Close Ratio Gears

Has anyone ever converted a 6 speed crossover box to Triumph / Norton format - input and output on the LHS ?

Kvinnhering said:

Bernhard said:

acotrel said:

Thanks for your help with this. Apparently my friend has been able to source the gears he needs from the info you have provided.

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Bernhard.
I'm curious how it goes with your improved (stronger) first gear? Have you tested any gears?

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Not sure I am interpreting your message correctly, how do you mean STRONGER first gear?
As far as I am aware all the gears listed for the Norton gearbox , as available over the counter, the semi close ratio gears I used closed up the 2,3,4 ratios whilst maintaining a standard first gear.

lcrken said:

Like pommie john said, I don't think there are any close ratio 4-speed sets that let you keep the original 2.56 first gear ratio. Some of them keep the stock 14/28 first gear pair, but they also change the fourth gear pair (sleeve gear and countershaft gear) from the stock 23/18 to either 23/19 or 22/20, which raises the first gear ratio to 2.18 or 2.2, resp. The closest currently available kit to what you are looking for is probably the RGM close ratio gearbox set with kick start for AMC boxes,

http://www.rgmnorton.co.uk/buy/close-ra ... ox_559.htm

which gives you closer second and third spreads, and a 2.05 first gear ratio.

The Norvil Production Racer 4-speed had a 2.18 first gear ratio, and the 5-star or Barton set had a 2.2 first gear ratio, but they haven't been in production for a long time now, so you'd have to find a good used set. Good luck with that!
I previously posted a table of all the 4-speed combos I know about here

close-ratio-commando-transmission-t22319.html?hilit=gearbox ratios
Ken

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There e was a Scarborough gearbox ;

what-scarborough-gearbox-t12340.html?hilit=scarbourgh%20gear%20box%20Scarborough%20gearbox#p211755

The 'Scarborough' bottom gear as so called in the UK was a modification of the bottom gear ratio to make negotiating the hairpin turn at the Scarborough (Oliver's Mount) circuit easier and quicker, this particular turn having a steep downhill approach, a very abrupt turn followed by an equally steep uphill exit. Despite the specially lowered bottom gear, serious clutch abuse was also required to make a fast and competitive exit.

The mod involved the replacing of the bottom gear pinion that meshes with the standard layshaft integral gear, and the pinion was made by cutting one extra tooth on the standard gears PCD. The meshing of the gears was not strictly correct, but despite this the modification proved satisfactory and any serious minded racer intending to do well at the circuit would have changed his bottom gear ratio thuswise.

Of course this was back in the days before Schaffleitner or Aagaard conversions to 5 and 6 speeds became available

Just an idea ....
Hit a few auto jumbles and find a few good condition AMC/Norton 24 /18 t 4th gears. Chomp the sleeve off of one 24 t gear and put 4 slots in it and hey presto a 24 t first gear. The corresponding 18 t gear requires a small splined spacer and I sliced up an old worn 18 t gear to supply it. For seconds and thirds the AMC/Norton 20/22 - 22/20 pairs are perfect, the 3rds are easily available and there are still a few new old stock 2nds around if you know where to look. Thus you end up with gears 18-20-22-24 teeth one way and 24-22-20-18 the other giving a nice set of ratios with, if memory is correct, around 1200 rpm drop between gears and a reasonably low gear to get you off the line faster than most......worked perfectly in our old Atlas decades ago and one did not waste time changing gear so much....

The weak link in production Norton twins is obviously the gearbox. For my own bike, I chucked the 4 speed close ratio AMC box and bought a 6 speed TTI. My friend is one of those guys who has a sick wife and not much money. I don't believe there is a cheap way to make a decent road racing gearbox out of an AMC box. When I was using the 4 speed box, I always did it with fear and trepidation. The torque delivered by a commando engine can be massive, and fanging it during a clutch start is just asking for trouble.