to be due to uneven wear on the contact surfaces - i.e. less wear on the driven gear contact surface at points adjacent to each root (between two gear teeth) with these 'high points' corresponding with dips in the back lash gear contact surface. The situation that develops seems to be something like the indexing that occurs with worn steering head bearings.

My theory is that the wear pattern occurs due to variable hardness levels on the periphery of the driven gear contact surface which is a product of case hardening of the gear teeth during manufacture. The backlash gear doesn't transmit load to the same extent so I assume that its teeth are not case hardened.

For the K75S we used a piece of glass and valve grinding paste to get the backlash gear face back to plane (semi) and then used this to lap in the mating face of the driven gear. Unfortunately this process couldn't be completed due to other commitments, bike went back together in a rush and the clattering problem persists - albeit to a lesser extent...

Very interesting post rawdonball. The coin has finally dropped for me regarding the purpose and functioning of the backlash gear. 
On your friend’s K75S did you find any problems with that other potential ‘rattle-clunk’ culprit, the alternator auxiliary drive? (Still trying to decide my full course of action on the winter project)

Possibly a championship dumb question, but since the anti-backlash gear doesn't appear to be transmitting any of the engine's output, what is the difference between running with it loose and not functioning and not having it there at all?

Could it be the mechanical equivalent of an appendix?  A case of Teutonic over engineering?

Mr Rhodes - I was amazed how good everything looked on the 75S with its 240k km. Not a hint of any bearing or tooth or thrust related problems on the aux drive.

0.75 - importance of the backlash gear is one that really interests me. Someone on here claimed that he had simply removed the gear and suffered no ill effects...
I looked at this possibility and would be reluctant to try it because there is a drilling in the output shaft to allow oil into the space between the back lash and driven portions of the compound gear arrangement - presume this is the main source of lube for the mating of crank and output shaft gears and is likely to be impaired if replaced by a rotating squirt!
Also - possible redistribution of oil flow volumes (increased oil to the squirt through less resistance will reduce flow elsewhere?)

I believe BMW had at least one go at overcoming the clatter problem on the 75 - the replacement of the basic cir-clip on the clutch end with a unit having sprung tabs (controlled end float). The 75S has this mod so seems it didn't solve the problem.

They have been known to give up on design aspects that were later considered to be more hassle than they were worth? Vacuum switch to provide additional signal to FICU????

Don't forget that initially there was a 'spring-disk' arrangement pushing both gear wheels together which was later replaced by a fitted spacer ring. What was the arrangement in place? If you 'grind down' the wheels at their mating surface you might need a thicker spacer ring.

My '86 75C has the 'spring disc' and the 75S of the Mates was the later arrangement where they have the simple spacer but the more complex cir-clip.

On the 75S the end float was below the minimum allowable specified so we did some lapping of the spacer in addition to what was removed from the gear faces.

I’m about to change the anti-backlash spring in my ‘91 K75RT in the hopes it will resolve the noise mentioned in previous posts. The bike is torn apart up to, but not including, removing the lower crankcase half to get at the output shaft. Before I do that I’m waiting for parts so I’ll have them on hand while doing the surgery. 
There’s a tool (BMW # 12 4 600) needed for the 75's to refit the anti-backlash gear (on the 100's the tool apparently is not really necessary). I have no idea what it even looks like. Has anyone fabricated one of these tools, and if so can you give me an idea about what’s involved so I can make one up and have it ready for when I need it?

I know we got ours back together without the assistance of any special tools...

Thanks rawdonball. That's encouraging.

I’ve opened up the anti-backlash gear assembly (‘91 K75RT) and found very little wear on the anti-backlash spring. There is some wear on the anti-backlash gear face from the shim. The original shim is 1.12mm thick (a little thinner in places where it too has worn). Upon reassembly (as you said rawdonball, not difficult) I find it very difficult to tell whether the inner bearing race sat directly on the shim or on the drive gear bearing boss. I will be replacing the shim, the closest available size to the original being 1.15mm, in which case the bearing will definitely sit on the shim. Is this how it’s supposed to be? Haynes only says to fit a shim to eliminate the clearance between the gear and the bearing.

I have just taken my 1994 K75RT apart to do the backlash spring, and much to my dismay have found that all is perfect and there is no discernible wear. 

What I did find was that there are two tabs on the output gear that fit into slots machined in the output shaft.  The fit is very sloppy and appears to be intentional.  It allows the gear and the shaft to move relative to each other, and when I move them on my bench they make the clanking sound that is so annoying at idle and accelerating away from a stop.



It appears that the only thing keeping these two parts from moving is the friction between their faces and the force applied to those faces by the torque on the clutch nut.  Why the heck would BMW design such a sloppy fit and then do practically nothing to keep the parts from banging around besides the torque and the length tolerances on the shaft and the spline hub of the clutch housing? 

I have been thinking about this for the past three days and the only reason I can come up with for doing this is to implement some sort of dynamic balance to fine tune out the engine vibrations.  I surmise that when properly torqued the vibration of the engine will adjust the position of the balance shaft.  At that point, the friction between the shaft and the clutch spline hub will hold it in place until engine vibration causes it to move again.

After a number of miles, a very slight amount of wear or sloppiness from metal fatigue appears and the relationship can no longer be maintained, allowing the shaft to freely move in relation to the gear.  At low engine speeds the vibration frequency is low enough to allow the tabs to swing back and forth in the slots causing the clank.  As engine speed increases the inertia of the shaft no longer allows enough time for the tabs to swing the full gap in the slots and the clanking stops.

So there it is.  It looks to me like the only recourse is to just make sure the clutch nut is torqued to the highest specified torque and to periodically(probably when doing a clutch spline lube) retorque that nut. 

I hope that Inge and Rob read this and comment.  I would be very interested in their thoughts.

I’m at the same stage as you Point Seven Five. The gap between the tabs and the shaft appear to be the same as yours, ~ 1/32". All I’ve managed is to do is shrug and begin the reassembly process.

Oh, one other thing .. I’ve started to write a book about this. I’m calling it “50 Shades of ‘K’ ”. It’s a long roller coaster of a story, filled with frustration, interspersed with wild moments of self-flagellation.

Any thoughts on shim thickness?

I think your on the money for the source of the noise .75, being the tabs of the driven gear to the output shaft

this is exactly the place that the k100 develops the same noises (although through a different mechanism )

consider the fact that there is a slight deceleration and then a high acceleration of the driven gear as each piston goes through compression then firing

the inertia of the clutch flywheel keeps the whole output shaft at more or less the same speed during these events, letting the tabs whip around forever wearing the small gap to a larger one .

probably more noticeable whilst the engine is cold

whilst the shims etc keep the gap constant between the driven gear and the anti rattle gear and are quite important,    i feel that the tabs you have highlighted are the source of most of the noise.

just some thoughts

Charlie, At first I thought the gap may have been the result of wear, but close inspection of the tabs and slots doesn't reveal any noticeable wear.  The contact points are pretty hard.  If anything, my fear is that the tabs will eventually break off.  This would allow the balance shaft to just spin and make the engine vibration really bad, not to mention two chunks of hardened steel floating about in the crankcase. 

Am hoping that someone can chime in with some good information on the original design intent. 

Does anyone know if BMW issued a service bulletin on this noise?  Judging from the number of people who report having it on their machines I would think the factory had to be made aware of it some time in the past.

I've just had another look at my K75c ('86) to refresh my memory. I can't see any evidence of wear ion the contact faces of my driven gear dogs. The mates k75s with 250k km looked and felt the same in this regard. Looking at it now, I'm reminded that the forged counter shaft with the weights, doesn't actually transmit any of the drive torque between engine and back wheel - if the dogs were removed, only the counter balancing action would be lost. 
I think it must be Clymer manual which gives more info on the clearance/end float to be obtained by selecting appropriate shim when assembling anti backlash gear and the bearing which locates the assembly.

"Looking at it now, I'm reminded that the forged counter shaft with the weights, doesn't actually transmit any of the drive torque between engine and back wheel"

True, but don't forget the pumps(water & oil) at the front of the engine.


"I think it must be Clymer manual which gives more info on the clearance/end float to be obtained by selecting appropriate shim when assembling anti backlash gear and the bearing which locates the assembly."

I'm not sure, but end float is probably more important in minimizing the side loading and the subsequent wear on the bearing that supports the drive gear.  The clanking appears to come from radial float of the balancer shaft.  The dogs aren't intended to transmit torque, but are there to limit that radial float of the balancer shaft to keep it roughly in sync with the crankshaft.  It's the relatively loose balancer shaft hitting those dogs that causes the clank.

Of the owners with the clank, how many have had the clutch nut off to replace the o-ring and seal?

At this point I am pretty sure the noise is the result of insufficient friction between the end face of the spline hub and the face it contacts on the balancer shaft.  I wonder if oil got in between those faces when the previous owner of my bike removed the clutch nut to replace the o-ring.  Removing that nut removes the force holding the faces together and probably allows oil to flow between them.  That tiny bit of oil is probably enough to drastically reduce the friction and ultimately allows the balancer shaft to move around a lot more than it was intended to. 

When I reassemble my engine, I'm going to be very careful to have those faces spotlessly clean and free of oil.  Future service that requires removing the clutch nut will be done after draining the oil and letting the engine drain for a day or two to minimize the oil that might get into that joint.  At my age, and with the miles I put on my bike there is little chance that nut will ever come off again while I am around.

Point-Seven-five wrote:"Looking at it now, I'm reminded that the forged counter shaft with the weights, doesn't actually transmit any of the drive torque between engine and back wheel"

True, but don't forget the pumps(water & oil) at the front of the engine.

sorry to pipe up and disagree most strongly

it is called the output shaft and directly transmits all torque from the crank through the output shaft to the clutch basket at the rear of the engine
the whole concept of the output shaft is to counter act all torque twisting action of the crankshaft with a directly opposite revolving torque

it is a necessity that the ratio of exactly one to one and lends itself as a good counter balance to the timing of the three cylinders vibrations inherent in 3 pot / 4 stroke designs  ...you might remember than many engines use a chain to a counter shaft for such tasks ...but due to good design not so in the k bikes

Charlie, you are one of the most knowledgeable posters on this forum, but in this case I must respectfully disagree.

Engine torque travels through the output gear to the clutch basket through splines inside the gear and the outside of the clutch basket hub.  The "output shaft" with the counterweights transfers no torque to the clutch, rather it just goes along for the ride coupled to the clutch basket hub only by the friction between the faces of the shaft and the hub and the compression ring on the hub at the front. 

The dogs on the gear and the mating slots in the shaft only limit the motion of the shaft relative to the gear, allowing some small amount of dynamic balancing while preventing the balance weights from getting out of sync with the crankshaft.  If they were indeed meant to closely couple the shaft to the gear I am pretty sure the BMW engineers would not have left the large gap in the fit. 

True, the shaft does provide dynamic balance to counteract crank vibrations, but it also transfers a small amount of the engine torque to the pumps at the front of the engine.  The power required is low enough that the friction coupling between the shaft and clutch hub is adequate for transmission.  As I mentioned above, it appears to me that the clatter is the result of the friction between the parts decreases over time and allows the shaft to move relative to the gear allowing the dogs to bang against the sides of the slots causing the clank. 

I'll admit it's all theoretical right now, and I would really like to see if there is some sort of comment from the factory via service bulletin.  In the meantime, I will make sure the clutch hub nut is torqued properly and the faces are as clean of oil as I can make them before assembly.  I should have everything together and the engine running in about two weeks.  I will report on if the clank issue has been resolved at that time.

I think you are talking at crossed purposes. The counter weight does not form part of the shaft but slips on and is located by the two dogs. The torque is transmitted to the clutch basket by the gear which is fixed to the shaft and will not move in relation to the shaft however the shaft does not transmit the torque the gear does that.
Maybe thats as clear as mud now.
One thing I will say is that I don't believe the noise made by the interaction of the shaft and counter weight could be described as a clank in any way, if they did in fact make any noise I would say a low level thump would best describe it. I personally think you .75 are looking in the wrong place but unfortunately I don't have any suggestions. Also I don't think that an oil free friction surface could be maintained over a lengthy period to be worth considering it as a damping method for the counter weight.
I looked at that counter weight and the dogs and immediately thought NO that isn't where any noise is coming from or there would be damage, however I do agree with your saying that the gap and free play is for the fine tuning which does happen just by the nature of ballance weights, the same as mud will ballance a wheel by collecting on the inner part of the wheel so as to counter any out of ballance, Dyna beads work the same way.

RickG, I agree the play in the dogs seems to have some sort of dynamic balance function.  You must be hearing something different because when I rotate the shaft so the dogs hit the edges of the slots the sound is exactly what I hear between 1200 and 2000 rpm.

With 100 lbft on the clutch nut the friction between the faces should be substantial and should only allow limited movement, and the faces should be tight enough to not allow oil in after assembly.  Since the previous owner serviced the rear main seal and the o-ring he must have removed the nut and allowed the faces to separate letting oil lubricate the surfaces.  If he did not torque the nut enough the combination of oil and less pressure on the faces could be the source of the motion that is causing the clanking.

Of course, right now it is all speculation.  But since I was unable to find any thing amiss in there, specifically the idler gear spring and all the bearing for the starter and alternator are ok, only reassembly with dry faces and the proper torque will tell if I have found the problem and corrected it.  Should be inb a week or so when I reassemble after getting new seals and o-rings.

must admit I was referring to the k100 ...as this is what i have experienced before ....to me the diagrams looks as though the clutch basket fits to the output shaft splines ....had no idea the k75 would have been different ...it doesn't seem to be in the manual ...but maybe haven't explored this fully

please accept my apologies

charlie99 wrote:must admit I was referring to the k100 ...as this is what i have experienced before ....to me the diagrams looks as though the clutch basket fits to the output shaft splines ....had no idea the k75 would have been different ...it doesn't seem to be in the manual ...but maybe haven't explored this fully

please accept my apologies

Charlie, No problem.  A good chunk of what I know about Bricks I have learned from your writings here.  The discussion here is about a part of the bike very few have an opportunity to experience first hand,  Add to that the fact that this one of the few areas where the design of the two engines differs so I guess it's easy to get confused.

I am only trying to add to the knowledge base surrounding a part of the engine that doesn't seem to have a lot of information.

you've given me an inspiration to chase this up a little more
I'm thinking it would be great to do away with the damper basket in the k100 ...
yes this blooming thing


lets see  what can happen eh ?

I'm waiting for you guys to get to the bottom of this because it has me intrigued.  My old girl used to clank like that when taking off in 1st and 2nd when I first got her but about a month later the noise disappeared.
I did a lot of maintenance at that time but one thing which may have altered the state of affairs inside the engine was the PO had over filled the sump with nearly a litre of oil. That may be of particular interest to you Point Seven Five.
Cheers

The oil overfill is interesting.  What I would like is to hear from owners who have had the noise start after doing an o-ring or seal replacement, especially if it was on a K75.  The really good news is that if I am right and this is really the cause, the fix should be relatively easy.  You wouldn't need to do more than remove the clutch basket and clean the oil from the face of the shaft with brake cleaner.  Could be done with the engine in the bike as sort of an enhanced clutch spline lube.

On other fora they determined that the buzzing noise was a result of the 'spring ring' having resulted in wear in the holes in the gear wheels and therefore no longer properly tensioning the gearwheels together, as well as the trapezium ring to be replaced with a proper spacer ring, tightening it better together.

If you doubt the clearance between the notched balancing part and the gear part you need to look at how it is supposed to be 'clamped in' on both ends. I doubt the parts are expected to move relative to each other, as that would create an uncontrollable friction, which I suspect can't be controlled over the bike's lifetime. But I'm happy to learn about that :-)

I appreciate the differences with the K75 and its balancing shaft, but the arrangement around the idle gear is the same.

With regards to the shimming the BMW manual clarifies that the bearing rests against the shaft and not on the shim:

Dimension A              Shim

1.60mm - 1.75mm      1.60mm
1.76mm - 1.90mm      1.75mm
etc. where Dimension A is the distance from the idler gear to the bearing seating surface.

I wouldn't know why you would want to loose the vibration damper on the K100? Charlie, just clean it and put it back! :-)

I've been watching this thread for some time with interest. I have a K100 basic with under 4K miles (seriously) and it's lovely and quiet as should be expected with such a low mileage. I also have a K1100lt with 39K showing and it's a bit harsh and grumbly at times from the intermediate gear.
I also have a K100 8 valve track bike and in the interest of lightening engine internals, I run the bike with no intermediate gear and it's really smooth and quiet at all RPM-go figure!

Mike, when you say intermediate gear, do you mean the starter gear?  Do you push start?

Update:  As I get into the reassembly of the engine I have been looking more closely at all the parts in the intermediate section and I have found a few more things that escaped notice on disassembly.

A previous owner had been in there and at least replaced the o-ring and rear main seal.  He also went into the sprag clutch as witnessed by a bunch of tool and hammer(?) marks on the parts of the sprag assembly.  When he reassembled everything he left out the shim/washer that goes under the bolt that holds the alternator drive dog onto the sprag clutch shaft.  The play the missing washer allowed caused the bearing that supports the dog to go bad and beat up the inside of the alternator clutch cup eating at least one set of monkey nuts.  It also destroyed the splines on a drive dog last summer.

I also found a sizeable amount of scuffing on the teeth of the intermediate shaft between the starter and the sprag(Possibly a result of the missing washer and it's resulting mechanical mayhem),  specifically, on the teeth that drive the sprag.  Fortunately, I had a spare engine that was able to donate good replacements. 

To reiterate, my engine had a symphony of noise that occurred at idle and just above.  A rough sort of grinding mechanical noise attributable now to the alternator dog bearing and a loud clanking as if hitting an anvil with a hammer.  I attribute that to the play in the balancer shaft.

In all the inspections I did, the one place I didn't find any issue was the anti-backlash gear and spring on the output shaft.  All parts there were perfect and looked virtually new.  This surprised me in that this was where I was sure the source of the clanking was to be found.

Right now I am in the final stages of getting the bearing and seals to finish the engine assembly.  There are a few more jobs like the installation of an electronic cruise control that will take some time before I get her on the road.  As soon as I am able to get the engine running I will be posting back with an update on how the repairs worked out.

For those who wish to always do it right when opening up an engine to fix what may be ailing her, don't you sometimes get aggro at the obvious hamfistedness of those who came before you!?

One more thing:  In researching the engine in the area of the sprag and the starter gear I noticed that the bearing that supports the alternator drive dog is about as far away from the lubricating system as you can get inside the engine and appears to be at the mercy of what ever oil manages to splash or be flung into that area. 

Seems like a pretty tough life for what is listed as a light duty bearing.  When I get the replacement tomorrow I think I'll can get a little heavier duty bearing.  I don't want to go back in there again.

Two Wheels Better wrote:For those who wish to always do it right when opening up an engine to fix what may be ailing her, don't you sometimes get aggro at the obvious hamfistedness of those who came before you!?

Oh yeah don't I what and to make it worse they are often those who call themselves professional.
I refer to them as "Passion fingers"  http://www.urbandictionary.com/define.php?term=passion+fingers

Point-Seven-Five, I’ve been sitting back quite unashamedly, reading with great interest your, and others’, comments on this while I’m waiting interminably for various parts to arrive. You and I have been digging into our respective machines (both K75RT’s) trying to find the source of a seemingly common problem.

We’ve both looked at what we thought was the problem (the anti-backlash spring) and came up with the same observations. Nada! Everything, for the most part, is pristine.
You’ve had some really insightful thoughts and observations on what you feel are some root causes, far beyond what my mechanical mind can come up with, so thanks for all your input on this.

As a matter of interest, for years I’ve been chasing another problem. A vibration at higher rpm’s in the right rear footpeg that drove my wife to distraction. Last year I was able to trace a vibration from there back to the clutch pushrod at the actuating lever point. It was also accompanied by a knock which really puzzled me because I had gone over the clutch assembly the previous year with a fine tooth comb, replacing a number of things I thought could have been the source. Didn’t help in the least.

A week or so ago when I was about to start re-assembling things after the anti-backlash spring disappointment, I cleaned up the main rear bearing on the output shaft and found that it was having a problem. Spinning it while dry I found it had a knock. I think this would have been the source of what I found at the clutch rod end. I’m waiting for a replacement now before getting on with the rebuild and I hope to god at least that problem is resolved.

I also think that having neglected torquing the clutch nut at every spline lube since buying the bike new in ‘91 could have something to do with the horrid clatter in the rpm range that I’m experiencing. At least I hope so! Although I’ve ordered a new shim to replace the original one that sits around the drive gear bearing boss and is showing some wear I’m still uncertain if installing a thicker one which the bearing inner race definitely will sit on is the right thing to do. (Ref. my post on this thread on Feb 16) Given the differences between the K100 and the K75 in this area the info about shim clearance given by Haynes is vague and appears to refer only to the K100 situation. Rene Z’s observations on shims (above) apply to the K100. Should I stick with the original one and just reposition it to account for the wear area on it? At a real loss here as I can’t face digging into the guts of this machine to this extent ever again. Any advice from anyone would be welcome.

Something I was about to ask you Point Seven Five was, now that you’ve gone through much of the re-assembly process and put so much thought to all of this, do you have any explanation for the clattering noise being absent when the bike is run with the alternator removed? Mine did the same but at least you may have found a problem source from your previous owner’s hamfisted repairs. I’m the only one that has ever undertaken repairs on my bike, hamfisted or not, and I have never gone beyond the usual spline lubes.

Sorry for such a long post guys, but as I’m feeling at the limits of my abilities regarding this problem I’m just reaching out and trying to clear my mind’s clutter on the issue. Any further thoughts are most gratefully received.

Thanks ... Malcolm

Malcolm, with respect to the shim, I think that it's purpose is to take up any gap between the inner race of the gear and the circlip that retains it.  It seems like a pain in the ass to size it since one needs to assemble the the bearing on the gear, install the circlip and then take a measurement of the gap between the race and the circlip.  Then the bearing needs to be removed again and the correct shim determined and installed. 

Fortunately on my engine there was no wear so the original shim was ok.  To be honest, I am puzzled as to why you need to reshim if you aren't changing any of the parts in the assembly.  I can't see any reason for relative movement between the shim and the race or the face of the gear that could cause any wear.  Have you assembled the parts and checked for any gap?

As far as the absence of noise with the alternator removed, I am at a loss.  Outside of any side loading on the dog's bearing by the alternator there is nothing that would seem to eliminate the cause of the clank other than the roughness of the bearing being transmitted through the gear rotation to the balancer shaft.  And that seems to be a very remote possibility. 

It's been something like three weeks that I have been looking at this engine and it is beginning to annoy me that I am not done with it yet.  I am getting eager to see if my hypothesis is correct and retorquing the clutch nut with spotlessly clean faces stops the clank and the clean gears and new bearing clear up the rumbly alternator drive.  With the way the rest of the engine is working, I should have the equivalent of a new machine.  I sure hope so because I am looking at a 5000 mile trip with it this summer.

Point-Seven-five wrote:Mike, when you say intermediate gear, do you mean the starter gear?  Do you push start?

Sorry, you'll have to excuse my terminology. 
I meant of course the Idle gear on the output shaft which from the images posted earlier in the thread, I thought that's where Rhodes dash was looking for his mystery noise. While the 75 and the 100/1100 have slightly different output shafts, the effect of a noisy idle gear is the same- I've taken mine out and all is OK and quiet.

Point Seven Five, thought I'd post a couple of pictures to show where I'm coming from regarding the shim.

The first one clearly shows wear on the shim from the inner bearing race resting directly on it.



This photo shows a little wear on the gear facing from the shim. Note that it is unequal and goes only about 65% of the way around.



This photo shows unequal wear on the side of the shim facing the gear. It pretty well matches the wear on the gear face.



Nothing like developing a good neurosis!  The bottom line is that I'm going to just re-install the shim as it was and be done with it, unless of course someone can feed my neurosis with something like 'Have you been adding an appropriate amount of blinker oil?' 

Another couple of weeks to go before parts arrive.