AJS & Matchless Owners Club

Hi,
recently i bought G3L motor partly rebuilt seller said , bottom end rebuilt, rebore, and Norton piston fitted, not sure of quality, so stripped to find top ring large bit missing, so are the 350 Norton bits interchangeable with Matchless/AJS particularly the piston rings, or should i simply get a Matchless 350 replacement,
. Don't know what year the piston is from, does it matter.

If you don't know which Norton piston you have then you can only measure the rings (and the ring recesses in the piston) to find out if AMC rings will suit.
Perhaps you can send the Norton rings to a supplier to be matched for a new set.

If the Norton piston height/width/gudgeon pin diameter dims are different from an AMC piston and the cylinder was rebored to match the Norton piston then 'No' you can't fit an AMC piston without a further rebore and/or little end bush.

The 'partly rebuilt' claim gives me an uneasy feeling and why fit a Norton piston when the correct ones are available?
Does the cylinder bore look as though it has just recently been rebored?
As a matter of interest, what is th'engine number which is stamped on the crankcase?

BTW - You've put your post in the G80/Model 18 (500cc) section, not the G3/Model 16 (350cc).

A later thought...
Where is the 'missing large piece of piston ring'?

They aren't an exact match. The G3L is 69mm and the norton model 50 is about 71mm.
So could be used in a G3L barrell bored to suit. I can't see the point when the G3L pistons are available??
Cheers Dave.

Further to Sprid's reply - if the weight of the Norton piston is different to the AMC one, the crank may have been re-balanced to suit. If so, fitting a new AMC piston will shake your fillings out - may be cheaper to fit new ring(s) if you can.

Jim