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  #16  
Old 30 Sep 2012
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The gearbox of my R80GS had to be rebuilt at 18,000 kms. Once open I decided to have the shorter 1st and longer 5th fitted, and exchanged the clutch for the ceramic type. Regarding fuel consumption it didn't make any difference, but I love the lower 1st. It allows you to approach tricky road conditions fairly slow.

Meanwhile the bike has done 150,000 kms and is still going very well. IMHO the best of the above changes is the ceramic clutch. Probably it will outlive the bike

Hans
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  #17  
Old 1 Oct 2012
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Improved fuel economy with taller 5th gear

Maybe.

It's really a matter of the engine's torque curve and at what MPH the flat part of that curve will be achieved. Typically, engines provide optimum mileage in a range of the curve which appears rather flat, like a stylized mesa.

As for it's utility in the 'Stans . . . well, that will be interesting. Not alot of roads like that, there.

With so much else to watch for . . . roaming livestock (horses, yaks, bactrian camels, goats, etc), road conditions, the ever vigiliant revenue generation officals (aka 'police'), scenic views and signage in cyrillic . . . at least in UZ, it's a lot more critical to SEE a fuel station WITH fuel than optimize on your current usage !
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  #18  
Old 1 Oct 2012
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Higher 5th gear for airhead gearbox

Hi,
I fitted a 5th gear to my R100GS PD output shaft back in December 2007 that gave a 6% higher ratio. Since then the bike has done 100,000 miles (340,000 miles in all) and it continues to function well. It is a simple and straightforward swap once you have dismantled the gearbox.
The gear (part number: 23221242992z) was supplied by S Meyer BMW; S.Meyer GmbH (limited company) - BMW motorcycle spare parts - Homepage
Meyer's in those days also listed a pair of gears, one for the lay-cluster and one for the output shaft that would give a 10% higher ratio. I fitted the 6% one because at the time they only had that in stock and I couldnt wait.
Airhead gearboxes are quite easy to work on, but it is important to remember to get the endfloat on the three shafts shimmed correctly, so as to ensure longevity. Also bear in mind it is worth checking to see if the outputshaft bearing at the clutch end has provision for a circlip to retain the bearing (BMW went through a phase of manufacturing some shafts without a circlip groove, which can cause premature bearing wear). If it dosen't then (as was the case with my shaft) you should make provision for a circlip on the shaft.
Regards to all
Guy
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  #19  
Old 2 Oct 2012
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Quote:
Originally Posted by plainshorse View Post
....
Also bear in mind it is worth checking to see if the outputshaft bearing at the clutch end has provision for a circlip to retain the bearing (BMW went through a phase of manufacturing some shafts without a circlip groove, which can cause premature bearing wear). If it dosen't then (as was the case with my shaft) you should make provision for a circlip on the shaft.
Regards to all
Guy
Yep, that was the reason for my gearbox repairs after only 18 kkms The '93 models had no circlip fitted.

Since then I have done over 120 kkms without any problems.
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