Rocker shafts

I was going through a box of stuff that came with a purchase of a bike I had bought. In it were some rocker shafts plane, scrolled and some with the machined in flat spot. (None in great shape) So I was wondering why Norton went away from the scrolled ones when they went to the 6 start pump? Was it just production cost or some other reason. I would have thought that you would get better lubrication with a scrolled shaft over a plane one. Were there year breaks when these changes came? No other reason than curiosity to my question.

John Ebert
Texas

John I think it is about the Norton head being over-oiled and the shafts changed to restrict oiling.

N0rt0nelectr@ said:

So I was wondering why Norton went away from the scrolled ones when they went to the 6 start pump?

Click to expand...

Prior to the factory fitting the six-start gear, doubling the speed of the pump (from 116372) the rockers were fed from the scavenge, so at reasonably low pressure.
From 116372 the rockers were fed from the feed side of the pump so at high pressure, thus the change from scrolled to plain rocker spindles (with flats) was necessary to prevent over-oiling of the valve gear (and loss of engine oil pressure). Fitting scrolled shafts or plain shafts with the flats facing inwards will cause serious over-oiling.

After all these years I am still learning about Nortons.
Thanks
John