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-   -   Higher 5th gear for airhead gearbox (http://www.horizonsunlimited.com/hubb/bmw-tech/higher-5th-gear-airhead-gearbox-66395)

mark manley 24 Sep 2012 08:26

Higher 5th gear for airhead gearbox
 
I am thinking about fitting a higher 5th gear in my R80GS, does anybody have experience of this, who makes them and anything to avoid when buying and fitting?

John Downs 24 Sep 2012 09:20

It has been years since I rebuilt my own transmissions on older airheads. So I was curious to see if Motobins was still in business and found this post:

Motobins parts quality - ADVrider

I am too cheap to pay for a higher 5th or lower 1st, and limited my rebuilding to new bearings and seals, shifter pawl springs and Kbike metal shifter roller wheel to replace the plastic one used in airheads. However reading the above post, I would use the Kaiser 5th with superior heat treating since it sounds like a superior part. Not sure I could bring myself to open up a perfectly good transmission just to replace 5th if there is nothing on the magnetic drain plug indicating imminent bearing failure though. But that's just me.

Labor is the main cost of rebuilding a transmission which is why I did the work myself and spent my money on parts. I ordered from Motobins and had good luck. It's not rocket science and there is plenty of useful information on the internet to aid the home mechanic.

Cheers,
John Downs

mark manley 24 Sep 2012 09:59

Thanks for that John, it sounds like the Kaiser is the gear to go for and I have no problem with paying extra for quality, has anybody fitted one of these and done a lot, as in 50,000 plus miles?
My dilemma is I am planning a trip across central Asia next year with a gearbox which is working fine but has done 160,000 miles without being touched. I know the rule if it ain't broke don't fix it but think it must be running on borrowed time now and rebuilding it at home will be easier than in the middle of Kazakhstan, alternatively I could just fit the gearbox from my G/S which has only done 40,000 miles since a rebuild.

John Downs 24 Sep 2012 15:39

Or just take the G/S and avoid high mileage GS trans and paralever potential problems. Not sure why you feel the need for higher 5th traveling through the Stans. Unless you have chronic airhead syndrome and love fettling. :-) I know I used to have it pretty bad. There is no cure.

But in all seriousness, 160K miles is very good for a paralever GS trans. I am a little jealous. I agree with you, better to rebuild at home with new bearings and seals and higher 5th. I was able to borrow trans tools from mates. Mainly flange puller and measuring plate for determining bearing shims. I have more time than money and like puzzles so it was satisfying work.

Cheers,
John Downs

mark manley 24 Sep 2012 16:41

Quote:

Originally Posted by John Downs (Post 393727)
Or just take the G/S and avoid high mileage GS trans and paralever potential problems. Not sure why you feel the need for higher 5th traveling through the Stans. Unless you have chronic airhead syndrome and love fettling. :-) I know I used to have it pretty bad. There is no cure.

I have used both for travelling and prefer the GS with its longer, more comfortable seat and better front end. The G/S is even higher mileage and needs money spent on it before embarking on a longer trip with it.

Your diagnosis is correct with the syndrome and it is not just for the Stans but for everyday use I would prefer slightly higher gearing for more relaxed cruising and a couple more mpg.

John Downs 24 Sep 2012 17:10

Okay then. I never like to sink money into a high mileage bike I am taking on a long journey other than the usual tires, battery, tune up, grease bearings, new clutch cable and throttle cables that sort of thing. I would probably put the G/S trans in and spend my money on gas and kebabs. Rebuild the GS trans with taller 5th if you make it back without getting run over by a crazy Kazak. But that's just me.

Please note: justifying spending big bucks on higher 5th for a GS to get better fuel mileage and slightly higher cruising speed is a sign you have the chronic syndrome in it's advanced stages. There is no hope for you my friend. Just kidding.

Safe travels.

Kindest regards,
John Downs

oldbmw 25 Sep 2012 00:12

I lowered the gearing on my Enfield, the PO had fitted a 19 tooth sprocket in place of the original 18. It felt like I was going uphill all the time and I spent a lot of time changing gear and in fourth. when I fitted the 18 tooth sprocket the bike was much more tractable and will now accelerate ( within reason) up inclines whereas before it always involved a gear change. better than that I now make faster times over the ground and the MPG remained at 95. So unless you spend a lot of time on motorways think carefully before raising the gearing.

Magnon 25 Sep 2012 07:43

Quote:

Originally Posted by oldbmw (Post 393790)
I lowered the gearing on my Enfield, the PO had fitted a 19 tooth sprocket in place of the original 18. It felt like I was going uphill all the time and I spent a lot of time changing gear and in fourth. when I fitted the 18 tooth sprocket the bike was much more tractable and will now accelerate ( within reason) up inclines whereas before it always involved a gear change. better than that I now make faster times over the ground and the MPG remained at 95. So unless you spend a lot of time on motorways think carefully before raising the gearing.

The airhead does have the advantage of one more gear which can be treated as a cruising gear and may not come into use at all when using back roads. Airheads are a bit thirsty and upping 5th gear for those longer stretches on good roads will certainly help the fuel economy.

I agree with the other point that taking a box apart just to fit the tall gear is perhaps tempting fate but then setting off with a box with with 160k on it is unlikely to end well.

Depending on how experienced you are with the GS gearbox (and if you have the special tools) I would either rebuild it and fit the higher gear or get it done professionally.

mark manley 25 Sep 2012 08:15

Quote:

Originally Posted by oldbmw (Post 393790)
I lowered the gearing on my Enfield, the PO had fitted a 19 tooth sprocket in place of the original 18. It felt like I was going uphill all the time and I spent a lot of time changing gear and in fourth. when I fitted the 18 tooth sprocket the bike was much more tractable and will now accelerate ( within reason) up inclines whereas before it always involved a gear change. better than that I now make faster times over the ground and the MPG remained at 95. So unless you spend a lot of time on motorways think carefully before raising the gearing.

The airhead GS is already lower geared than the G/S which is lower geared than the standard R80 so there is little risk of overgearing. In the end it might just come down to cost, I would prefer to spend my money on petrol and visas rather than parts for the bike and might just settle for a new set of bearings and seals, something I would do myself having rebuilt one in the past.

oldbmw 26 Sep 2012 00:34

Quote:

Originally Posted by Magnon (Post 393827)
The airhead does have the advantage of one more gear which can be treated as a cruising gear and may not come into use at all when using back roads. Airheads are a bit thirsty and upping 5th gear for those longer stretches on good roads will certainly help the fuel economy.

I agree with the other point that taking a box apart just to fit the tall gear is perhaps tempting fate but then setting off with a box with with 160k on it is unlikely to end well.

Depending on how experienced you are with the GS gearbox (and if you have the special tools) I would either rebuild it and fit the higher gear or get it done professionally.

My Enfield has five gears same as my old bmw.

Magnon 26 Sep 2012 07:32

Quote:

Originally Posted by oldbmw (Post 393958)
My Enfield has five gears same as my old bmw.

There you go, what do I know and I should have read your comment properly.

That said, neither my R80G/S or R100GS are overgeared in 5th but I can only guess at how they would pull a higher gear. The 80 might struggle at motorway speed into a headwind.

oldbmw 26 Sep 2012 23:49

Quote:

Originally Posted by Magnon (Post 393991)
There you go, what do I know and I should have read your comment properly.

That said, neither my R80G/S or R100GS are overgeared in 5th but I can only guess at how they would pull a higher gear. The 80 might struggle at motorway speed into a headwind.

I know it is not what you might first expect, but despite the Enfields cruising speed being reduced by 3% with one tooth less. I make significantly faster times over the ground. Partly because it will climb slopes easily now and forge against headwinds without the need for gear changing. It has not reduced my MPG at all. After all mpg is mostly a result of cylinder pressure versus the gearing and resistance. If you raise the gearing you will need to raise the throttle openings.
However the BMW motor I had changed mpg significantly with throttle openings and revs. for instance twice when I managed well in excess of 57mpg, once was following a friend on a diesel Enfield, the other was poodling about all day in the pyrenean mountains ( a surprise) because of being on the over run coming down the mountains.
normally it hovered around 50mpg. The Enfield does over 95 :)

Magnon 27 Sep 2012 17:18

I agree that upping 5th gear on an unfaired 80 could result in worse fuel consumption due to larger throttle openings required to maintain crusing speed into headwinds or incline.

I think it would be an improvement on a 100 which has a much flatter torque spread - you don't have to rev the nuts off it to make progress!

oldbmw 28 Sep 2012 00:06

My bmw was a 1985 R80RT.

bike was ok, but not for me. just too awkward, too heavy and too tall. and the gearchange was on the wrong side :)

Motorallyrider 29 Sep 2012 23:29

I have a higher 5th and lower 1st fitted to my R100GS & R100GSPD, both very useful, widely available from most aftermarket BMW parts dealers. Had both boxes rebuilt at the time of fitting.


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