GT40s.com - View Single Post - 6-speed UN1?

Howard Jones · 04-16-06, 05:18 PM

If I remember correctly the Renault way that the input shaft stub connected to the main shaft was left hand threads into a loosely pinned coller. This new six speed method looks like a splined shaft into a splined housing. Would this be better? I think so.

The pictures I've seen of broken UN1 input shafts all failed at the stress riser caused by the change in material diameter of the shaft itself. This was at a point right after the threads on the gearbox side of the shaft.

A similar sort of thing is at the same location on the "new" shaft right after the splines. The "new" shaft does looks the same diameter as the splines so maybe this isn't an issue as in the original Renault. This would be my bet of where a failure would occur if it did, never the less. I would have liked to see a one piece shaft. Now don't think I know enough about materials or gearbox design to have anything other than an opinion on this. I am only pointing out the little information I am aware of.

The fact is, the "new" stuff is nearly 30 years on in design, and taking into account for better materials and that the spline arrangement looks better than the threaded Renault method all may be well.

The other thing is the diameter of the shaft itself. I would assume that like other replacement/ upgrade shafts increasing the diameter would also make the "new" parts stronger as well.

Lastly I believe that straight cut gears are less stressful on the cases themselves than the original design. Straight cut gears have less of a tendency to force themselves apart under load. This produces less load on the bearings and their housings in the cases. The straight cut gears themselves do have higher stress loadings, stress risers at the gear face root, but can be accounted for in design.

The best part seams to be the full gear-set 1st-6th inside the cases with bearings on both ends and reverse hanging out back. This in itself would be worth the effort.

I think I agree with the idea that the location of the gears on the shaft in relation to the pinion gear being of the least important design points discussed here, although valid in concept.

I should say that I'm not trained in gearbox design. I have fixed a lot of bike gearboxes in my time thought so my opinion is worth what it cost.

Looks very interesting!

SO does anyone have a price? Gear ratios? Can a "kit" be bought?

04-16-06, 05:18 PM	#11 (permalink)
Howard Jones 10 tenths Join Date: Jun 2002 GT40: San Francisco Bay Area California USA Posts: 1,883 Rep Power: 25	Re: 6-speed UN1? If I remember correctly the Renault way that the input shaft stub connected to the main shaft was left hand threads into a loosely pinned coller. This new six speed method looks like a splined shaft into a splined housing. Would this be better? I think so. The pictures I've seen of broken UN1 input shafts all failed at the stress riser caused by the change in material diameter of the shaft itself. This was at a point right after the threads on the gearbox side of the shaft. A similar sort of thing is at the same location on the "new" shaft right after the splines. The "new" shaft does looks the same diameter as the splines so maybe this isn't an issue as in the original Renault. This would be my bet of where a failure would occur if it did, never the less. I would have liked to see a one piece shaft. Now don't think I know enough about materials or gearbox design to have anything other than an opinion on this. I am only pointing out the little information I am aware of. The fact is, the "new" stuff is nearly 30 years on in design, and taking into account for better materials and that the spline arrangement looks better than the threaded Renault method all may be well. The other thing is the diameter of the shaft itself. I would assume that like other replacement/ upgrade shafts increasing the diameter would also make the "new" parts stronger as well. Lastly I believe that straight cut gears are less stressful on the cases themselves than the original design. Straight cut gears have less of a tendency to force themselves apart under load. This produces less load on the bearings and their housings in the cases. The straight cut gears themselves do have higher stress loadings, stress risers at the gear face root, but can be accounted for in design. The best part seams to be the full gear-set 1st-6th inside the cases with bearings on both ends and reverse hanging out back. This in itself would be worth the effort. I think I agree with the idea that the location of the gears on the shaft in relation to the pinion gear being of the least important design points discussed here, although valid in concept. I should say that I'm not trained in gearbox design. I have fixed a lot of bike gearboxes in my time thought so my opinion is worth what it cost. Looks very interesting! SO does anyone have a price? Gear ratios? Can a "kit" be bought?