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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: cycle thread on November 26, 2015, 02:51:07 PM
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Hello all.
I have an engine noise on my 1989 K75, its in the lower rev range, from tick-over to, say, 3500 revs?, its a rattle with a bit of knocking, I did think it was the cam chain, but no such luck, have replaced all parts, and still the noise persists.
After listening to the engine again, very carefully and with the help of a long handled screwdriver, to listen through, I am now sure its coming from the rear of the engine.
Pulling in the clutch makes no difference at all.
After reading a previous thread on here, http://www.motobrick.com/index.php/topic,6465.0.html, a light has switched on after reading the post from Kyle10, where he writes about changing the backlash eliminator spring on the output shaft on his K, I guess a K100 as Kyle mentions to replace the rubber dogs.
So I took another look at the Clymer manual, fourth printing 2011, on page 130, oil pan, lower crankcase half and output shaft, it states there was a BMW service information bulletin - October 1988 no 11 037 88 (2289) revision, if there is a distinct noise coming from somewhere between the crankshaft and the output shaft gears, there could be a problem with the springs in the output shaft.
They describe the noise between a whine, rattle and knock, usually in the lower revs.
Not sure if the above applies to both K100 and K75?, I see on the drawing for the K75 output, balance, shaft, Haynes and Clymer, there is a spring between the drive gear and anti backlash gear, also a diaphragm spring (early models)/spring washer on the other side of the anti backlash gear.
Have I found my problem?, has any one had any experience of this?, where to get the parts from in the UK?, any other ideas?.
Sorry for such a long post!, its driving me mad, do not want to ride K75 anymore, until I can sort it out, just in case something might go bang....
Motorcycle also seems to vibrate a bit, well, seems more than I was lead to believe a K75 should do!...
Thanks,
John
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Could be the rubber alternator drive nuts ("monkey nuts"). Remove your alternator and start it up and see how it sounds
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Thanks F14, good advice, I am sure that the trouble is indeed the backlash eliminator spring on the output shaft, but I think it will be a good idea to remove the alternator, an easy test to do, silly not to try something so easy to do,
John
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I too, have that rattle in my 1994 K75RT, and it goes away when I remove the alternator. HOWEVER, two sets of monkey nutz have failed to make it go away.
Some time last year I stumbled upon a 15 second video on You Tube of someone holding a K75 output shaft and twisting the backlash gear back and forth. Lo and Behold! There was the noise my bike makes. It appears the spring that tensions the anti backlash gear is frequently not up to the job, and loses it's ability to load the backlash gear against rattling at low speeds. Why the backlash gear doesn't rattle when the alternator is removed is a mystery.
I have ordered the part and it's replacement is one of the jobs I hope to do this winter if I am feeling very ambitious.
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I'll have to look at mine. Mine has an identical problem. I replaced the "monkey nuts" and no luck. This is at the front of the drive shaft?
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Ignore that. I looked up the diagram. Definitely not in the driveshaft. Anyone know how difficult it is to get to this part? I'm used to wet clutches and chain drive so this is new to me.
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I'm pretty sure to get to that backlash spring, you will have to remove the intermediate housing from the rear of the engine block.
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Yes, you need to remove the intermediate section to check the tension on the backlash gear. You will need to remove the oil pan, and I think the hall effect sensors to pull the output shaft so you are able to remove the anti-backlash gear to get to the spring.
Probably not a bad time to give the sprag a good cleaning as well. I also want to check the alternator drive on mine to see what stripped out the splines on the alternator dog last summer.
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Here is a link to an interesting site Darthbane 71, kindly passed onto me by Kyle10, about half way down the page, a shows the offending spring really well, and gives a good visual reference to how it all goes together, http://hrsbstaff.ednet.ns.ca/bvogel/K100/K100.htm, you are quite right Scott, spot on Mighty Gryphon.
Simple enough once the engine is separated from the frame and gearbox, and as far as I can see, no need to disturb either the crankshaft or the top end!, which will save a lot of work.
Very interesting about how the noise seems to stop when you remove the alternator Mighty Gryphon, as the noise on my K75 does seem quite loud when I hold a long bladed screwdriver, like a stethoscope, to the alternator body, I am wondering if the alloy body is acting like an amplifier?, as the noise itself certainly seems to originate from a bit lower down, as in the balance/output shaft, I have not yet tried running the engine with the alternator removed, but will do so, will be interesting to see if it makes a difference.
I am a little worried that the rattle might be causing damage, perhaps through extra vibration, or the gears themselves, so have decided not to ride my K75 until I have cured the problem, a bit overcautious maybe?...
John
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I’ve read this thread with a lot of interest, having just come across it, as I have the same rattle/clunk in my ‘91 K75RT. It appears during gradual acceleration in all gears between 3500 and 3700 rpm. I’ve been dealing with this for well over a year now and have put on a few thousand kilometres with no noticeable change in the problem, except for my enthusiasm for riding the bike having diminished.
Last summer I did the monkey nuts change and replaced the bearings in the alternator, neither of which made any difference. Finally I tried running the bike without the alternator, and, yep, the noise was gone. My (hopeful) conclusion was that it was the bearing in the auxiliary alternator drive that, without the load put on it with the alternator attached, caused the noise to disappear. The other option which I gleaned from another discussion forum was the wear on the anti backlash spring. (Cycle thread, that’s the forum you provided the link to in your last posting)
A couple of weeks ago I removed the intermediate housing and found that the bearing in the auxiliary alternator drive was in pristine condition. I’ve since been waffling about trying to decide if it really is the anti backlash spring, which involves removing the engine - a pretty daunting task for me. Or could it be something I’ve missed in my work so far.
I’ve since come across this thread in this forum and what really grabbed my attention were all the parallels to my situation and the comments about the anti backlash spring and the disappearing of the noise relating to the alternator removal.
All my procrastination and waffling have now been over-ridden and I’ve definitely decided to take the plunge, remove the engine, and replace the anti backlash spring. I hope to start on this in the next several days.
‘Mighty Griffon’ and ‘cycle thread’, just curious, have either of you gone ahead with this and, if so, what were your results?
Regards .... Malcolm
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What would be helpful would be for you to post an mp3 recording of the sound before you do the work.
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You're right Laitch. It would have been be a good thing to do, but it's Canada, it's January, there's snow outside, and the bike is in the basement stripped of everything up to, and including, the intermediate housing. Worst of all I'm one of those dinosaurs (perhaps 'Old Fossils' is more appropriate) that doesn't have the where-with-all or the equipment to make an mp3 recording, let alone post it here. Please don't think I'm being facetious, because it really would have been a good thing to have done to perhaps clarify a vague situation to the more trained ears amongst us. Something for others to consider in order to help resolve other problems in the future. Thanks for the suggestion.
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I don't have mine disassembled so I can't confirm its not the alternator, but I replaced the "monkey nuts" and am having the exact same problem. I'll see if I can post a video/audio clip here in the next few days.
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That would be great if you could. I tried replicating the sound with the bike on the centre stand, in the problem rpm's, and dragging the rear brake to mimic things being under load, but with no success. I would think an on-the-road recording could be tough, but then I'm one of those Old Fossils. :dunno2:
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Ive had similar problems with replicating the noise while not moving but I'll give it a try
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I haven't gotten into my 75RT as of yet. I'm still in the process of reassembling the engine on my 100RS. With the warm weather, I hope to get that done this weekend. Then it will be the RT's turn for work. Since I am now into mid January and I can't work in the garage if it is colder than 25 degrees F outside, I anticipate it being a rather long job spending a lot of time waiting for the temperature to get to 30F or above.
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My '75 is now in pieces waiting for the final surgery to replace the anti-backlash spring. I haven't removed the lower crankshaft half yet in order to access the output shaft as I'm waiting for partsbecauses I want to have them on-hand for the'big day'. Haynes says there's a tool (BMW 12 4 600) that's required to refit the anti-backlash gear. Anyone who's done this job fabricated one, or have you managed to do the job without it? Have a few weeks to wait before parts arrive.
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Watching this thread as well...approx 71k miles on engine...DEFINITELY right upper rear of engine in the "alternator area"...
All TB rubbers replaced, TB Synch, air leak checks, breather hose replaced, coils, wires and plugs renewed, Monkey nutz, drive cups (these looked great but due to age I replaced) and alternator bearings replaced removal of alternator all yield no-joy...same 'rattle' when I blip the throttle off idle - with or without the alternator installed....when riding noise immediately goes away ~2500 rpm and up, not to return until pulling away from a stop...."sounds like" gears walking on shaft to me....
Any further progress? If you completed the job, did you need that BMW Special tool for the anti backlash spring install?
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Mine has same noise. Resigned to pulling the engine later this year to fix. Sigh. Only about 30k miles on engine.
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Mine has same noise. Resigned to pulling the engine later this year to fix. Sigh. Only about 30k miles on engine.
Could you please post a sound file of that noise, Marshall?
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Well, my first youtube attempt ever, hope it posts up ok....my sound occurs as the throttle is blipped off idle and when pulling away from stops....again, makes no difference with alternator on or off, clutch in or out....
https://www.youtube.com/watch?v=HfDR3tkR8C0 (https://www.youtube.com/watch?v=HfDR3tkR8C0)
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Well, my first youtube attempt ever, hope it posts up ok.
Good work! Is this noise a recent occurrence or has it been developing volume?
Regardless, it sounds a little like mine always has—currently at 51K from ~20K when I bought it—if I blip the throttle or under-rev, so I'm neither a blipper nor lugger; however, blipping the throttle should have better effect as a mating call and be less hard on the bike than White Dog's technique. He simply drops the whole bike and even doing that doesn't get him attention.
I just can't be concerned with that sound, gawd hep me. I start off and proceed from gear to gear with plenty of revs. I don't hear it unless I allow the engine to lug, but doing that is unnecessary.
I'll need a lot more encouragement—maybe even cash payments—to get me started worrying about it right now. If at 70K my bike sounds like yours, only incoming cash will change my outlook.
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I can't really tell from the sound of your video on my crap laptop speakettes, but if it is a bit of a clank from the back end of the engine that happens between about 1100 and 2000rpm it may be the balance shaft beinga tiny bit loose.
In the K75 the balance shaft is linked to the output gears with a slot and tab arrangement. The guys a BMW for some reason decided that there should be about 1/16" play between the tab and the slot. What you hear is the tab banging around in the slot. The picture below shows the slot and the shitty fit on my engine.
The problem seems to be that over time the shaft stretches slightly and the friction between the balance shaft and the output gear is reduced to where the shaft is free to move. The fix is fairly easy once the transmission and the clutch are pulled off which makes it a good job to do with a spline lube and o ring replacement.
The fix is to remove the clutch basket and degrease the face of the balance shaft which is inside the engine. This can be done by shooting some brake cleaner into the center of the output gears onto the face of the balance shaft. Degrease the mating face of the clutch hub and reassemble making sure to torque the clutch nut to the top end of it's torque specification. This is what I did to mine and it eliminated the clank.
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I purchased my 94 K75RT 2 years ago with ~68k on the clock. and zero service history....the dis-assembly began and in hindsight, I didn't go far enough.
I'm listing work done to maybe help others to 'cross stuff off their list' of possible causes to this noise. My apologies if long winded, but, if it helps......
Replaced:
What started 'all of this' was heavy weepage of oil out of trans inspection hole. Dis-assembly discovered bad trans drive shaft splines with a trans oil seal failure at said trans drive shaft. Replaced with good condition 30k mile trans from a K100rs. Had to replace clutch disk, (OEM), with main seal and clutch pack bolts...drive & driven plates looked in great shape - no bluing or warpage, thickness good, new disk was a good fit on splines of tranny drive shaft and I got the balance marks right on re-assembly. Replaced all the trans seals, etc., and inspected the gears, shafts, bearings inside, everything go. Of course full spline lubrication to all joints required.
Having ridden the bike only ~100 miles or so after purchase, I cannot remember if this "noise" was present with the orig trans or not, which is driving me crazy not knowing. But clutch in or out, the noise still emanates from slightly forward and 'down' of the alt area by listening with stethoscope.
Replaced Monkey nutz, drive cups, alternator bearings - just because... the originals looked new, frankly.
Dis-assembled and cleaned starter. Nothing looked out of the ordinary, but again, I wasn't hunting for this sound back then.
Cleaned TB's and injectors w/new o rings, inspected 'very clean' air filter, replaced bushings and manifolds and clamps, fuel filter, all fuel lines and after adjusting valves, replacing plugs, inspecting coils/wires,, gave it a proper synch using manometer. (The original plugs looked uniform and that light brown color that I expected...nothing abnormal.)
Engine runs like a champ, idles like it should, but there's that 'rattle' at throttle blip and take off..it's not coming from the front of the engine, so timing chain/tensioner is ruled out...
Maybe the problem lies with slop in the starter idler gear arrangement which means the intermediate housing comes off. AND, if I go THAT far, do I just drop the engine and check for this anti-backlash spring issue? I see in the fische that there is indeed a circlip looking spring on the K75 engine output shaft (11 21 1 460 70 SPRING)....anybody had experience here?
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Sooooo, Gryph, the intermediate housing does NOT have to be removed for this? I apologize for being a bit numbskull, but I can't help but focus on whats 'behind' that housing...if its just the trans and clutch pack...I'd be relieved!!
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When I first bought my 1100 I noticed a knock just like that. Took it to the dealer who had a great service manager back then. He said, after listening to it, "sounds like a good strong K bike." That was 50 thousand plus miles ago. Just saying.
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Here is mine
https://youtu.be/q-3Ewx5VkYM
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Gryphon's right. I went through the huge effort this winter tracking 'the noise'. I was convinced it was the anti-backlash gear assy. Took the engine out of the bike ('91 K75RT), opened up its guts and found nothing wrong in there. It appears that torquing the retaining nut on the output shaft/clutch housing does the trick as 'the noise' is gone now. Could have saved myself a HUGE amount of time and effort by doing the torquing along with a spine lube. You can check out a long thread on this subject on the K100 forum. Look for the thread 'engine clatter'. (I hope I haven't breached protocol by making this reference)
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Mlytle, that's the exact same sound mine makes, but mine is 'slightly' quieter.....Rhodes, I will take yours and Gryph's advice to clean mating surfaces and re-torque the clutch to output shaft nut to the higher factory spec.
I'll relax, Mystic !!! Sounds like these are psychological mind humpty-humps..... I'm going to get after this this winter and report back then...thanks all...
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My simian buddy, I am willing to bet that when you di your clutch work you got a bit of oil on the interface between the clutch hub and the balancer shaft. I suspect that is all it takes to let them move and bang around. Any clutch work including an o ring replacement will break the connection between the shaft and the clutch hub and open the door for the motion and the clank.
I have a photo of the parts where the clank comes from. I was able to make the noise with them on my bench when the engine was apart. I can't post them for a couple days because they are on a different computer.
It should be an easy fix, you don't even have to take the engine out of the frame.
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Gryph....I've just had that 'Ah-Hah' moment......being careful about the clutch hub torque, i gave zero thought to oil fouling of the interface to the balance shaft...as i....wait for it.....oiled up everything there as to not oil starve the bearing/seal relationship until engine oil pressure took over............*takes palm of hand - smacks forehead*.....but then again, without this forum, how would one know about this little delightful delicacy ??? Thank you for your insight. I know exactly what to do now......
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You know, Johnny, I've listened to every last you tube vid I could find of folks revving their bikes off idle and could not come to the same conclusion you have, as I just could not hear it...so my feeble mind wandered to this being a specific issue....and of course due to my 'complete waste of time' research tactics, the end result is just ride the thing.
That being said, I now realize that I just need to whack the throttle, as you so eloquently say....thanks
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the only motobricks i have heard that did not sound like that were the one not running...
I have another k75 with same mileage as mine in my shop. Whisper smooth. Zero knock or rattling.
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I have another k75 with same mileage as mine in my shop. Whisper smooth. Zero knock or rattling.
How many miles and which year, Marshall?
I'm in agreement with j o and mystic red, I think. I do understand though, the quest for perfection. My good fortune is that I've accepted it's out of my grasp regardless of how convenient it is for others to access.
With that in mind, what seems to be the topic here is that hollow, low-pitched, rattle occurring during a slow transition from idle to slightly higher revs. My bike did that when I first got it but I haven't let it do that since I got a message from the mothership via my dentition that said, "more revs, more revs." Timing increased revs with the release of the clutch damps that noise regardless of its origin. It just isn't there when I shift with enough revs—that doesn't necessarily mean whacking the throttle—as fun as that is. It just means more revs quicker.
If there is another sound that is being discussed other than that one, thankfully, I can't hear it.
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Thanks for the audio, Marshall.
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93/94 years. 35k miles.
Had to moto around at 5-10mph in first gear a bit last weekend. Rattle was very annoying and un-bmw like.
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Rattle was very annoying and un-bmw like.
That I can understand, Marshall, especially because you've been involved with race tuning BMW engines and are accustomed, probably, to getting submission from them. Poking along on my K is my least favorite sport. I don't allow it to rattle though. I'm in the clutch friction zone and on the back brake, revving, and slipping along. The only thing that makes it interesting is testing how long I can balance at a standstill.
Mine will quietly behave at low speed but whenever I can briefly accelerate I slip the clutch to raise the revs. Mostly, I avoid city traffic, parades and funeral corteges when on the K.
That whisper-quiet K is one I'd like to meet but I'm satisfied with the one I've got.
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Neither of my K75's clank anymore. The Yellow one never did, but it only has 36k miles. The Red one has 71K miles and has did it as long as I've owned it which is since 55k miles. The Red one clanked a lot at idle which made it sound like a piece of shit when I was sitting at lights or when starting the engine before riding out.
Why the F should I burn up my clutch in traffic to stop the clank? Slipping the clutch while I wait for the tan Buick in front of me to accelerate enough to let me get above 2000 rpm in 1st isn't my idea of good engine management. I used that brick for commuting and as a result got stuck in stop and go quite often.
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Why the F should I burn up my clutch in traffic to stop the clank?
You shouldn't burn up your clutch, Gryph. It smells bad when you do that.
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So I'm going to tear into this in about a week...I've ordered up the requisite o ring, nut and 'compression ring' and my question to you all is:
Whilst I have this apart, anything you'd like pics of, (no wait, that sounded just wrong) or check and then relay back anything else in there for your own piece of mind if you're considering doing this?
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So I'm going to tear into this in about a week...I've ordered up the requisite o ring, nut and 'compression ring' and my question to you all is:
Whilst I have this apart, anything you'd like pics of, (no wait, that sounded just wrong) or check and then relay back anything else in there for your own piece of mind if you're considering doing this?
You could start a thread in the Projects section and photograph the job in its stages with a description of what you encounter and how you tackle things. If you run across any foreign currency, critters or unidentified objects in there, post photos of those, too.
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Kicked that idea around. but one would think taking the clutch off has kinda been played through posts - here and elsewhere, right? My thoughts were if someone dealing with this specific issue had curiosities... I dunno....
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hey G_A,
It would be interesting and helpful to know if you can manually cause the sound to occur using a lever or bar or wrench to rotate the shaft back and forth at the earliest stage before you get all the way to pulling the bottom. Like can you make the sound by rocking with the pressure plate attached, or after the clutch is removed and rocking the output shaft at the flange, etc. Just as a diagnostic method to indicate that the anti-backlash spring is the culprit before doing the full-blown disassembly. thanks, kb
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It would be interesting and helpful to know if you can manually cause the sound to occur using a lever or bar or wrench to rotate the shaft back and forth at the earliest stage before you get all the way to pulling the bottom. Like can you make the sound by rocking with the pressure plate attached, or after the clutch is removed and rocking the output shaft at the flange, etc.
Kind of like this, kennybobby? This may be the video Gryph mentioned earlier.
Knock check (https://www.youtube.com/watch?v=gMgB3FI47IA)
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That's a clack right there..... But according to what Gryph and Rhoads were saying, this isn't transmission related.....(YMMV).
KB, you bring up a good idea...once the tranny's pulled, I'll attempt to see if the sound can be replicated by manual manipulation...I gather I'm looking for some kind of end float scenario at the flywheel....
I'll report back with my findings (if any). And IF I do find a culprit audibly, then Laitch, I think your idea of a new thread post would be in order.
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Same noise I had, but mine was found to be from the dogs on the balance shaft hitting the sides of the slots in the output gear. Because of the balance shaft on the K75 it is unique to that engine and not a problem on the K100's.
I would expect the clacking in the video to stop when the clutch is pulled in and the transmission is in gear. On my bike the clacking was there all the time whether the transmission was in gear or not or whether the clutch was in or out.
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Exploratory tear down begins: As of right now I'm down to flywheel removal...and nothing out of the ordinary has raised it's head.
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All the transmission fasteners including the clutch pack allen screws were tight......
I sheephishly attempted to show in pics - one handed because of the phone cam - gently pushing, pulling, twisting, torqueing the clutch assy to see if I could reproduce "The Knock"...I could spin the engine a little both directions, but no end float, no tangs in tab slap, nothing............so, off with the flywheel...but the Texas heat is preventing me from working in the garage today (yesterday, tomorrow etc)
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What I think Gryphon and Rhoades were trying to explain is diagrammed here.... the Output Shaft has "slots" which are engaged by the "tabs" on the Gear Wheel shown here which is inside the engine cases behind the flywheel. ...and by removing the flywheel, cleaning (by contact cleaner)
through the holes of the 'Gear Wheel' - reaching the slots in the output shaft - and then reinstalling the flywheel (with new nut, compression ring and o ring of course) and torquing the nut to the largest of the recommended BMW spec for the nut, the problem should be solved.....TBC....
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Item #8 in the diagram is the anti-backlash spring, a source of noise in the K100's. The notch looks like a good candidate also.
The balance shaft is accessible thru the bottom of the brick, the oil sump area, which if you remove the cover may let you hear the clank better.
For sure the noise is not caused by dirt--that's the cleanest bike, clutch and workshop i've ever seen...
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You're creating a useful pictorial essay, gone_ape.
Looking forward to hearing a YouTube presentation of your throttle blipping after the procedure, which would seem to indicate a stark lack excitement in my life right now that I had better correct.
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Thanks Ape! Your illustrations are perfect! Now even I understand what I was trying to explain.
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Thank you Laitch and KennyB... You've heard of a "20 yard car" (looks great from 20 yds away), same with my garage !!! Cans of brake cleaner go a long way to getting that look....Laitch, your posts almost always bring the chuckling guffaw!!!
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Got a little further.....and still don't have much of a conclusion...so:
Pushing/pulling/twisting the clutch hub (sans clutch pack) revealed nothing 'abnormal'... I stuck a pick in between the Gear Wheels to see if I could get anything to move..solid, no movement... So I took Gryphon's advice to clean the output shaft to gear wheel mating surface and reinstall the trans back in the bike.....
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I made a another stupid vid showing the output shaft's "play" withe the clutch hub removed.. First time I took the hub off I was a little alarmed at the play in that shaft..A lot of searching on these here forums finally revealed this to be a normal event as per factory manual on page 11-38 state's as follows:
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I think you would have better results cleaning the face of the balance shaft if the spoosh tube on the cleaner was straight.
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So that a continuance of Laitch's stark lack of excitement remains at the forefront, I dedicate this vid to him ....
https://youtu.be/I3Z9jJ_x9fE
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I actually did both.....I had 2 cans of the cleaner, one bent tube the other straight. I experienced epic fail by not taking pics of both...let the flogging begin.........
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i think you may have found the source of the knocking sound--that just seems too loose like the driveshaft notches that hold the gear tabs are worn out.
i read that note as a loose sliding fit of the bearings on the shaft, instead of a tight press fit--meaning that you don't need a bearing puller to remove the bearing and gear, they will just slide off (or fall off the end and hit your foot if you don't pay attention).
But even with a sliding fit of a bearing on a shaft there should not be that much radial motion...?
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KB.... Interesting, very interesting. One of the things I tried to observe was the 'sliding fit' of the clutch hub to gear wheel combo....completely rudimentary and done only by hand and by rocking and twisting the hub with the nut off. There really wasn't much discernible play let alone slop in that assy. Perhaps a 'little' is all it takes and as Gryphon mentioned earlier, his experience was down to thickness of oil film and possible stretch in the balance shaft materials....
I'm no engineer, just a pea brain, but the audible tone of rattling that output shaft around in the video was pretty close in 'clack' frequency to what I think I'm hearing when the engine is running.
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My next question to you all:
Only those with a K75, please as the the K100 has a different arrangement....When you've had your clutch hub off - how much slop or play did the balance shaft have??
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My next question to you all:
Only those with a K75, please as the the K100 has a different arrangement....When you've had your clutch hub off - how much slop or play did the balance shaft have??
My bike can have the same noise as yours, gone_ape. When I performed input shaft lube service, the amount of play didn't register—not surprising given my current graceful decline—but after reassembly with the correct torque values, there's no discernible difference in the amount of rattle it has been producing in the last 35K miles. The engine will produce it if it's lugged or moving off the line at very low revs in first gear.
Gryph seems to have gotten positive results though with his cleaning-torquing technique. If I outlive this clutch disk, I'll pay closer attention when I—or my nursing assistant—replace it.
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When the clutch hub is inserted into the output shaft spline, then the radial motion of the hub is constrained by the oil seal and the large bearing on the balancer shaft that is clamped by the engine cases (main crankcase casting and the lower section).
Sorry i don't have an open clutch sitting around to go check that shaft play. But it's hard to believe that much radial motion is within spec. Maybe the roller bearings in the gear are worn out.
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As it's not splined, it seems the output shaft is only supported when the clutch hub via the splined gear wheel assy is torqued together, right?
So KB, I think you're on to something.... the gear wheel 'tabs' and the output shaft 'slots' (with which they engage each other) have somehow worn and have developed this 'slop' ........makes sense.
Well, I guess I'll ride it till a tab breaks off, because I can't find anything on any forum that discusses this issue....uh, maybe cuz it's "not" an issue, right?
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Laitch, the clutch pack and clutch hub had to be removed completely to register this 'slop'....I couldn't replicate with any of the clutch pieces installed.
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10-4
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I think I found where my confusion started. Digging around the K100 forum, a forum member was attempting to get at then repair his k75 rear main seal. His comments I edited just to get to the good stuff....and unfortunately, just got the one reply back, adding more drama to my plight....
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just got the one reply back, adding more drama to my plight....
Plight? Drama? You were doing ok on your own with those. Some of us are waiting patiently for the new throttle blip. Have some compassion and move forward, please.
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Ape, the slop in the tang to slot fit appears to me to have been designed in. When I had my engine apart last winter I examined those parts quite closely and could find no evidence of any wear that may have contributed to the sloppy fit and the resulting play.
If indeed the play is a design feature, I have no idea what it is supposed to do. The only idea I can come up with is that the slight amount of play there would allow the balance shaft to adjust itself slightly to more accurately dynamically balance the engine.
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Thanks for sharing your notes and pictures of this investigation.
Here's my guess about why it's such a loose fit--to ease assembly of the clutch hub.
If the radial position of the balancer shaft was designed to be held and fixed exactly concentric with the gear splines and the gear hub bearing, then it would over-constrain the fitting of the clutch hub--it would have to match perfectly at both the inner diameter and the outer splined diameter and could be difficult to assemble. Instead it is only constained by the hub bearing for assembly and snugged up into final position by the nut.
The more important constraint or fit is the crank gear to the output gear, the tabbed drive of the balancer shaft doesn't require as much precision--the balancer floats axially on the front roller bearing.
Now what is making the noise and why does it sometimes go away when the alternator load is removed, or after re-torquing the nut?
It is due to a slight relative motion between the drive gear and the driven gears allowed by the anti-backlash spring, and the position of the tab and slot during final torque of the nut.
The output gear has an anti-backlash spring to keep and maintain gear face contact, but the gear for the alternator does not. Both the output and the alternator have different torque loads on the main crank gear that varies during one revolution. In addition the output gear is coupled to the balancer shaft thru the clutch hub nut torque and the final position of the slot and tab.
If the tab is very close to, or barely touching, the edge of the slot during the tightening of the clutch nut then the action of the anti-backlash spring combined with the load of the balancer weights and the alternator torque will allow the tab and slot edge to move and hit and clank against each other.
Once the nut is tight the position of the gear tab/slot is fixed. If the nut is loosened and re-torqued then the position or gap between the tab and slot edge may move slightly to increase the gap such that no contact can occur during the fluctuating torque loads, (or it forces the gap closed so tightly that it can not open?) Those lucky folks have the quiet bikes. Any relative motion occurs within the gap of the tab and slot and so no contact is made and no sound occurs.
When the alternator is removed it has possibly changed or reduced the peak torque load in such a way that the relative motion is lesser and no clanking occurs. The anti-backlash spring is sufficient to hold everything in a quiet position without the reflected torque load of the alternator thru the crank gear.
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Holy Crap, KennyBobby !!! You earned your P.H.D. with this epic dissertation...fantastic breakdown-a-bility in those paragraphs....i can now sleep at night knowing my 'noise' isn't fatal because of this deep conversation. I can only hope I have not wasted anybody's time.
That said, Laitch, your video will not be forthcoming this weekend. The transmission was fiddly returning to it's post and me grunting and groaning caused this......parts have been ordered....
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That damn POS boot has to be the source of most of BMW's profit. $40 every time you even think about touching the back side of the transmission. Grrr...
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Yeah, undo the clamp before "you even think about touching the back side of the transmission".
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And my local dealer stocks EXACTLY nothing.. Not even for newer machines...sad.... Viva la multi-brand dealerships...so I mail order everything these days..
Well, being a half wit, I at least drained the trans fluid prior to all this...if I was a 'no wit' I'd be left with a puddle.....so once again I find out 'after the fact' what to do...
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I always wire up the actuator arm to the transmission case when I remove the clutch cable. It remains wired up even if removing the transmission for servicing. I've never torn a boot using this technique (thanks goes to Bert at K100-forum).
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Also makes for an opertune time to remove the arm and clean/lubricate the little baby roller bearings down in there.....
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Just an update...got it all back together.....and.....as Led Zeppelin so notably proclaimed....The Song Remains the Same.....nothing changed...ALL THAT and there was zee-ro change in the bikes countenance of sound..Sorry Laitch, "No Movie Tonight"...I gave it the business and whatever this noise continues to be, I'm going to have to crack open the engine to really see......or not.
If it breaks, fine....it may never break and that's fine too. I tried and came up snake eyes...but I did have fun, and isn't that what it's all about?
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That's how my '87 K75 sounds, for the 50k km I have driven it. I thought it was meant to sound like that. Perhaps I am missing something. Old ears.
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Disappointed to hear that you weren't able to cure the noise in your engine. As far as mine, I am able to report that after putting over 6000 miles on her in the past 2 weeks including a 24 hour flogging at 75+ the clank I had is still gone and the engine runs smoother than ever.
There is a very slight knock that occasionally occurs at cruising speed(70+) when the engine is hot and the bike has beeen running for a couple of hours, but it comes and goes and doesn't have any effect on the operation of the engine. I am suspecting the bearing for the alternator drive. It was a bit questionable when I had the engine apart last winter, but didn't seem to be bad enough to warrant the cost of replacement. I am beginning to think that with the speeds these engines run at, every bearing has to be perfect to keep things sounding nice and quiet.
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Hi, gone_ape.
Output shaft endfloat is another check to make next time you do a spline lube. Probably need a dial gauge though. If the thinnest blade of a feeler gauge fits between the circlip and bearing, with outward pressure on the shaft, that's a problem, there should be no gap.
Hi K1300S,
That's a good video you posted. Next spline lube, if the circlip end gap is bigger, or less engaged, on your noisy brick than the other, that might be another hint as to the cause of the knock, due to a fatigued circlip.
The circlip is cupped, so also acts as a diaphragm spring, to bind the gear hub to the bearing. These parts are about 30 years old now, so not surprising if it loses a bit of tension.
The K75 has minimal resistance to endfloat, compared with the K100.
Unlike the k100, the power flow through the k75 does not go through the output shaft, so it's main job, other than doubling as a balance shaft, is to drive the pump. Since the output shaft isn't splined, that might be the reason the clutch nut torque is higher on the K75 than the K100. In ft/lb the torque is:
K75 ~100,
K100 ~75
That makes it easy to remember.
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Unlike the k100, the power flow through the k75 does not go through the output shaft, so it's main job, other than doubling as a balance shaft, is to drive the pump. Since the output shaft isn't splined, that might be the reason the clutch nut torque is higher on the K75 than the
Power is transferred to the output shaft of the K75 by the same means as the K100 uses. The main job of the K75's output shaft is the same as that of the K100's output shaft—the transfer of power from the engine to the transmission. See red arrows in the attached diagrams indicating power engagement. The significant differences between the two shafts are the balance weights of the K75's output shaft (green arrows in the diagram, the rearward weight having notches that engage with pins on the gear wheel), and the damper assembly of the K100 output shaft (blue arrow). Both output shafts engage with their respective clutch housing shafts by using splines—splines in the bore of the K75's gear wheel that engage with external splines on its clutch housing shaft; the splines on the output shaft of the K100 that engage with internal splines in the bore of its clutch housing shaft.
Another difference in fastener torque value is that the K100's value is developed by two steps: tighten to ~103 ft.lb., loosen, then tighten to ~73 ft.lb.; the K75's is developed by one step—tighten to ~103 ft.lb..
K75 output shaft.
(http://www.motobrick.com/gallery/3/1601-111120100233.png)
K100 output shaft
(http://www.motobrick.com/gallery/3/1601-111120102311.png)
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To me it's looking like the power flow goes straight from the gear to the clutch basket. Anyway spose I've crammed too much in there cause the point I'm wanting to make is that anyone who has a knocking sound could check for output shaft end float. It would be a simple check when doing a spline lube. If there is any end float at all, that could result in knocking.
Need a dial gauge though.
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To me it's looking like the power flow goes straight from the gear to the clutch basket.
Power is transmitted from the crankshaft gear to the output shaft gear then into the clutch housing via its shaft; it's the same in both models. That's why those are called output shafts. Because the original post and subsequent posts are over three years old—except yours and mine—it's probably all over but the shouting. :laughing4-giggles:
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The sneaky little K75 has splines from the gear to the clutch hub. The K75 output shaft has no splines.
I'll say it's a non urgent fix, and that gone_ape is one of many who have just got used to it, probably still going now just the same.
Have you ever met a man who had a motorcycle with an output shaft that had no splines?
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Have you ever met a man who had a motorcycle with an output shaft that had no splines?
That would be you, daveson, virtually. :laughing1:
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Have a look, yes you have no radials and no splines.
Well except for the name's, and a few other changes,
When you talk about me,
The story's the same one.
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Your story is the same one, yep,
No radials, no splines.
But you don't need a dial gauge
To read between the lines
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Good one, you could make a song out of that.
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A few more thought bubbles. The clutch nut might lose some of its ability as a lock nut, again considering it's age.
If the rattle is worse on acceleration, maybe that's to do with the straight cut gears in the intermediate housing, like on the auxiliary shaft, or the idler spring.
Also you want to be confident about the clutch balance marks, there was a recent case with an unbalance that produced noise more so than vibration (OK its a long shot but an easy check)
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Hi All
Long time between drinks on this topic.
I have a 1992 K75RT with 70,000km on the clock and am experiencing this knocking noise only between 3,500 and 3,700rpm. I thought the motor was going to hand grenade itself when I first heard it. You can accelerate to redline and won’t hear it, only sitting at the nominated revs in any gear.
I have the alternator out at the moment as many have said check the monkey nuts. The appear fine and if I didn’t know better would say they have been previously replaced.
The bike was purchased as a non running project and is now NSW Club registered. I have read many previous ideas relating to this noise (which sounds like a bucket of bolts) and many have stated removing the alternator stops the noise.
I may try this and if the noise disappears, consider spacing back the alternator to reduce any preload on the alternator shaft.
Not keen to pull the box yet 😩😵💫
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I had posted a photo on this back in 2016, but it seems to have disappeared. Here it is again to show what the problem was on my bike. It appears that the power pulses are uneven enough at some rpm to cause acceleration/deceleration of the output shaft to be bad enough to make the tabs rattle in the slots.
[ Invalid Attachment ]
Tightening the clutch nut cured the problem for a year or so, but the noise came back. I think that if I go back in there again, I'll put a bit of Loctite bearing lock on the face of the clutch hub to see if that will keep things together for a longer time. In the meantime, I have found that getting the valve clearances as close to the same as possible and balancing the throttle bodies helps a little.
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Thanks, The Mighty Gryphon.
I had read all the previous threads and was curious if there had been any further development in the field or with owners.
I have also backed off the threaded bolt clutch adjustment underneath the bike, this in turn has changed the tone of the backlash noise when rocking the wheel back and forth in gear.
Clutch operation appears ok in the garage.
Too much rain in Sydney at the moment for a decent test ride.
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Since you have the alternator removed, has the noise now disappeared? If yes, it might also be the alternator itself, does it spin perfectly?
Can you post a video of the backlash noise, and the noise at 3,600rpm?
At 3,600rpm, with the clutch pulled in, does the noise disappear, change, or remain the same?
I spose not, but do you hear a loud, distinct clunk after the engine stops?
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I have also backed off the threaded bolt clutch adjustment underneath the bike, this in turn has changed the tone of the backlash noise when rocking the wheel back and forth in gear.
Usually backing off that bolt on a properly adjusted clutch will interfere with smooth shifting sooner than later. Your field trial could be informative. Are you certain that rattle isn't coming from the timing chain? There's an article at IBMWR (https://ibmwr.org/index.php/2001/11/01/timing-chain-rattle-diagnosis/) written by a Brick owner that chased, caught and defeated a rattle that had been a bother for 10 years. He might have won the coconut for Persistence.
Thanks to many videos and posts from Brick owners over the years, I've learned which rattles are benign—most of them. I've accepted my Brick's occasional imitation of a TR3 because it's more comfortable than a TR3. :laughing4-giggles:
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True. Before we assume the worst, can you pinpoint the exact location of the noise, and does another pair of ears agree? I'll guess the noise with the engine off is unrelated and not very important.
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Hi All
Thanks to all for your comments and input
After reading many threads on this subject and my own riding and mechanical experience, in this particular instance I feel The Mighty Gryphon is on the money.
When I initially discovered this noise it sounded to me to be coming from the top of the motor. It was difficult to diagnose as with the RT Fairing the noise tends to amplify around. If I was a betting man I would have initially said timing chain, however, with different throttle inputs the noise was too inconsistent. You could accelerate briskly towards redline and no noise was evident which to me ruled out timing chain. If you kept the revs between 3,500rpm and 3,700rpm it sounded like a bucket of bolts whilst maintaining a light throttle load. If you backed off or floated the throttle (no load or over run) the noise would stop.
I agree with the theory the noise is a power pulse or harmonic produced by the motor on a light throttle in the nominated rev range. I also agree that the noise is probably generated from the balance shaft tab area. Trying to rectify the amplified noise being generated is the issue.
I have had my alternator out and the monkey nuts appear to be in a very good condition, spinning or turning the alternator by hand is as smooth as silk, there are no tight spots or noise evident.
As some members have previously mentioned their noise was no longer evident with the alternator removed, so I focussed my attention that the alternator when fitted must be pre loading the the drive shaft and contributing to the noise generation. I then glued three flat washers, one on each alternator inside mounting point to release some preload off the alternator drive shaft when the alternator is fitted.
As previously mentioned I have backed off the clutch adjustment bolt underneath to the point where it just touches, This resulted in the arm striking the muffler. Today I carefully reshaped the top of the muffler allowing clearance for the clutch arm. I then adjusted the free play at the lever.
On a short road test today, I would say at least 75 percent of the noise is gone. When I arrived home I removed the alternator and placed an additional washer on the inside mounting points, this equates to a two millimetre thickness spacing which in turn I hope will remove any preload on the alternator drive shaft and hopefully not cause any abnormal or premature wear on the monkey nuts.
Reassembly and test ride tomorrow, fingers crossed 🤞👍🍻
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???
Any updates.
If you're interested in a little experiment, here's one. After removing the crank cover, you might have two small windows of access to the area where the tabs are (at least the k100 pictured does) Clean it, let it dry, paint it, let it dry, a small circle of paint between the tab and the slot. If you still have the noise problem and the paint hasn't cracked, the tabs haven't moved. Or maybe better a dab of paint in the gap.
Or someone else with the problem might want to run the test. Hmm. Maybe.
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Hi All
Apologies for the delay in reply, probably fallen into depression.
Took the bike for a long ride to get it nice and warm, unfortunately the noise is still evident, slightly reduced but evident.
Im just disappointed, such a great bike and a minor mechanical glitch makes it so frustrating.
I will probably just ride it as is at the moment, I do have the time but certainly not the patience to remove the gearbox and replace/torque the clutch nut as has been mentioned previously.
Cheers
Auldy
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Gryph seems to have gotten positive results though with his cleaning-torquing technique. If I outlive this clutch disk, I'll pay closer attention when I—or my nursing assistant—replace it.
As luck would have it, I did outlive the clutch disk because it became oil soaked from running with a leaking engine output shaft o-ring for ≈10,000 miles. Not only did I replace the clutch disk, I also installed new clutch pack screws, new clutch pack screw washers, a new compression ring and a new clutch nut. A byproduct of the procedure was the elimination of rattle at idle in neutral with the clutch hand lever not pulled—the rattle that might be the source of @uldy's transient Brick-quality despair. Does this mean @auldy should replace those parts to find peace? To quote Joe Kenda, "Maybe."
I'll update this thread with the date, time, place, social circumstances and what I was wearing at the moment if the rattle resumes. If it hasn't been heard for 12,000 miles more, I'll post the news if such a benign sound manages to penetrate my state of equilibrium among rattles.
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The rattle came back on my K75 a couple years later and has been there since. It appears the torque works to stop it, but is only a temporary stopgap. If I ever go back in there again I will try putting some Loctite, either Red or Bearing Lock on the face of the clutch hub to help reduce hold the contact faces from moving relative to each other.
Will have to be careful not to get any Loctite on the clutch nut. With the torque on it, that red Loctite will effectively weld the nut in place.
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It was 10.31.2022 1500hrs at the entrance to the Wrightsville Reservoir picnic area on a solo ride, stopped on my idling Brick as I sought the address on my phone of a vehicle inspection station likely to approve my motorcycle's continued use without my waiting a week for the event, and while I was wearing a 12-year old Fox Creek Leather racing jacket, Scorpion Seattle overpants, EMS polyester cargo pants, a long-sleeve polyester jersey, an azure blue ExOfficio boxer brief with 4" inch inseam, a green Buff imprinted with the logo of the 2021 Montpelier virtual Corporate Cup Challenge and State Agency Race, Darn Tough hiking socks, TCX Explorer 4 vegan riding boots, a Diamond Silver Arai Signet-Q helmet and Firstgear insulated gloves, I heard the unmistakable faint rattle that might be the one plaguing @uldy. Once I realized it had returned, I greeted it happily like an old friend and the two of us roared up through the sweepers on Route 12, landing at the Worcester country store where I bought half a cup of coffee and possible future rights to simultaneous tax burden and tax relief. At Mazer Performance in Bolton, VT, my Brick passed its inspection with "flying colors." I flew home over the scenic pothole fields that are my town's roads.
Separation from the knock was brief and our reunion was ecstatic. icon_cheers
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A cupala days ago I was reading this thread and noticed a disagree comment was registered on the first post. I thought, how can you disagree with a first post, who would disagree with a first post? I clicked on it and it was me. I tried to undo it but couldn't. Not the first time I've done that either.
Musta been half asleep at the time, dunno.
Oops.
@uldy, I'm thinking your problem is likely to be a worn bearing more so than the tabs. There are past cases similar to yours; Rhoads rash, bgcameron, and MLR over at the K100-forum, to name a few. If the bearing is at the earliest stages of wear, then tightening the clutch nut could help, if very worn, the rattle would continue, regardless of how much torque is applied to the clutch nut.
I'm happy to be corrected, but I can't see how the tabs theory fits.
This problem has been solved in the past, buy replacing worn parts or torquing the clutch nut, but I don't think it's ever been fixed by altering the tabs.
Some people have reported no tab wear marks, I haven't found any comments that there was wear.
Cameron described an irregular clatter, sometimes just once while on level ground, but more when going slightly uphill. I don't think that should alter if it's caused by tabs banging around.
Let's say for a minute it is caused by power pulses banging the tabs around. At 3500rpm, it wouldn't knock just once out of thousands of pulses. Output shaft endfloat could match those symptoms though. With a three cylinder engine having one and a half power pulses per revolution, at 3500 rpm that's 5250 pulses. That's 87 clacks per second. I'm pretty sure he's not getting that.
I haven't found an example yet of an early model K75 with a high rev rattle from the output shaft, including yours. Don't know why they're always late models, but somewhere along the line the idle gear spring was replaced with a shim, but I've only read about a small number of the total cases.
In the design stage I think the K75 had an output shaft similar to the K100 but the absorber dampers just got knocked around too much due to the unbalance of three cylinders. So a balance shaft was chosen, good idea. One side affect of this afterthought is that it has lost the benefit of the extra diaphragm spring inside the absorber housing.
I think the only reason for the tabs is so that that balance weights are phased correctly. The tabs are offset so that the balance shaft can only be installed one way.
I don't think there's a BMW service bulletin about solving an output shaft noise problem by altering the tabs, but there is a service bulletin about replacing worn parts to solve this problem.
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I haven't found an example yet of an early model K75 with a high rev rattle from the output shaft, including yours. Don't know why they're always late models, but somewhere along the line the idle gear spring was replaced with a shim, but I've only read about a small number of the total cases.
I revisited this thread after rides on my 1993 K75S (11/92 - 81886 miles) and 1994 K75S (4/94 - 12768 miles). The '93 is smooth and quiet, the '94 has that annoying rattle at low RPMs. Beside the difference in fuel pumps there must have been other internal changes. Changed the monkey nuts and found the old ones in decent condition and cleaned the starter while I was in there. I knew it was probably not an easy fix from reading this topic some time ago.
The plan right now is just to leave as is and checking the output shaft when I do a full spline lube.
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Since that post I have seen at least one thread where an early model has had these symptoms, not surprising on second thoughts.
Since you have two bricks, basically the same, you're in a good position to do some simple tests. In one thread, a rattle problem was solved due to a loose spark plug lead. I spose you won't be that lucky, but a simple test would be to swap the plugs and leads around from one brick to the other to see if the problem transfers to the other brick.
I still only have a limited sample number to go by, but there have been cases where the rattle suddenly disappears at about 1,800rpm, and other cases where it suddenly disappears at about 3,700rpm. Some of the cases at 1,800 were solved, with work related to the auxillary shaft. Some of the cases at 3,700rpm were solved, with work related to the output shaft.