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 :D

Hans

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 !

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

Yep, that was the reason for my gearbox repairs after only 18 kkms :cursing: The '93 models had no circlip fitted.

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

High 5th Gear
 

Did you ever fit the tall 5th Mark? If so how did it fare, did the 800 manage to pull it?

"tall" is somewhat exaggerated :cool4: The revvs drop by about 500 rpm which saves a bit of fuel. Power-wise no probs, but when about to overtake fast moving traffic I have to change to 4th gear ;o)

Now the R80 isn't exactly a racing machine, but with the shorter 1st and longer 5th I'm happy. When the pistons are worn down I'll fit 1040cc, which I found a couple of months ago. Then it might make sense to fit the rear drive of the R100without changing the gearbox.

Not yet, I thought at 100,000 miles my gearbox would need an overhaul but it was fine, I thought the same at 150,000 when I asked this question, it has now done 170,000 and still seems fine so as it isn't broken I won't fix it.
As for the higher gear my monolever G/S has higher gearing at the bevelbox which it pulls no problem so I am expecting the paralever GS to do the same even if it is a little heavier.