Donor Gearboxes

[F5 Dave]

The NSR carbs are small and big at the same time. Honda do thier double cable thing and it can take quite a bit of awkward real estate.

[husaberg]

The Yz is case reed, handily. My mate has some nsr250 carbs which are arranged in pairs that I can pinch, hopefully I can find another set as two little banks will be nicer than 4 individual carbs. I’ll have to offset the reeds or inlet manifolds slightly to get them right so the carbs aren’t stacked above one another.

But first I’ll do an accurate model of the gearbox, I’ll try use my mill like a CMM and confirm what I’ve found with digital callipers.

Yamaha did this with the YZR500 V4 ow..?whatever it was in 98


Honda mounted the reeds side on with the NSR250.

And you of course know this as you mentioned you have a RGV.

The NSR carbs are small and big at the same time. Honda do thier double cable thing and it can take quite a bit of awkward real estate.

They start at 24mm for the MVX250 and go to 28 i think for the NS and up to a nominal 32-34mm i think for some of the NSR250's


they are nicely made carbs but yes use a bit of realestate but height not width. As you say.
the old GT380 first ones had a linkage that could adapt to a std VM i think. okay no
but they would be about the right size..



but TZ750s just had cable splitters....

https://www.worthpoint.com/worthoped...bly-1787831373

[Grumph]

The NSR carbs are awkwardly laid out as they come. Lot of real estate on the left taken up by the cable drum etc, then the fuel feed is on the right.
The set i adapted for the bucket, I drilled and tapped the fuel gallery for an entry on the left under the cables and plugged the right hand end.
On the bucket the rhs was hard up against the frame. It's probably possible to make one set with everything on the right if you need them to be mirror image.

[F5 Dave]

MC18s are 28mm and I think they stayed pretty small.

[el chupacabra]

So my height gauge has showed up and I have since put it to good use, getting the engine measured up and drafted little by little. The gearbox does appear to be on the heavy side around 6.5kg.

[el chupacabra]

Quick Update, I'm starting the design by drafting up a cassette gearbox, here's a couple of hours work, obviously I'll be able to print this and refine it. I've yet to add the shift fork guides and other minor features.

Here's an RGV cassette for comparison. This one is a whole lot heavier and it seems a whole lot harder to incorporate into a cassette style gearbox.

[F5 Dave]

RGV gearbox die with 50hp so maybe bigger is useful for reliability.

[husaberg]

Quick Update, I'm starting the design by drafting up a cassette gearbox, here's a couple of hours work, obviously I'll be able to print this and refine it. I've yet to add the shift fork guides and other minor features.

Here's an RGV cassette for comparison. This one is a whole lot heavier and it seems a whole lot harder to incorporate into a cassette style gearbox.

Cassetes are cool and all but wouldn't horizonal split be easier and provide most of the benefits?
From memory the britten lower case was basically a sump, flip it up and whip it off..... a lot like a VT250 actually...
i assume that's what the trumpy was going off the bearing....

[el chupacabra]

Horizontal split isn’t off the cards, although I think a 3 piece crankcase might get complicated with the twin cranks and a lay shaft, I was just trying to emulate what everyone else does with twin crank bikes seeing as it works.

Hmmmm soo many decisions.

[husaberg]

first 3 Cagiva last 3 RGV late.


https://www.kiwibiker.co.nz/forums/a...p?albumid=4842

https://www.kiwibiker.co.nz/forums/a...p?albumid=4848

https://www.kiwibiker.co.nz/forums/a...p?albumid=4861

https://www.kiwibiker.co.nz/forums/a...p?albumid=4845

https://www.kiwibiker.co.nz/forums/a...p?albumid=5064

https://www.kiwibiker.co.nz/forums/a...p?albumid=4837

https://www.kiwibiker.co.nz/forums/a...p?albumid=5017

[el chupacabra]

Thanks for that, that’s an awesome amount of reference material.
I think the cassette is the way to go at the moment. It seems like a common theme.

[husaberg]

Thanks for that, that’s an awesome amount of reference material.
I think the cassette is the way to go at the moment. It seems like a common theme.

Well yes on a GP bike yes as they have about 8 ratios to choose from for each gear and a minimal time to change between practice sessions.
it was also no cost bared exercise
I am not 100% sure triumph has that many options....i think they did alter some ratios. second third maybe

[el chupacabra]

I’m not running a cassette to change the ratios, I’m more concerned with ease of manufacture and ease of assembly. Although it’s a bonus if I kinda commercialise it in the future. I also don’t want to make the cases out of too many pieces as I’m sure that won’t make them any stronger and possibly harder to machine.

Also I can print and test my cassette relatively easily which is also nice before carrying on with the rest of the design.

But if someone were to show me a design that makes my design simpler, I’ll be all over it. I could do horizontally split but I’m not 100% sure how I’d lay it out as the layshaft might make it real long.

[husaberg]

I’m not running a cassette to change the ratios, I’m more concerned with ease of manufacture and ease of assembly. Although it’s a bonus if I kinda commercialise it in the future. I also don’t want to make the cases out of too many pieces as I’m sure that won’t make them any stronger and possibly harder to machine.

Also I can print and test my cassette relatively easily which is also nice before carrying on with the rest of the design.

But if someone were to show me a design that makes my design simpler, I’ll be all over it. I could do horizontally split but I’m not 100% sure how I’d lay it out as the layshaft might make it real long.

That's why i like single crank, as by brain is to small.... It also makes it shorter by making it wider. gives more room for intakes as the cylinders are opposing It also cuts down on the gubbins needed. What are your plans for the ignition?

[el chupacabra]

Just running a zeeltronic 4 channel unit with two pickups off the standard 85cc flywheel. Nothing fancy.
The only reason for the 4 cranks is to do away with a custom crank. I can see that being an expensive exercise especially for a high wear item when it’s 85cc and you want to be revving the nuts off it all the time.