1947 Model 18 Magneto driven sprockets

Hi Brian, can't help you with part numbers for that year but I would suggest that as a stocking filler you visit the National Motorcycle Museum website and order BMS reprints of the maintenance manual and parts list for your bike. I'm puzzled by your 15T/18T reference. The magneto has to run at the same speed as the inlet camshaft so both sprockets will have the same number of teeth. Wheel bearings might be due for replacement but first check the 3 studs holding the wheel to the brake drum, they may need to be tightened.

Cheers, Ian McD

 http://www.thehighsierra.org/PDFs/Norton46-49.pdf

Christmas cheers,

Mike

Hi Brian,

  Both sprockets are 15T, the camshaft sprocket is a flat surface with a Woodruf key-way whilst the magneto one has a deep recess and no key-way. The 1948 re-design used similar 16T sprockets, but you cannot use these on your engine. One thing to remember is that the magneto runs in a clockwise direction viewed from the sprocket end and the cable advance is the tight wire type.

   Don't worry too much about a gasket set as you can make your own with gasket quality paper. It is best not to use a head gasket, and to double grind the spigot joint. The top push-rod tube seal is a rubber one piece double hole part and is available, and the copper exhaust sealing ring is the same as a BSA Bantam D14 one.

   Years ago I had the same poblem as you with the back wheel and thought it was the bearing worn out, but when I stripped it out the bearing had partly seized and had worn the hub surface away. As an 18 year old this wasn't a big problem as I fixed it with Araldite !