AJS & Matchless Owners Club

Good evening all, Has any one encountered a problem with Magneto timing slipping on a G80?? regards Kenny.

Probably, but what year is your bike; e.g does it have manual or auto advance/retard?

Hello , The bike is a 1959, and is manual advance /retard. Regards Kenny.

Are you talking about it slipping in use or whilst setting it. If the latter don't try to set the timing with the mag sprocket loose. Tighten this one up and loosen the sprocket at the cam end to set the timing. Once set, tap the sprocket onto the shaft (using a socket which will clear the nut) then tighten the nut. This should stop it moving as you tighten.
The only time I have had the timing slip was after a heavy kick back, ie. a sudden reverse of direction. What were the symptoms?
By the way a 59 G80 would not normally have a mag with manual advance unless it was aa G80CS

Have you tried gently lapping in the taper on the sprockets?

Hello, Clive Yes the timing slips after it has been set following the method you suggested, The bike starts first or second kick runs until the engine is stopped, and refuses to start, check the timing and it is retarded! There is a very good video on timing the mag tightening procedures etc which was followed to the letter, Also I am aware that the 1959 G80 would not have had a mag fitted , this was carried out by a previous owner namely, Simon Linford, who knew what he was doing.

Hello Duncan, as stated in my reply to Clive yes we lapped in the taper between cam and sprocket.

So is it just that the sprocket slips on the armature spindle, which implies taper wear on spindle or sprocket at the mag end, or similar at the camshaft?
If horribly worn the tapers might not mate whatever you do, but it may be that a thicker washer under the mag sprocket nut would ensure the parts went up fully tight before running out of thread on the drive end (with probably a compensatory adjustment of the mag on its platform to maintain chain alignment).

I'm guessing the mag that's been fitted is probably a manual Lucas N1-4, with face cam points , or perhaps an NC1 version with a camring? There can occasionally be problems with the contact breaker attachment or set of the camplate / ring on either version, but unless you've already had to play with those parts to regain the correct setting, probably not an issue.

Hello, I suspect the camshaft taper and sprocket are the issue, the mag sprocket takes a bit of effort with the puller to remove once it has been tightened, whereas the camshaft sprocket is relatively easy, so that will require some investigation, As a matter of interest the engine ran well prior to the bottom end having some attention.

Add some witness marks to narrow down what's moving?