Grosvenor 61
Registered user
Anyone tried fitting the hi-ratio 5th gear for touring? I'd be interested to know what the effects are, particularly with regard to fuel economy (R100GS).
Hi-ratio 5th gear modification
- Thread starter Grosvenor 61
- Start date
Thats an interesting post. I had planned to do this to an R80ST if the g/box needed a rebuild at any time.
I have fitted one, its easy enough to do if you're used to taking these boxes apart.
However, it was for someone else, so I can't give a first-hand account of the result. From what I heard he was pleased with the result (R100GS).
Bob.
However, it was for someone else, so I can't give a first-hand account of the result. From what I heard he was pleased with the result (R100GS).
Bob.
I'm going to put one in the Caff Racer, gearbox is the next job when I've re-assembled the bevel drive. That was stripped for inspection, seals and painting. 72k and it was fine, but I'll be surprised if the gearbox is as good, although it works fine!
the one bob fitted
it has dropped the re,s down so it wont rev the hell out of the bike at 70. but i think my g,box my have been lowerd by the last owner. As i can pull off in 2rd with out any prolems what so ever. and when i pull of in 1st i am straight in to 2rd still at very low rev,s
Grosvenor 61
Registered user
Hi-ratio 5th gear
Thanks for the replies - I think 'the one bob fitted' answers my question.
My gearbox is standard and although it is possible to pull away in second I do need to raise the revs a fair bit to avoid stalling.
The reason for my original query is that I find 4th & 5th are quite close together. As 5th is never used on B-roads or uneven terrain it seemed logical to persue the idea of raising 5th for A-road work.
I see that Moorespeed in Northampton offer a 10% higher ratio 5th gear (the Motobins standard one is 5%) - though this may be for use with their high compression pistons - will investigate.
I have seen reports suggesting that the improvement in fuel economy with a hi-ratio 5th is significant. As my bumblebee averages 40mpg (no, I don't abuse her) I'd like to try and improve this figure on longer runs.
Thanks for the replies - I think 'the one bob fitted' answers my question.
My gearbox is standard and although it is possible to pull away in second I do need to raise the revs a fair bit to avoid stalling.
The reason for my original query is that I find 4th & 5th are quite close together. As 5th is never used on B-roads or uneven terrain it seemed logical to persue the idea of raising 5th for A-road work.
I see that Moorespeed in Northampton offer a 10% higher ratio 5th gear (the Motobins standard one is 5%) - though this may be for use with their high compression pistons - will investigate.
I have seen reports suggesting that the improvement in fuel economy with a hi-ratio 5th is significant. As my bumblebee averages 40mpg (no, I don't abuse her) I'd like to try and improve this figure on longer runs.
for my bike i just sit in 5th on the main road ect and i be doing about 65ish at low ish revs can remmber off hand what the revs are but its not to bad
before i did the mode i would have to rev the hell out of it at 70mhp and it did not sound good. but after the mode it will hit 80iish before it sounds bad
Beemerboff
Registered user
The PO of my G/S had the box "professionally" rebuilt , including a higher fifth and a lower first. Cost him more than a replacement box.
Unfortunately the "professional" also used C1 bearings throughout, so the box now requires a major rebuild, and it has been replaced with a cheap second hand box with stock ratios while I source the parts for the rebuild.
If I didnt already know I wouldnt have noticed the difference, and after a week I dont - 200 revs isnt noticeable on a smooth running motor.
I havent noticed any difference in fuel consumption either, but from a gearing viewpoint that wont be any more than 1% anyway.
If you already plan on stripping the box I would go for +10% one , but IMHOstripping a good box to fit one would probably be the least bang for your buck you will get on an Airhead.
However if you have an old rattler which sounds like it is going to explode ar 4000 revs you may get more from it than me.
Unfortunately the "professional" also used C1 bearings throughout, so the box now requires a major rebuild, and it has been replaced with a cheap second hand box with stock ratios while I source the parts for the rebuild.
If I didnt already know I wouldnt have noticed the difference, and after a week I dont - 200 revs isnt noticeable on a smooth running motor.
I havent noticed any difference in fuel consumption either, but from a gearing viewpoint that wont be any more than 1% anyway.
If you already plan on stripping the box I would go for +10% one , but IMHOstripping a good box to fit one would probably be the least bang for your buck you will get on an Airhead.
However if you have an old rattler which sounds like it is going to explode ar 4000 revs you may get more from it than me.
I've rebuilt several gearboxes that have been exchange boxes through reputable outlets only to find they have badly worn gears and chinese C1 bearings. These are just a time bomb waiting to go off.
Theres somebody out there doing a lovely job of gearboxes though and I'd love to know who it is. Thunder asked me to check out his gearbox when he was rebuilding the bike for his africa trip. The gearbox had been rebuilt but we never did find out who by. Done a couple of others as well where we couldn't track down the mystery man. Always spot on with the correct bearings fitted. somewhere between the midlands and North of the country judging by where the bikes came from (it was never going to be from the south was it
)
Theres somebody out there doing a lovely job of gearboxes though and I'd love to know who it is. Thunder asked me to check out his gearbox when he was rebuilding the bike for his africa trip. The gearbox had been rebuilt but we never did find out who by. Done a couple of others as well where we couldn't track down the mystery man. Always spot on with the correct bearings fitted. somewhere between the midlands and North of the country judging by where the bikes came from (it was never going to be from the south was it )[/QUOTE]
could the mysyery man be Roger = the guy in a unit next to Tony Archer the upholsterer of fame - he is just aside the Galfarm stadium in Huddersfield I have met the bloke but not used his services ( I think he does wotoworks gearboxs for um
HTHY
)[/QUOTE]could the mysyery man be Roger = the guy in a unit next to Tony Archer the upholsterer of fame - he is just aside the Galfarm stadium in Huddersfield I have met the bloke but not used his services ( I think he does wotoworks gearboxs for um
HTHY
Somewhere between Bomber and Thunder having the desert storm bike somebody had the gearbox rebuilt, If anybody knows who did the work well have our man.
Some of the others want shooting.
Some of the others want shooting.
Grosvenor 61
Registered user
Thanks for the warning guys - it's not the first time I have heard horror stories about GS gearbox rebuilds.
As my stock box is in very good condition (less than 6000 miles) I think I will leave well alone, at least until a reliable specialist has been identified!
Don't know whether the mystery builder is Moorespeed - they're in Northampton, which is roughly the right area?
As my stock box is in very good condition (less than 6000 miles) I think I will leave well alone, at least until a reliable specialist has been identified!
Don't know whether the mystery builder is Moorespeed - they're in Northampton, which is roughly the right area?
Mr Scriminger perhaps - bit off to the East, but possible.
richie moore
Registered user
the gearbox man is not me, I only build gearboxs for people that do not complain about the price of the bearings, I only ever use SKF or FAG and a genuine input roller which is now £80 from BMW and a genuine input end of output shaft because it is a maximum capacity bearing that is a BMW part the normal c3 is not good enough and costs £30 and thats just 2 bearings, there is another 4 in there, you get what you pay for. the gearbox on my race sidecar has done 2 seasons with no problems and that now has 121 bhp going through it.
I'm pretty sure its not Richie or Steve Scriminger.
I'm not implying that anybody but the mystery gearbox rebuilder is doing a crap job but theres an awful lot of dodgy bearings and gears appearing in gearboxes that have been rebuilt fairly recently. I think theres an assumption being made that the bikes will not be covering many miles so its ok.
My favourite was one of the guys mates who was a fitter rebuilt his box for him. Nice cheap C1 chinese bearings and a gasket made out of a newspaper (to save a £1). The original shims were fitted adding loads of preload with the thinner newspaper gasket. The gearbox only lasted a few hundred miles before the bearings collapsed
Then theres the Irish fella who ran his freshly rebuilt gearbox for a few hundred miles with no oil at all in it
This was one of the well known gearbox gurus (who shall remain nameless) attempts. Charged a friend of mine £250 to upgrade the gear change mechanism on his R90 to the later spec but only actually changed one part of it. When the pair bound together (the old and new specs sit at different heights) and the bike wouldn't change gear without manually kicking the lever back my mate was told to stick with it as it needed to bed in. You can see the marks where it was catching and was never going to bed in. The same guru also charged him for -5% fifth gear but actually your stuck a standard 5th gear in.
I'm not implying that anybody but the mystery gearbox rebuilder is doing a crap job but theres an awful lot of dodgy bearings and gears appearing in gearboxes that have been rebuilt fairly recently. I think theres an assumption being made that the bikes will not be covering many miles so its ok.
My favourite was one of the guys mates who was a fitter rebuilt his box for him. Nice cheap C1 chinese bearings and a gasket made out of a newspaper (to save a £1). The original shims were fitted adding loads of preload with the thinner newspaper gasket. The gearbox only lasted a few hundred miles before the bearings collapsed
Then theres the Irish fella who ran his freshly rebuilt gearbox for a few hundred miles with no oil at all in it
This was one of the well known gearbox gurus (who shall remain nameless) attempts. Charged a friend of mine £250 to upgrade the gear change mechanism on his R90 to the later spec but only actually changed one part of it. When the pair bound together (the old and new specs sit at different heights) and the bike wouldn't change gear without manually kicking the lever back my mate was told to stick with it as it needed to bed in. You can see the marks where it was catching and was never going to bed in. The same guru also charged him for -5% fifth gear but actually your stuck a standard 5th gear in.
I hope i'm not on that list . . . I've not had any complaints about the few I've done for people.
Interesting comment about the 6403 C3 on the forward end of the output shaft. I've always used SKF C3s throughout, plus the special input roller from Motorworks/Motobins. Maybe I should change that practice and get a BMW bearing
.A full rebuild (all bearings, seals, springs & gasket) plus postage works out at about £195. I don't charge for my time as I only get 1 or 2 a year as a 'hobby job'.
Always learning, though.
Bob.
Doesnt Ogni know who rebuilt it?
Did Ogni sell it to Roger? I think Roger asked him and he didn't have it rebuilt.
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