Bugger. Me clutch's gone? Or maybe not?

[Ixion]

Ah the wonderful controversy about the right gunk to use on BMW splines. I follow the heretics and use HondaMoly60.

But it is not the clutch thrust bearing that is suspect. The clutch cable connects to an actuating arm, pivoting at the rear of the gearbox. That arm runs across the bike in front of the rear wheel, and at the opposite end to the cable, bears on the clutch pushrod. (It's BMW. Expect wierd). The aforesaid actuating arm is pivoted on a shaft running crosswise, supported at either end by small needle rollers. These have no provision for lubrication, and have a history of breaking up . Which I suspect is what has happened, the needle rollers have snapped and every so often the bearing jams up on a bit of broken roller. Thus the actuating arm does not come fully back (there is no spring to return it, it relies on being pushed back by the clutch pushrod, good engineering Mein Herren) and the clutch is left slightly disengaged. Unfortuantely getting at the bearings is (apparently) a bit complicated, the footrest hangers have to come off, which means removing the exhaust, and the ABS units , and , and , and .

[Motu]

The BMW clutch spline lube issue has always puzzled me - it's an inline dry clutch drive,truely a 100 year old design that was perfected when Hitler was still in nappies.So how come regular clutch spline lube is a regular maintanence issue? Do you send your car in every year for the clutch splines to be lubed? This is a huge colosal fuckup from BMW and I'm surpised some Yank hasn't taken them to task over it.How can you fuck up something the rest of the industry has been doing perfectly for 100 years?

[Ixion]

Well, an update, an possible explanation.

The odd slipping did not reoccur. But, I started to observe slight clutch slip of the "normal" variety. Not bad but there.

And coupled with the lingering suspicion, and a twitching conscience about not yet having lubed all those splines. Or checked the universal joints.And fretting about what condition they might be in (Just don't start me off on this one - like Mr Motu I cannot comprhend how BMW can get away with it. Millions of cars on the road with the same arrangment , not one of them needs the transmission pulled apart every year for lubrication)

So, I decided I'd better summon up my courage and pull it down.

Not too bad actually, the actual clutch/gearbox bit is pretty straight forward. Bad bit is the amunt of stuff you have to pull of to get there, including FI computer, ABS computer, ABS units, wheel sensors , all sorts of "don't come near me if you know what's good for you" stuff.

Finally pulled the gearbox out, and stripped out the clutch.

No sign of oil, a bit of thick dust , but no evidence of leaking from either end.

Mic'ed the old plate , only 1 mm under standard. Hmm, 1mm isn't a lot of wear, could that account for the clutch slip? Until I compared it with the new plate. Hm, yes, 1 mm IS a lot of wear when you're talking clutch plates. The friction plate was worn bevelled too, nearly 10 thou difference between inner and out circumferential thickness. Not good ,that, and the clutch friction hub isn't sprung so there's no give to take it up. Very crude clutch looks like something out of a Model A Ford.

But, looking at the old friction plate I think maybe I see the reason for the original strange behaviour. In one face of the clutch plate , there are a lot of deep gouges and scores. I do mean deep, nearly through the thickness of the friction lining. Not much surface area in aggregate, but quite a lot of them .Only thing I can think of doing that sort of damage is a small hard foreign body getting between the friction plate and the pressure plate. Keeping them from making proper contact until the foreign body is either forced into the friction material (hence the gouges) or spat out. But until then, the clutch plates would hardly touch at all.

Certainly nothing like any normal sort of wear. *Very* thorough examination of all the bits shows no sign of any broken off metal bit that could account for it. But, grubbing about in the recesses of the bell housing casting I extracted a number (about a dozen) small hard granitey stones, up to maybe 3/16 diameter (though not circular). Guess one of them could have done the job. How did they get there. Only thing I can think of is they came in through the largish drain hole at the bottom of the bell housing. I guess that on gravel roads, or roadworks (some appeared to be tar coated) the bottom of the bike must be subjected to quite a fusillade.

The pressure plate when carefully straight edged showed several thou deformation on the mounting tabs. so I replaced it too. If I'd been on a tight budget , I'd have just dressed the tabs down with a fine file or a surface plate. But I was lazy , and did it by the book. Other than that , only parts required were 6 retaining allen bolts and 6 shake proof washers for ditto . All ex stock at Experience BMW. Who kindly gave me sufficient of the super duper special BMW spline lubricant , for free, to do all my splines. Very kind of them, it's pricey stuff and a whole tube would last a lifetime..

Oh, my splines were perfect , as were my universals. No wear at all.

I pulled off that suspect linkage arm. It felt dry and stiff though not rough. No grease nipples or provision for lubricating it.(grrr. Can I have a word , Mein Herr Designer) . So I did the old trick of boiling it up in a pot of grease. Felt much better after that . Smelly business though, hopefully Mrs Ixion will start talking to me again in a few weeks time.

Reassembly was straight forward, other than having to turn up a mandrel to centre the clutch. I did a dummy run by eye, but decided the mandrel was a neccesity. The official BMW tool is a pretty thing, got knurling on the handle and everyfing fancy like, but costs nearly $100. Hm, too rich for my pocket book, bit of gash steel and a couple of hours on the lathe, it's a crude thing at best, but then so am I. Worked fine.

I priced the parts up at Motobins in the UK BTW, would have saved a bit , though not so much cos freight is high on such heavy stuff, and I didn't think it worth the wait.

All the bits that came off went back on without arguing (very unusual that for German parts) , and everything worked once it was back together. Including the ABS which i was very worried about.

Couple of hundred kilometres on it now, no leaks, bits come off, noises or other BadThings. And the clutch is now full of clutchy goodness. Very slight judder, but i'll put that down to bedding in. The gearchange seems a lot smoother too, might be because the clutch is taking up earlier, but probably just imagination. Clutch action is definately lighter. Maybe the greasing of the linkage arm, or maybe cos I left off the stupid linkage that is supposed to pull the side stand up when you pull in the clutch. I've no time for such idiot features.

Just need to do a recheck on nuts and bolts being tight, and I'll say the mystery is explained.

Oh, and I've blocked that drain hole up with a wodge of foam. Should still let any oil or water drip out, but prevent the ingress of foreign bodies.

[Motu]

I wonder how they make brake and clutch lining material? Like do they have a big pot of the brew,is it turned widershins with three eyes of newt? Often we find bits of hard material imbeded in disc pads (said newt eye?) and of course these days it's our fault.But because dry clutches last longer than brakes and are not a component you can have a quick look at (unless you pop your box out after work for a quick spline lube) all sorts of mayhem can go on un noticed.After doing many car clutches over the years I've seen just about everything - most just wear out to various points of failure,but some in exact same conditions can show heavy grooving.It must be caused by either soft parts in flywheel and pressure plates or hard spots in the lining material,hard spots in the lining material is the obvious choice.It's a random event,but I've never heard of it causing clutch slip.I've picked some pretty big chunks out of disc pads,no reason why they wouldn't be in a clutch plate.

[Blackbird]

Fascinating account Ixion and glad that it seems to have paid off. I'm glad that I didn't read this when I had my K100RS. I owned it for 8 years and never went near the clutch or actuating mechanism. Other than the known intermittent instrument housing electrical problem which I eventually fixed and some slight cracks in the rear disk (another known problem), it just ran and ran. (Oh, and the 3 months it took me to discover that petrol lead substitute additive was blocking the tank filter, but that's another story).

[Ixion]

It's possible that it could have been a hard inclusion in the friction material that worked loose. The gouging didn't run the full way round the plate, and wasnt in neat annular grooves. It looked like someone had taken to the plate with a screwdriver and dug bits of lining out of the plate.

I've seen annular grooves in clutches many times - this was quite different. There was no grooving or damage to the pressure plate at all, apart from the slight distortion of the mounting tabs.

I've also known a clutch clip when a bit of lining got ripped loose and turned back on itself , which I guess is a similar thing.

Certainly something hard seems to have gotten between the plates at one point in the past, and then been eliminated. (Though that would not have caused the slight "normal" slip, that was just wear)

[merv]

Geez hearing about the stones inside the bell housing makes me glad my bikes all have wet clutches safely tucked away from the elements.

Closest I've suffered to that story is we had a 1981 Honda Accord from new way back then and it had a bad habit of picking up those kinds of stones on fresh seal etc and getting them stuck between the front brake discs and the backplate cover and then they'd grind away and make a godawful noise until you got them out.

[Blackbird]

Closest I've suffered to that story is we had a 1981 Honda Accord from new way back then and it had a bad habit of picking up those kinds of stones on fresh seal etc and getting them stuck between the front brake discs and the backplate cover and then they'd grind away and make a godawful noise until you got them out.

My wife's MX 5 does that all the time. Stopping and reversing for a few metres works on most, but not all occasions.