Hi guys,
I am trying to assist a fellow ex African with a high mileage machine -240k km - that sounded from his description to have the much talked of K rattle.

Vin number is 0106669 12/88

Clutch nut was bloody tight

Bearings all look fine

Spring and pins look fine - no sign of anyone else having been in there

Cleaned everything and reassembled without the C spring in order to measure the end float with feeler gauges and there is none. It feels like the main gear and anti backlash gear are preloaded by too big a shim. i.e the inner race of the ball bearing is up against the shim instead of being up against the locating shoulder so the new style circlip is preloading the gears. Can this bike have done all those kms and then start making a rattle when everything looks fine except for there being no end float?
PO - sold it for a song because he said he didn't have time to fix the rattle. The rest of the bike is mint condition - idles ok and runs smoothly.
Just rattles at +- 3500 rpm or some such according to my mate.

He will email me photos to put up tomorrow.

Any ideas?

rawdon ....I don't think the k75 has the damper installed at all ...which is where the rattle that the k100 develops originates from ( the rivets holding the basket - damper)

perhaps a good look at the bmw fische  parts diagrams might clarify this for you

the workshop manual available from the downloads section for the k100 also details the k75 output shaft

hope that helps some.

Here's the ETK for a 1st month build of '88 K75S   (not 12th) of the engine and shafts, etc., using that model's VIN. It could be something relatively minor like the rubber moneky nuts, or a worn gearbox bearing...is the noise while under load, neutral throttle or free revving?

No damper on k75 as you say Charles. We have the balance shaft in pieces and need to understand this preload of anti backlash gear problem (preferably) before finalising the rebuild and check to see if noise has gone away. 

Monkey nuts are good

Thanks for ETK TWB  - haven't heard the noise myself but gather it is not very predictable. Mechanic rode it round the block and said he heard nothing!

HAYNES says to measure distance from backlash gear face to bearing inner race when positioned against locating shoulder and calculate shim required to give 0.01 to 0.15mm clearance. 

This is why the presence of backlash gear preload with existing 1.15mm shim is confounding us - photos to be posted today will show

for what its worth rawdon

whilst doing my output shaft

we noticed a definite sharks toothing of the output shaft gear faces ....well that doesn't explain it well but a similar type of non conformity where the leading edge of the gears was worn away quite markedly ...

I guess creating a tiny bit of slack between each of the gears ...I would think this might be a contributing factor ?

think I have a pic here to explain ...hang on






what im trying to say is that we noticed some wear in the gears allowing some movement between them


thought it might be worth looking at whilst it is apart

Could also be a idea to change the c-clip, it happens that they lose some of
their tension over time, also check that the mounting pins isn't worn.

If that doesn't help, coat both sides of the c-clip with blinker fluid.

I think we have nailed down the problem. 

Anti back lash gear installed at factory was approx 2 thou (0.08mm) too thick. 

The  annular contact ring on the face of the main gear has variable hardness due to the heat treatment of the gear teeth - hence the wear rate varies and the contact faces end up with a series of bumps and troughs. 
T
Thus it becomes progressively more difficult for the C spring to get the anti back lash gear to adjust to the position required for cold running. 

Fix: 
Lap the end float shim to give the required clearance. 

Drive out the pin in the back lash gear and lap contact face to obtain plain surface 

Use back lash gear to lap contact face of main  gear in the hope of removing the high spots 

Clean carefully and reassemble

If it is still noisy - resort to BLINKER FLUID

ANY COMMENTS BESIDES THE COLOUR OF THE REQUIRED BLINKER FLUID?

Forget the blinker fluid. Ask yourself the obvious question:

Ok so the blinker fluid is to cool the bulbs and the roller bearings in the muffler when we fail to regrease them is why they make that rattling sound when going up the hill, silly me I took the black cover plate off mine to stop the rattle maybe I should get the grease gun, Where is the grease nipple in these mufflers anyway

They don't have a grease nipple, you have to get a new replacement unit to upgrade the complete bike to a K1300GT, they are available from your ever so friendly BMW Dealer for $27,000 + the cost of removing your trade from the showroom floor.

$27 ! yikes, might bribe Alby he's had afew apart, he might have a spare bearing, now the part number for dry bearing grease would be?