k75 clutch problem

[kettle]

I am the Australian (Tasmania) owner of a K75 (12/86 model) and have a question for your technical department.

I have owned the bike since 1995 when it had 47,000kms on the clock. It has been, without doubt, a wonderfully reliable, efficient bike. I have had to spend almost
nothing on repairs over the years apart from this ongoing problem. I have used the bike extensively to commute (not since 2001) and to tour the country. We live on a mountainous island with superb
roads for motorcycling. I have not thrashed the bike, but cruise at around 5,000rpm all the time and can average in excess of 100kmh wherever I ride. I have never topped up the coolant or ever topped up the oil
between changes  - a remarkable feat, I think. I have a few minor items replaced over the years, but the engine is untouched, as is the starter, final drive and alternator.

At 133,000km, the clutch failed. When we dismantled it, the spline had sheered off inside the clutch plate and damaged the input shaft. I had both replaced and continued on.
3 years later at 160,000km it did the same thing again and yet again at 213,000km.  As the cost of the input shaft is so high, a local engineer built it up and re-cut the splines. This lasted until 2015 at 229,000.
At this point, I decided to purchase a second hand gearbox (cost again), making sure that the clutch plate was a tight fit on the spine. The new gearbox was an improvement on my old one, having done half the mileage.
However, whilst riding steadily in top gear up an incline last week, it died again having only done 4500km since the last change.

Prior to previous failures, there had been a slight chattering when idling,  which a couple of clutch lever actions would usually make disappear. This warned me of impending failures, but this time did not.
The local mechanic told me last time that lack of dowell pins between the bell housing and motor can possibly cause  this, but mine are in place.  I have spoken to the senior mechanic at the local dealer, who
did the first repair. He has only ever experienced one other similar problem, but that was a one off and not an ongoing one, as is mine.

I have heard talk of some Australian bikes being mishandled when shipped into the country on slings, but this is just hearsay. I would be very pleased if you could offer some advice on what my problem may be.
I do not want to retire the bike yet - I think it still has a lot of km left in it.

Look forward to your response.

[daveson]

Slings at the docks wouldn't cause damage there.

I'll guess you didn't grease the clutch splines, then that's not too bad km. especially If the previous owner also didn't do it.

So then its possibly something wrong with the installing. Not sure if you did it, or a mechanic.

I'm trying to think of a way with a dial gauge or feeler gauge to check the clutch install is true.

There are dowels for the clutch housing  too, have a good look at them, and both bell housing faces, thinking something hasn't been put back right.

[The Mighty Gryphon]

Welcome!

First thing that came to mind when I read your post was whether or not you have ever lubed the clutch splines.  It's an important item, that seems only to be word of mouth among brick owners.  It's important for smoother downshifts, as well as preventing wear on the clutch splines.

Is there any roughness or slop in the bearings on the input shaft?  Were they replaced with the input shaft?

Beyond the spline lube, I seem to recall reading on one of the brick forums about a bike that had a misaligned transmission.  I can't recall how it was determined or what the cause of the misalignment was.

[Laitch]

The local mechanic told me last time that lack of dowell pins between the bell housing and motor can possibly cause  this, but mine are in place.

There are also two dowel pins between the bell housing and the transmission. You should verify that the local mechanic saw those,

[Arktasian]

That bulletin advises .25mm ( = 10 thousands") which strikes me as an awful lot. There are ways to mount and dial in both sides of the engine/ tranny joint, further proven with a tranny case emptied of content and measure through the input bearing bore while on the dowels. Not sure if either or both sides of that joint are blind holes for the dowels, but if open on one side then a corrective drilling and O.S. dowel can be installed to maintain corrected concentricity via the bolt circle tightened,  initially.
(I've found as little as 4 thou run out on a boxer bell housing and corrected on the contact lugs with metal compound (those don't use dowels).
 More than one way to skin this cat but I'd recommend holding the K closer to 3 or 4 thou max.

[daveson]

Are you confident the clutch balance marks went back the same way? There was a case here with an unbalanced one causing noise but not vibration.

I dread to mention this but after checking gearbox input shaft bearings, check the engine output shaft for play, axial and longitudinal.

[kettle]

Thank you all for your input. I will check all the dowells again and try to check run out on the shafts. I am no mechanic, but my son is and we spoke to the local bmw expert at last time of fitting. Checking run out  was not discussed, but THIS TIME we will be more careful!!