Reply To: Norton Big 4 Spark Plugs

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What you need to do is to take the sprocket off the magneto. You will find that the nut is a left hand thread (I think) and the shaft is tapered with no keyway. Do not try to lever the sprocket from behind because you will b******r the bearings in the mag, the only way to do it is to pull it off with a puller, pushing on the end of the shaft.
Once the sprocket is loose on the shaft you will find that you can turn the engine without the rotor in the mag moving- set the engine at 3/8″ BTDC, then turn the mag in the direction it normally runs in and stop when the points are just opening. Replace the sprocket and timing chain on the magneto shaft and with a small socket give the sprocket a sharp tap to seat the sprocket on the shaft taper. The engine is now timed accurately.