BMW K bikes (Bricks)

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Kafflut

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The rattle is only at low revs. It seems to come from the rear, not the timing chain end. When I pull the clutch lever it is less noisy, but still there. At higher revs, I'd say anything over about 1700, it goes away.

A very useful article : http://www.ibmwr.org/ktech/output-shaft-noise.shtml

Number 6 under the heading  "Begin"  reads: "Insert a bar or screw driver shaft into the water pump end of the output shaft. It should slide far enough into the shaft to ensure it will not slip out when engine weight is applied to it. Using crate straps, or similar strap (I used a cargo strap) loop one end around the output shaft, and secure it to the frame. Loop another cable around the protruding bar (or screwdriver) end on the front of the output shaft and secure it to the frame. The absorber gear and idle gear are under tension and we do NOT want the tension to force the output shaft out on us when the lower engine case is removed! The rear crate strap is going to support the weight of the engine, when you remove the transmission jack… make SURE it is tight and secure!"

I don't quite follow this. A photo would help a lot. I expect I'll have a clearer understanding when I get there.

Q1. Would it be possible to check the condition of the rivets without removing the output shaft? ie Could I check for wear before removing the "transmission jack"?

http://bmwk100k75.weebly.com/
    

charlie99

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yes ,
you can see the output shaft  through the crankcase cover  removed , although  you may need a torch if under cover

what you will see is the aluminium basket to counter gear ...and what to look for is movement between the two parts

select 2nd gear and rotate the rear wheel back , forward whilst on the centre stand .

hope that helps

btw even removed , because the backlash tensioner covers the face of the rivets its hard to see exactly the amount of wear into the basket that has occurred

you need to pull the bearing that fits infront of the backlash gear to remove it ,

from the basket end you may be able to see the wear and movement of the rivets


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'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%O
    

Kafflut

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Thanks Charlie. Can you confirm, in the event that worn rivets is the problem, although a bit tight, I should be able to detect "movement between the two parts" if I remove the crankcase cover and look in as shown in the photo below? ie the gear in the foreground and plainly visible meshes with the "counter gear" below and I should be able to detect movement through the tiny gap if I peer along the red line?

If the above is possible it makes the job of diagnosing a lot smaller - I don't have to drain the oil or the coolant or remove parts other than the crankcase cover  cheers And that appeals to me. In this photo the crankcase has been rotated without removing the hose at RHS

http://bmwk100k75.weebly.com/
    

charlie99

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nearly right
you can see it on the right hand side of the big gear

the meshed gear being the backlash on the left hand side  will be meshed so you wont see any movement there '

but it is recommended on any rebuild that the spring to the backlash gear be inspected ...and depending on model ie early types 84-86  replaced with the newer slimmer type , often the hole that the backlash spring fits into expands and wears past its spring limit . but as said before you cant see it till it is removed and bearing pulled .

what year model is this one ?


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cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%O
    

Kafflut

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@charlie99 wrote:but it is recommended on any rebuild that the spring to the backlash gear be inspected ...and depending on model ie early types 84-86  replaced with the newer slimmer type , often the hole that the backlash spring fits into expands and wears past its spring limit . but as said before you cant see it till it is removed and bearing pulled .

what year model is this one ?

I think it's a 1986 - I can't be sure because I bought it as a scrapped after collision bike with no paperwork, I have not done a search on engine number & year of manufacture, I have that replacement spring in case I need to pull out the output shaft for rivets. I'm hoping though that the rivets are okay.

Bur now I'm thinking, maybe I can make an assessment without even taking off the crankcase cover !! The other end of the output shaft drives the water/oil pump, doesn't it? Let's expose that end - I should be able to see any play if I do your suggested second gear wiggle. I mean, I don't need to actually see the aluminium basket and or the rivets - if the water pump end of the output shaft is dead still when I do the second gear wiggle I'll know the rivets are not holding the basket tight onto the gear.

What do you think of that idea?

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charlie99

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hmm could be hard to see as the rivet movement is quite small …..but you might be able to feel the slop ….or if you get a wide blade screwdriver you might be able to wiggle the shaft to pick up the movement from behind the water pump .


good luck


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cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%O
    

Kafflut

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All my trying to avoid removing the crankshaft cover was nonsense. I have to remove it anyway, I realized in the end; it's been scratched and has to be repainted. So I removed it and checked for "movement between the two parts", gear and aluminum shock absorber body - I'm using the Haynes terminology.

The way I did it is to cautiously wedge the tail end of a file between A(casing edge) and B(shock absorber wall) - see image below. I figure if I now wiggle the gear, move it a little and the shock absorber body doesn't move I have a rivets problem.



I moved the engine using an allan key in the ignition timing plate bolt - I've never been able to move the engine successfully to find tdc by turning the back wheel.

My "wedge" was now blocking my view of the shock absorber body where it's attached to the gear, but I used an opening a bit further to right and by shining a torch in there I could see what the shock absorber was doing when I moved the engine - you really need an extra hand.



The shock absorber body moved with each tiny engine movement. So now, have I confirmed that the rivets are okay? I don't know. I think so.

If I had moved the back wheel the movement would be transferred via gearbox to the output shaft spline to the drive gear and finally the shock absorber housing( I think).

What I actually did was move the engine. The engine movement is then transferred to the drive gear and from there to the aluminum shock absorber( I think).

I hope this makes sense.

I may still have a problem with the anti-backlash spring, but that can wait for now.

Charlie, I'd appreciate your feedback/suggestions.

http://bmwk100k75.weebly.com/
    

charlie99

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often its the noise generated within the motor is the thing that folks are chasing , and as you say the spring in the antibacklash can be a source of noise if worn , along with many other bits and pieces (sprag clutch - auxiliary shaft , alternator drive bushes , starter idler gear and the list goes on .)

, there still maybe some movement in the basket damper assembly - rivets  ,

but It means that it will run ok for a good deal of time more if your happy that nothing will break in the process .

the noise at idle is often the indicator that the damper basket rivets are indeed loose or wearing badly , its to do with the nature of the 180 degree crank and the timing of the acceleration of the output shaft at the ignition stroke .combined with a quite large rotating mass at the end of the output shaft namely the clutch assembly

I recon there are components that may contribute to the rivet failure , the dampers within the basket may have shrunk ? allowing slightly more movement ...then allowing a flogging process to start

im reminded when I rebuilt my assembly my dampers were indeed loose to some degree ,but the rivets were showing lots of movement along with noticeable wear marks on the drive gears at about 90  (oops )180 degrees to each other ... unfortunately during the rebuild I didn't replace the dampers  (none on hand ) , I should have done so to extend the life of the repair that alby and I did .about 4 years ago now and probably a good 50- 60,000 kilometers ago) ( alby had offset redilled the basket and installed bolts through the assembly to the drive gear off the main shaft through new aluminium metal of the basket ).
 I was so fortunate that he (alby ) passed on the modified gear to me at that time . with many many thanks to alby

my output shaft is now showing some rattling , but nowhere near as bad as when we changed the assembly ….yet !!  but im sure the damper inside are just about cactus as im experiencing some harmonic vibrations right about 3700 through to 4200 revs ...and heavy vibration at about 3000 on deceleration  

also timing chain tensioner  issues could be adding to this noticed vibration on deceleration

throttle body balancing could maybe minimise the heard rattling  and also make sure that the breather tube crankcase to plenum is in good order . seriously noisy idling can be caused by this tube  airleak . 

to confirm the breather being bad ...remove the engine oil filler cap whilst idling and if it makes more noise then the breather tube is likely ok ??  but worth inspecting regardless

just some thoughts

I hope it helps



Last edited by charlie99 on Sun Jul 01, 2018 2:57 am; edited 1 time in total


__________________________________________________
cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%O
    

Kafflut

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@charlie99 wrote:often its the noise generated within the motor is the thing that folks are chasing , and as you say the
the noise at idle is often the indicator that the damper basket rivets are indeed loose or wearing badly , its to do with the nature of the 180 degree crank and the timing of the acceleration of the output shaft at the ignition stroke .combined with a quite large rotating mass at the end of the output shaft namely the clutch assembly

.......... ...then allowing a flogging process to start

I hope it helps

Iit helps much. I have a better grasp of what happens there and understand why the noise would be more pronounced at idle revs.

Thanks for your help - I now have the confidence to examine my other machine, the noisy one.

In my search for information I found a YouTube that illustrates the rivet problem well. It may help others - here it is

http://bmwk100k75.weebly.com/
    

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