Calling All Gearbox Gurus . . . .

[Voyager]

You may recall that 'Seancb' was stuck in France with a bust gearbox.

Well, he is mobile again and his gearbox is in bits on my workbench.

There's not a lot wrong with it; just a broken spring and a worn front output shaft bearing. All the gear clusters are in good order.

I am going to re-build the box with a full set of new bearings, springs and seals, then one day we'll swap it back.

However . . .

Sean would like a longer fifth gear. I thought about changing the bevel box ratio but that would raise the gearing across the board.

Is there anyone out there who does alternate 5th gear and lay shaft conversions for a R100GS Paralever gearbox ?

Now you're going to ask me to count teeth are'nt you

Thanks on advance.

Bob.

 

[nick.ct]

Got one fitted in mine, was there when I bought it. I think it came as a kit from a company in Germany, dont have the details with me at the moment. It seems to be lasting OK, several trips round Europe since and its been fine.

Nick

 

[John Armstrong]

Have a look here: http://www.hpn.de/english/english.html

Select "engine & gearbox" onn the right side and click on "go" and then about half way down ....

 

[Rob Farmer]

Siebenrock - http://www.siebenrock.com/index1.php?sprache=en

or

Motoren Israel http://www.motoren-israel.com/produ...nrad-langer-5--Gang-mit-X-ab-Bj--04-1982.html

 

[Sean Kelly]

Kept my 800 bevel and Andrew Sexton fitted a taller 5th gear, the setup works well.

Cheers

Sean

 

[Voyager]

Thanks guys, I knew I could rely on you.

Food for thought there.

I'll see what Sean wants me to do

Bob.

 

[seancb]

Hi
all

just checking that if i got the taller 5th gear from siebenrock would it work on the standard shafts?
Sean

 

[Voyager]

Hi
all

just checking that if i got the taller 5th gear from siebenrock would it work on the standard shafts?
Sean

Yes,

No other changes. Just buy the output and intermediate shaft gears and I'll fit them.

Bob.

 

[Rob Farmer]

You shouldn't need the intermediate gear, just the output shaft "longer fifth" The intermediate gear is for fitting the later (17.5°) tall fifth gear to the very early 80's box that came with 15° gears - it's to save having to buy the whole layshaft thats been the only option until recently

Just buy the tall fifth gear that's sold as being marked with an X if it's for a Paralever

 

[Sylvester]

Does the taller 5th gear make a big difference? does it leave a big gap between 4th and 5th, whats the rpm drop between the two?

 

[Voyager]

You shouldn't need the intermediate gear, just the output shaft "longer fifth" The intermediate gear is for fitting the later (17.5°) tall fifth gear to the very early 80's box that came with 15° gears - it's to save having to buy the whole layshaft thats been the only option until recently

Just buy the tall fifth gear that's sold as being marked with an X if it's for a Paralever

Eh !

How does changing one gear affect the ratio ?

I'd have thought that the pair have to be changed - larger intermediate and smaller output gear to raise the gearing.

The shaft centres aren't changing so how do you fit less teeth on one gear and still keep them in mesh ?


Now I'm really confused

Explanation please - before I head up any more garden paths.


Bob.

 

[Voyager]

Does the taller 5th gear make a big difference? does it leave a big gap between 4th and 5th, whats the rpm drop between the two?

The sites selling the conversion quote 5% or 6% reduction (in output shaft revolutions).

I don't know what that feels like on the road.

Bob.

 

[Garry H]

Whats wrong with the standard gearing
Seems fine to me

 

[seancb]

calling Rob Farmer

Hi
can I check with the the taller 5th it works on the standard shafts and it only the new gear you need.
just need to check this thanks
Sean

 

[Steptoe]

I've always fitted a 1st and fifth together - but it's been at least 15 years since i last did it on an airhead, so i may be spouting bollox.

And it used to shorten the life of the bearings

 

[Rob Farmer]

Voyager,

The intermediate gear is an easy way to change the earlier 15 degree gearboxes to 17.5 degree components. Until recently you had to replace the entire layshaft to convert to 17 degrees.

I'm with Garry on this. Can't see any problem with the standard gears unless you have tuned the motor. 800's with Siebenrock kits will rev out in top gear. The taller 5th gear helps.

Neil,

1st and 5th are miles apart. I don't think anybody sells the shorter first anymore

 

[Rob Farmer]

Hi
can I check with the the taller 5th it works on the standard shafts and it only the new gear you need.
just need to check this thanks
Sean

Sean,

It's just the taller 5th gear you need and it fits on the standard shaft.

 

[seancb]

thanks I have sorted out buy the 5th gear to day thanks for sorting out the confusion about the gear Sean

 

[Voyager]

Voyager,

The intermediate gear is an easy way to change the earlier 15 degree gearboxes to 17.5 degree components. Until recently you had to replace the entire layshaft to convert to 17 degrees.

I'm with Garry on this. Can't see any problem with the standard gears unless you have tuned the motor. 800's with Siebenrock kits will rev out in top gear. The taller 5th gear helps.

Neil,

1st and 5th are miles apart. I don't think anybody sells the shorter first anymore

Rob,

HPN sell the shorter first gear as well as the taller fifth gear - see here:

http://www.hpn.de/english/english.html

They also mention the need to change the input shaft gear when converting earlier gearboxes to 17.5 degree tooth form.


I'm still confused though.

I originally assumed that to change the 5th gear gearing would require a smaller Output shaft gear, plus a larger Layshaft gear. I was forgetting that the layshaft gear is only an idler for 5th, fitting a larger one would also lower the ratios on the four lower gears .

I don't see how the ratio can be altered by changing just one gear - unless there is some cunning way of meshing fewer teeth without reducing the overall diameter.
For 5th gear the ratio is the relationship between the No of teeth on the input shaft and the No of teeth on the output shaft, the Layshaft plays no part (apart from transferring the drive from one to the other - its size doesn't matter).

Does anyone know how this conversion works in practice ?

No doubt all will become clear when Sean provides me with the new output shaft gear to fit

You live and learn (hopefully).

At least its cheaper and easier to install than we first thought.

Bob.

 

[Rob Farmer]

The size of the layshaft gear does matter when it's driving fifth gear, the rest of the time it's just used to rotate whichever gear is selected. When it's being driven in that manner only it's relationship to the input shaft gear matters.

I haven't counted the number of teeth on the taller fifth but would expect a tooth less and gears cut to accommodate the different size.

I didn't realise HPN had the lower first gear. That may be worth trying on my Mono.