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Old 5 Apr 2002
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Posts: 71
R80G/S g/box input shaft -clutch centre splines

when checking the clutch plate (100km)i noticed the clutch plate will tilt/rock at the edge approx 3mm .a new clutch plate does the same, this is because there is a slight taper on the g/box input shaft ,max. 0.25mm, towards the g/box end of the shaft .
a R100GS rider has a similar amount of play.
in operation does this matter?
is this "standard" ?
i'm getting my bike ready for a big trip ,do i need to replace the g/box input shaft ?
thanks for any advice
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Old 10 Apr 2002
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Location: Bärenklau, Brandenburg, Germany
Posts: 9
hi bryan,

i'm not sure where exactly the 'play' is that you observed. thats what i've understood: you removed g/box and clutch. you put the clutch plate on the inshaft. now it's possible to tilt the clutch plate? is it tilting on the shaft or is the shaft tilting in its bearing? or is it an axial-play (back and forth) only of the shaft? what do you mean by "a slight taper on the shaft"? does it mean, the diameter of the shaft is a little bit thinner towards the g/box side? or is there something like a "notch" (im not sure about the word) around the shaft's "teeth" (again not sure)?

my english tech-vocabulary is not very well and my dictionary is only a small holiday one. so i'm not sure to understand your problem and hope you understand my questions. on the website of "ulis motorradladen" (http://www.ulismotorradladen.de) you find explosion-drawings of any bmw-part from '49 to '96. but 70's to 90's only in the german version (choose german version and click on "rißzeichnungen"). these drawings may help to explain the problem.

i'm riding bmws for 17 years and never heard of real g/box problems (bearings and stuff). but at early 80's bikes there was a problem with the "teething" of the clutch plate: it "looses its teeth" very fast (once i removed such a clutch of an unknown r80g/s-rider on a dirt track in algeria - much fun after a german 4wd with iced stopped to "help" us ...).

if there is no tilting of the shaft in its bearing and the teeth of shaft and clutch plate look alright, i would put everything together and go anywhere in a range of - say - 30,000 km whithout one thought. a friend of mine once lost the g/box oil drain plug (r60/7) on the way home from greece and realized it in germany - without any harm to the g/box. these bikes (especially the 70's and 80's models) are designed for heavy duty ...

long may you run
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Old 10 Apr 2002
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Location: Boulder, CO USA
Posts: 6

I'm not sure of the amount of play that there should be, but I can tell you about my experience with my '81 R80G/S.

The gearbox input shaft splines stripped on my bike atabout 75,000 miles. I started noticing some extra vibration before the splines went. I thought I was imagining it, but when the bike stopped moving forward I knew exactly what had happened.

When I removed the gearbox there was obvious wear patterns on the shaft splines where the clutch plate mates to the shaft. That is, the shaft splines were worn lower where the clutch fit than closer to the gearbox. Obviously, my shaft was stripped so there was bound to be damage, but you might be able to examine your shaft to see if you notice any obvious damage or wear.

If I were taking a long trip on the bike and I had the gearbox out, I would probably replace the input shaft just to be safe. Especially after my experience that suggests they may go at 75k miles.

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Old 15 Apr 2002
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gerd , story, thanks for the replies.
orginally i stripped the splines out of the clutch plate centre - bone dry no grease or lubrication on assembly - thank you bmw!!.
to get going i fitted the spare clutch plate i had - greased of course .
a few k's later i dismantled the clutch to check on the "new" plate ,no problem ,very smooth operation but i noticed this tilt of the clutch plate on the g/box input shaft.
there is no play on the g/box bearing but minor wear on the odd spline grove.
that was 30000miles ago.
other air-head twins "seem" to develop this clutch plate /g/box shaft tilt ,i was hoping somebody with a high mileage(100,000?) could advise if this "wear" is likely to cause a breakdown .
does anybody know the "new"size of the g/box input shaft? and it's manufacturing tolerance?
thanks bryan
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Old 16 Apr 2002
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Join Date: Dec 1997
Location: Vancouver BC Canada
Posts: 4,560

A slight "tilting" of the clutch plate - as I understand what you're doing - would be normal - there has to be some play or you'd be at severe risk of binding. 3mm at the outside of something the size of the clutch disk doesn't sound particularly excessive.

Looking at my own 130,000km input shaft and another one beside it with less, there is NO taper of the splines, nor should there be. My splines measure out at 23.51mm max dia. - at both ends of the splines - 0 taper. That's at 130,000km.

(Gerd, for your information - your "teeth" in this case are technically called "splines" but "teeth" is understandable. Splines are finer/smaller than teeth and are used in this design of a shaft into clutch, whereas teeth are on the gears in the transmission and mate with another gear)

The input shaft spline wear is a well-documented and frequent problem. The splines should be greased with a good anti-seize about every 25,000 miles or less.

>>100km (is that km or miles - don't know where you're from - click on "profile" to fill that in)

If there is tapering, or any sign of wear on the splines, it's time to replace the shaft.

Also, replace all the ball-bearings. The roller bearing on the input is probably fine for a long time, but the ball bearings have been known to fail with regularity. Mine did recently at 100,000km on it. Many mechanics figure that it's a "regular maintenance" job to replace the bearings and inspect every 100,000km or 60,000 miles for normal use. Then someone will come along and tell you that's nonsense, they got 250,000 on theirs and it's still fine. Always someone who breaks the rules and gets away with it!

I'm very easy on my gearbox, smooth shifting and I don't lug it etc, replace oil at every service, and it still blew the large ball-bearing spectacularly, wiping out almost everything. Sad - the gear dogs were almost like new, no significant wear at all - but the teeth were chewed up by the shrapnel circulating. The splines are still perfect, but they were lubed at 25,000km intervals. The clutch is perfect, less than half-worn. In fact I find it amazing that people carry spare clutch plates as long as they know to look at their splines and lube them occasionally.

Hope that helps,

Grant Johnson

One world, Two wheels.
Grant Johnson

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