Donor Gearboxes

[jato]

when previously recording the positions of the shafts/selector/guides and shift shaft on jap bikes so far there has been a pattern emerge - eg gsxr 1000 shaft centers 68.00mm shift guide to selector drum 34.00 centers - a bit of dummying up would confirm your calculations .

[husaberg]

What would be cool is a NSR250 box dry clutch option its also a cassette box.
it also gives the option to upgrade to NF5 RS250 gears later.
Pretty sure a guy did all the cad mapping one as well.

std they are wider spaced than a Triumph...
but dif years are different ratios
https://nsr-world.com/specs/nsr250/

[Grumph]

What would be cool is a NSR250 box dry clutch option its also a cassette box.
it also gives the option to upgrade to NS5 RS250 gears later.
Pretty sure a guy did all the cad mapping one as well.

IMO not a good option. RS250's seem to break 2nd gear on our circuits in NZ.

[el chupacabra]

I’m wondering now if that gsx600f will be fine other than the less than ideal jump from first to second. Seeing as it’s cheap and it’s a complete motor with carbs. The spacing between 3-4-5-6 looks pretty good, 2-3 maybe a 2,700 rpm drop from 13,000rpm. 1-2 is a big drop of around 4,000rpm

I do have an RGV VJ21 cassette sitting around with a munched 1st gear but I feel like all these old 250s are worth far to much to be pinching parts from and impossible to find spares for.

It’s a shame I don’t have the connections with people that will lend me parts so I can measure them over a few months or sell them to me cheap.

I definitely don’t want to be smashing gears.

[F5 Dave]

If it's a roadbike that will be fine. But it's not so it will be a Why didn't I start off with the right bits? Every time you try launch or in the hairpin.

[husaberg]

https://www.trademe.co.nz/a/motors/m...5?bof=6EikuEfh



Cramp used this series gearbox for project lionheart the homebuilt 500 v twin into a TZ250 frame.
he has the tool for the primary gears
ian.r.cramp@gmail.com as its a odd modulus
Is this what you were meaning with the separate cranks initially.

the bits i have start here and carry on.

https://www.kiwibiker.co.nz/forums/s...post1130295249

[jato]

I see a YZ 125 has a big reduction from crank to input shaft... so, knowing that as we speed up the primary drive ratio you transmit the same horspower but at a lower torque loading on the clutch and gears, if we were to change the ratio from the std YZ 125's 3.37:1 to say 2.25: 1 then we will be able to handle the torque peaks of two pairs of 85's no problem at all. with the inertia of 4 cranks(even though they are smaller than the std 125) the speed of the engine within its 360 degrees will be more constant than a single, which will also help being "kinder" than a single on the clutch and gears . Total clutch speed would be just over 5700 at 13000 engine revs which is a lot lower than a lot of clutches. A good cush drive in the back wheel as well as the std dampers in the basket would save any big shocks engaging gear. the little oil pump and a spray bar cast in would complete a light raceworthy set up . i expect the new primary drive gears needed would fit in with the need for a layshaft as per design. if you were worried about total heat soak into the clutch on a tight track you could easily fit a slightly bigger clutch such as a rmz 250 one (i have some under my bench you are very welcome to if needed).

[el chupacabra]

If it's a roadbike that will be fine. But it's not so it will be a Why didn't I start off with the right bits? Every time you try launch or in the hairpin.

You’re 100% correct, I should just take my time selecting the right bits. I do appreciate all the advice from everyone as well as I would have just jumped on the gsx gearbox without thinking about the spread.

I’ll keep my eye out for a 125mx bottom end or something 600 supersport related as they’re probably the only suitable ones. That triumph one might be ok, I’ll have another squizz over that today and look at the ratios.

I’ll also do a quick 3D model of the layout maybe tomorrow using some known dimensions and show you guys what I’m thinking as a picture paints 1000 words.

[husaberg]

You’re 100% correct, I should just take my time selecting the right bits. I do appreciate all the advice from everyone as well as I would have just jumped on the gsx gearbox without thinking about the spread.

I’ll keep my eye out for a 125mx bottom end or something 600 supersport related as they’re probably the only suitable ones. That triumph one might be ok, I’ll have another squizz over that today and look at the ratios.

I’ll also do a quick 3D model of the layout maybe tomorrow using some known dimensions and show you guys what I’m thinking as a picture paints 1000 words.

For what it's worth I went through all the common 600 and 400 stuff none of them are actually very close ratio. I could find anyway.
Even the VFR400's and CBR's
125mx gears are tiny compared to road stuff or the 2 stroke proddy stuff plus lots of late stuff were 5 speed.
If the trump or Ducati doesn't suit ,if it was me i would just use a VT250 they are decent size ,made for a narrow bike and were used on factory std bike up to 45 HP so might work at a pinch every wrecker in NZ a=is full of them and the gearbox's are not the reason why.
they have plenty of permeations and were used manual and hydraulic clutch and left and right actuation.

[el chupacabra]

I’ve had a google of the vtr gears and they look fairly narrow like the 125. I just remembered i do have an RG150 complete sitting in my mates lock up. . . I wonder if the gears with a new primary drive ratio will work. I did want to make a 125 gp chassis for it though but maybe it’s a worthy sacrifice.

[husaberg]

I’ve had a google of the vtr gears and they look fairly narrow like the 125. I just remembered i do have an RG150 complete sitting in my mates lock up. . . I wonder if the gears with a new primary drive ratio will work. I did want to make a 125 gp chassis for it though but maybe it’s a worthy sacrifice.

The VT gear are indeed narrow, but are a much larger dia gears than the 125's.
They run a large id Primary i am using the clutch on a design i will never complete.
the early f's and posily others are closer ratio.
all of them are of course smaller than a 250 proddy.

[el chupacabra]

I guess the vtr gears may also take more abuse with a dedicated gearbox oil and not sharing it with the engine.

[jato]

looks like the RG 150 1st gear would be ok following the cows... another option is if you found a gearbox with 5 of the 6 gears looking good then build a new one to the ratio you want 1st is often easy to build a new driven gear with a corrected profile to "match" the existing main shaft

[el chupacabra]

This doesn’t look outrageous from the triumph and it’s only $250 for the lot. With half of the crankcase included. Husa was probably onto a good thing from the start. Does anyone have any bad experiences with the triumph gearbox? Otherwise I think this looks like the best option.

[husaberg]

looks like the RG 150 1st gear would be ok following the cows... another option is if you found a gearbox with 5 of the 6 gears looking good then build a new one to the ratio you want 1st is often easy to build a new driven gear with a corrected profile to "match" the existing main shaft

if you wanted to do this this site https://novaracing.co.uk/
go to manufactures and the list options
make them as do other Asian sites but normally for little underbones