AJS Ignition timing

[Guy Wilson]

The mag timing on my AJS 350 is 39 or 41 respectively ( I have a competition mag on the bike ) degrees BTDC fully advanced... my question may be a daft one... the Mag drive sprocket from the engine turns twice for one rotation of the crankshaft..is that correct? If so, should I back the sprocket up double the degree setting from TDC to either 78 or 82 degrees? Logic says yes...but. logic has stopped many things in the past..
Thank you!
Guy

[Guy Wilson]

39 degrees advance is 1/2 an inch back down the barrel from TDC for the piston.. I'll try that and see how far back the mag sprocket rotates..
Guy

[RDfella]

the Mag drive sprocket from the engine turns twice for one rotation of the crankshaft..is that correct?

No. The drive sprocket turns twice for one turn of the mag. ie the mag turns 1/2 the speed of the crankshaft.

[Rex]

A big old single like doesn't need Japanese accuracy where the timing is concerned, so 39 or 41 would both be near enough, and if you have manual timing then you can adjust to the sweet spot as you ride.
A competition mag is usually no more than a red label after this amount of years have passed.

[Guy Wilson]

Thank you Rex, RD! that makes more sense,
Guy