Author Topic: 1989 K75 engine rattle/knock.  (Read 40666 times)

Offline cycle thread

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1989 K75 engine rattle/knock.
« on: November 26, 2015, 02:51:07 PM »
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
  • Somerset United Kingdom
  • 1989 K75 Low Seat

Offline F14CRAZY

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Re: 1989 K75 engine rattle/knock.
« Reply #1 on: November 26, 2015, 03:41:47 PM »
Could be the rubber alternator drive nuts ("monkey nuts"). Remove your alternator and start it up and see how it sounds
  • Grand Rapids, MI
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Offline cycle thread

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Re: 1989 K75 engine rattle/knock.
« Reply #2 on: November 28, 2015, 06:16:52 PM »
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
  • Somerset United Kingdom
  • 1989 K75 Low Seat

Offline The Mighty Gryphon

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Re: 1989 K75 engine rattle/knock.
« Reply #3 on: November 28, 2015, 08:43:28 PM »
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.   
  • In my garage in Marilla, NY
  • '91K100RS White/Blue
Current:
'91 K100RS16V "Moby Brick Too"

Past:
'94 K75RT "Ilsa, She Wolf of the SS"
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"

Offline darthbane71

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Re: 1989 K75 engine rattle/knock.
« Reply #4 on: November 29, 2015, 06:44:32 PM »
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?
  • Illinois
  • 93 k75RT, 97 Yzf600r, 80 cb650c, 81 cm400
1993 BMW K75RT

Offline darthbane71

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Re: 1989 K75 engine rattle/knock.
« Reply #5 on: November 29, 2015, 06:51:58 PM »
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.
  • Illinois
  • 93 k75RT, 97 Yzf600r, 80 cb650c, 81 cm400
1993 BMW K75RT

Offline Scott_

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Re: 1989 K75 engine rattle/knock.
« Reply #6 on: November 29, 2015, 07:01:13 PM »
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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Offline The Mighty Gryphon

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Re: 1989 K75 engine rattle/knock.
« Reply #7 on: November 29, 2015, 08:00:08 PM »
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.

  • In my garage in Marilla, NY
  • '91K100RS White/Blue
Current:
'91 K100RS16V "Moby Brick Too"

Past:
'94 K75RT "Ilsa, She Wolf of the SS"
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"

Offline cycle thread

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Re: 1989 K75 engine rattle/knock.
« Reply #8 on: December 02, 2015, 06:03:25 AM »
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

  • Somerset United Kingdom
  • 1989 K75 Low Seat

Offline Rhodes rash

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Re: 1989 K75 engine rattle/knock.
« Reply #9 on: January 15, 2016, 06:10:58 PM »
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
  • Lumby, B.C., Canada
  • 1991 K75RT... Have had a bunch of other bikes stretching back to (excluding wee Suzukis in the '60's used for summer job transport) '72 Triumph Bonneville 650. Bonneville 750, Triumph Trident 750, Moto Guzzi 850 T4, BMW K75C

Offline Laitch

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Re: 1989 K75 engine rattle/knock.
« Reply #10 on: January 15, 2016, 06:32:03 PM »
What would be helpful would be for you to post an mp3 recording of the sound before you do the work.
  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles
I wept because I had no radials until I met a man who had no splines.
https://tinyurl.com/RillRider

Offline Rhodes rash

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Re: 1989 K75 engine rattle/knock.
« Reply #11 on: January 15, 2016, 11:00:28 PM »
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.
  • Lumby, B.C., Canada
  • 1991 K75RT... Have had a bunch of other bikes stretching back to (excluding wee Suzukis in the '60's used for summer job transport) '72 Triumph Bonneville 650. Bonneville 750, Triumph Trident 750, Moto Guzzi 850 T4, BMW K75C

Offline darthbane71

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Re: 1989 K75 engine rattle/knock.
« Reply #12 on: January 15, 2016, 11:05:17 PM »
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. 
  • Illinois
  • 93 k75RT, 97 Yzf600r, 80 cb650c, 81 cm400
1993 BMW K75RT

Offline Rhodes rash

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Re: 1989 K75 engine rattle/knock.
« Reply #13 on: January 15, 2016, 11:33:46 PM »
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:
  • Lumby, B.C., Canada
  • 1991 K75RT... Have had a bunch of other bikes stretching back to (excluding wee Suzukis in the '60's used for summer job transport) '72 Triumph Bonneville 650. Bonneville 750, Triumph Trident 750, Moto Guzzi 850 T4, BMW K75C

Offline darthbane71

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Re: 1989 K75 engine rattle/knock.
« Reply #14 on: January 15, 2016, 11:35:00 PM »
Ive had similar problems with replicating the noise while not moving but I'll give it a try
  • Illinois
  • 93 k75RT, 97 Yzf600r, 80 cb650c, 81 cm400
1993 BMW K75RT

Offline The Mighty Gryphon

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Re: 1989 K75 engine rattle/knock.
« Reply #15 on: January 16, 2016, 09:12:21 AM »
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.
  • In my garage in Marilla, NY
  • '91K100RS White/Blue
Current:
'91 K100RS16V "Moby Brick Too"

Past:
'94 K75RT "Ilsa, She Wolf of the SS"
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"

Offline Rhodes rash

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Re: 1989 K75 engine rattle/knock.
« Reply #16 on: February 16, 2016, 10:53:21 PM »
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.
  • Lumby, B.C., Canada
  • 1991 K75RT... Have had a bunch of other bikes stretching back to (excluding wee Suzukis in the '60's used for summer job transport) '72 Triumph Bonneville 650. Bonneville 750, Triumph Trident 750, Moto Guzzi 850 T4, BMW K75C

Offline gone_ape

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  • 94 K75RT (Now Standard)
Re: 1989 K75 engine rattle/knock.
« Reply #17 on: May 30, 2016, 01:58:15 AM »
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?
  • Austin, TX
  • 94 K75RT (Now Standard)

Offline K1300S

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Re: 1989 K75 engine rattle/knock.
« Reply #18 on: May 30, 2016, 06:58:59 AM »
Mine has same noise.  Resigned to pulling the engine later this year to fix.    Sigh.  Only about 30k miles on engine.
Project Thread "K75s Midlife Refresh"
http://www.motobrick.com/index.php/topic,7810.0.html

Offline Laitch

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Re: 1989 K75 engine rattle/knock.
« Reply #19 on: May 30, 2016, 07:00:39 AM »
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?
  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles
I wept because I had no radials until I met a man who had no splines.
https://tinyurl.com/RillRider

Offline gone_ape

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Re: 1989 K75 engine rattle/knock.
« Reply #20 on: May 30, 2016, 12:36:08 PM »
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....

  • Austin, TX
  • 94 K75RT (Now Standard)

Offline Laitch

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Re: 1989 K75 engine rattle/knock.
« Reply #21 on: May 30, 2016, 01:29:06 PM »
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.

  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles
I wept because I had no radials until I met a man who had no splines.
https://tinyurl.com/RillRider

Offline The Mighty Gryphon

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Re: 1989 K75 engine rattle/knock.
« Reply #22 on: May 30, 2016, 02:25:04 PM »
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. 
  • In my garage in Marilla, NY
  • '91K100RS White/Blue
Current:
'91 K100RS16V "Moby Brick Too"

Past:
'94 K75RT "Ilsa, She Wolf of the SS"
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"

Offline gone_ape

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Re: 1989 K75 engine rattle/knock.
« Reply #23 on: May 30, 2016, 02:29:08 PM »
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?
  • Austin, TX
  • 94 K75RT (Now Standard)

Offline gone_ape

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Re: 1989 K75 engine rattle/knock.
« Reply #24 on: May 30, 2016, 02:33:24 PM »
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!!
  • Austin, TX
  • 94 K75RT (Now Standard)

Tags: 500rpm to 3 700rpm