Hi,
I noticed a slight ticking from the timing side of my Mk2a Commando that was bothering me for some time so I decided to investigate the cause as nothing appeared amiss on cursory inspection.
What was unusual was that I was able to rotate the triangular washer (using a small instrument screwdiver) behind the crankshaft timing pinion even though the 6 start pump drive nut was fully torqued. This indicated that there was no clamping of the dished washer, the triangular washer and the crankshaft pinion although the nut was fully tight.
Looking at this from several different angles, I noticed that the timing pinion did not mesh fully with the intermediate gear, although not a major issue, perhaps 1/16 inch at most but being further in towards the triangular washer.
Further investigation of this revealed that the oil drive nut, the left handed threaded one, seemed to abut on the crankshaft stepped radius before it clamped the pinion gear and associated washers. The crankshaft had not been damaged or altered in any way and I thought this may have been a design or manufacturing anomoly.
As I had two such engines, restored into one running machine, I had a spare set of washers and pinion gears and found that a .050 inch plain steel washer had been installed between the timing pinion and triangular washer thus preventing the nut bottoming out before clamping the pinion by the factory, evidenced by witness marks, see pictures.
I have posted this as others might have this issue and for some reason this washer is not illustrated in parts books or the Norton manual. If this lack of clamping of the pinion gear was to continue, the transmitted load that turns the cams would be borne by the key and could and in extreme cases fail thus causing engine damage. Woodruf keys are not for transmitting loads, they are for alignment purposes only, either clamping of the gear or via a taper joint are where the loads should be transmitted. The pinion was loose and there was perseptable backlash that indicated that the key had worn and replacing it restored the zero backlash on the shaft, so I was lucky.
The ticking noise was created by the gear chattering and would have most likely continued for some time before failure of the key.
See attached pictures indicating the witness mark of the 0.050 washer that was omitted from my last build.
So the moral of this story is to check all clearances and clamping of pinions where required, don't trust the parts book to show everything.
Regards
Steve
