Donor Gearboxes

[husaberg]

I’ll spin them in the same direction and fire them in pairs 90* apart. I’m pretty sure the RG500 spins in the same direction.

Attachment 352348

i would have said no but it looks as if they do

[F5 Dave]

I’ll spin them in the same direction and fire them in pairs 90* apart. I’m pretty sure the RG500 spins in the same direction.

Attachment 352348

So from this picture there's a layshaft with primary gear visible behind the carb driving the clutch it looks like. . . On my phone screen in the sun on the deck ..

[el chupacabra]

Yeah, that’s the plan, have the layshaft drive the clutch exactly like the RG500 although all of the gears will be straight cut. I don’t think the engine will be too long as the layshaft is almost between the cranks. It might be quite tall though, but 85cc cylinders aren’t particularly large.

[F5 Dave]

So your concern is multiple cranks and the coupling. Else the logical would be drive it off one crank end and counter rotate driving other crank direct. It is tempting but you are probably right if you don't have a custom crank designed to effectively transmit 4 cylinders power through one joint.

Not totally keen on backwards for both, but you'd be very unhappy if you created something that just broke at the weak spot every 2nd meeting. Life is a compromise. Lots of oil as Jimmy sez, and aim for completion.

[Grumph]

i've got a good broken-apart drawing of the RG500 with 4 separate cranks if it helps. From Vic Willoughby's Racing Motorcycles book. I can if needed photo it and post it here.

[el chupacabra]

i've got a good broken-apart drawing of the RG500 with 4 separate cranks if it helps. From Vic Willoughby's Racing Motorcycles book. I can if needed photo it and post it here.

That would be awesome, it’s always good to see how other people have done things.

[Grumph]

I apologise for the flash bounce. Can't turn it off on this camera.
If you're coming up for the CAMS meeting I could loan the book.

[husaberg]

There is some pics on robinsons book not sure where it is though......

[el chupacabra]

I would appreciate that but I am not going to any CAMS meeting, unless that's the same time as motofest as I may heading to that.

Tonight I took some rough measurements and pulled out the gearbox, it is a fairly substantial unit. Can anyone tell me what the split gear on the clutch is for?

[pete376403]

If the split gear is the same size as the one it backs on to, and if it is radially spring-loaded, then it is to reduce backlash/ clutch gear rattle

[el chupacabra]

Thanks, I was thinking it would be for something like that, I cant recall any other bikes I've worked on having something similar.

Jotting down some known dimensions to get a rough idea of size.

[husaberg]

Thanks, I was thinking it would be for something like that, I cant recall any other bikes I've worked on having something similar.

Jotting down some known dimensions to get a rough idea of size.

H100 and MB5 Honda's have them on the counter balancer shafts.

5 o'clock

if it was me i would use that extra space to push the top crank back widen the v out ...........But if it was me it would also never leave the drawing board....

[jato]

exciting progress here - once you've got a good set of drawings you are halfway there...the yz85's are case reed? or just the later models? it'd be interesting to overlay the reed valves and intake boots on to your drawings and see how the intake air path looks - 90 degree is good for balance but depending on the layout the intake air may have to turn quite a bit. we need to have a whip-around so you can work on it day and night...

[F5 Dave]

If anyone needs a givealittle page set up for projects, it's you. And Neil.

Hope the rain doesn't cause you any more drama up there.

[el chupacabra]

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.