Sorry, not a direct answer; I've always used an Allen key and positioned it right in the center of the hole. But if one end or the other of the tool causes the timing mark on the rotor to line up with the needle in the primary case, and the other end does not, that would be a strong clue, provided the alternator rotor is OE and not damaged. I think you'll find that the difference will be very slight; there are only a couple of degrees of crank rotation between the top and the bottom of the timing slot inspection hole.
Interesting my manual has the A50 plug end at 34 degrees, and the A65 side at 37 degrees. It says " Insert the peg with the appropriate model number uppermost." 66 manual. I have not seen a 67 manual yet.
Last edited by Roadwarrior; 07/14/1710:54 pm.
73 Triumph T140 Main Ride 70 Bonnie 67 BSA West Coast Hornet
When setting the static timing for a 45 year old motorcycle, it almost doesn't matter which side of the plug you use.
You are only getting the static timing in the ballpark so that the bike will start and you can then REset the timing two different ways:
1) With a strobe light.
2) By actually riding and testing the bike on the road.
The 1966 specifications really don't mean much in 2017. The gasoline you use is completely different. The combustion chamber is likely to have bits of carbon and coke or sharp spots that can cause preignition. You really need to take the bike out on the road and see how much advance it can stand in its current condition and with the kind of gasoline you burn.
People get all knotted up trying to set the timing EXACTLY PRECISELY ON THE DOT to the old spec, and then end up having to retard the timing 3 degrees or whatever so the thing won't "ping" going up a hill. Might as well go ahead and test it anyhow ..... !
The earlier timing spec for the a65 was 37 degs. They changed it to 34 at some stage. maybe it was because people's fingers were falling off due to vibration. If you can get away with running 34 degs on pump fuel now you are doing ok but a lot of blokes back it off another couple of degrees to stop pinging. The ET ignition setup also used a slightly more advanced setting. The 34 deg plug set up is a 'get you running' thing, like strobing at exactly 34 degs..... riding the bike is the best way of determining if 34 is too much.