19S engine sprocket size

I have a 1956 19S which was puling a sidecar. I am now running it solo. It presently has a 19 tooth gearbox sprocket and a 19 tooth engine sprocket. Should I change to a 20 or 21 tooth engine sprocket? Does anyone have any suggestions?

Hi Michael,

The '54-'58 model 19s would have had a  21 tooth engine sprocket, 4.52 overall gearing, and a 43 tooth rear sprocket as a solo machine. I think there were 2 or 3  different offsets on the engine sprocket, so be sure to get a new one with the same offset as the one you have now. Perhaps others can comment on what they are running?

I found it interesting that the model 19R (rigid) from '54-'55 used an 18 tooth engine sprocket, 5.28 overall gearing, 43 tooth rear sprocket. I wonder why?

Skip Brolund

Hi!

Norton's fitted a 19 tooth engine sprocket as standard, mostly because the bike was marketed as a sidecar tug rather than as a solo machine. A 21 tooth engine sprocket could be fitted for solo use, all of the heavy weight singles and twins came with a 19 tooth gearbox and 43 tooth rear wheel sprockets, gearing changes were done by swapping the engine sprockets accordingly. Skip is correct about the sprocket offsets, there are about three different ones encountered, why? I'm not sure. RGM carry a full range of engine sprocket sizes and offsets for our old thumpers.

As for me and my 1958 19S, I run a 20 tooth engine sprocket and a 21 tooth gearbox sprocket, (I really needed a new gearbox sprocket and that was in stock.) the over all gearing in top is 4.30:1. The big single just lollops along at 60 per all day, seemingly without effort.

The engine is running an 84mm vincent piston, giving it 626cc and about 7.0:1 compression, this breathes through a 30mm AMAL concentric. Yes, the bike has a commando TLS front brake too.

I'm not surprised at the gearing choice for the 19R, it had to have been a real grunt monster for the heaviest sidecars available. Those big flywheels and that 596cc cylinder spell TORQUE!

Regards,

Albert

AAAHHHHH, that does make sense! Thanks Albert!

Skip

Previously wrote:

I have a 1956 19S which was puling a sidecar. I am now running it solo. It presently has a 19 tooth gearbox sprocket and a 19 tooth engine sprocket. Should I change to a 20 or 21 tooth engine sprocket? Does anyone have any suggestions?