AMC gearbox sprocket

I suspect your new one actually measures 0.375" width (3/8").

There are two rear chain sizes used ; 5/8 x 1/4 (520 chain) and 5/8 x 3/8 (530 chain) - the second dimension of each being the width.

so there are two widths of gearbox sprocket - 1/4" to 1965 and then 3/8 " thereafter.

Have a look at the RGM website (others are available of course!) and you will see both listed ina range of tooth counts

Colin, you are right except that I always understood that the change of sprocket size was made in 1964, along with the move to 7 3/8 yoke centres.

Micheal, the main thing is that your gearbox sprocket matches your 42 tooth rear sprocket. As Colin says, there is a good choice of sprockets at RGM. If you are using a 21 tooth engine sprocket you might want to consider a 21 tooth gearbox sprocket if more relaxed cruising is your thing. On the other hand, if the traffic light GP is what you want then maybe an 18 tooth gearbox sprocket will get you away from the lights faster, all assuming keeping the std engine sprocket? 14 teeth is the std gearbox sprocket size.

BTW, if the gearbox sprocket is hooked then have a close inspection of the rear sprocket. (Both sizes available)

14 teeth is the std gearbox sprocket size.????? Possible typo???

Perhaps 14 on a Jubilee.........most AMC gearboxes came with a 19 tooth. Even the first Commandos.

Check that the teeth on the rear sprocket match the width size of the Gearbox sprocket.