350 Lightweight gearbox

[Roderick]

Is the 350 Lightweight gearbox the same as the 250 Lightweight or what are the differences?
Roderick

[greasemonkey62]

acording to my Roy Bacon restoration book the model 14 250cc was 21 tooth engine sprocket, 50 clutch, 19 gearbox final drive and 55 rear wheel.
the model 8 350cc was different at 22 engine/ 46 clutch, 18 gearbox final drive and 55 rear wheel.
The lightweight gearbox internal ratios are quoted as for the years they are in production with no variation quoted between the 350 and 250 internals so I think its safe to say the final gearing is adjusted with the four drive sprockets between the 350cc and 250cc bikes and the gearbox internals are the same for both models.
Cheers Ray.

[BigAl350]

Ray is absolutely correct as far as I know. However, I believe that the 250cc boxes have a slightly different serial number - the 350cc boxes may start with "G". I'm away from my home PC at present so will check later.

Al

[ajscomboman]

Here we go.

Early 250's used a single row chain simplex clutch later CSR's used the duplex chain which required a longer mainshaft. To confuse the matter even more two types of cluch centre were used requiring two diferent mainshafts. In total 4 mainshafts and 2 centres over the production years were made. The internals are pretty much interchangable with ratio changes for the scrambler. Then we get onto clutch baskets etc etc. A minefield but all good fun .

[John Jarrett]

I think that you will find that the mainshaft at the clutch end is different for a 350 versus a 250. Not sure why, but the illustrations of the 4 different mainshafts (2 for each 250 and 350) are in the workshop manual.

[Tolly]

Rob is spot on here, excluding the CRS 250, the difference is mainly in the length of the main shaft. But as you can see from Rob's answer it is not straight forward.

[Roderick]

Thanks to everyone who replied. Very helpful. Thanks again. Roderick