Having recently rebuilt the distributor for the Healey and having been a little unhappy whether I would get full advance, I tried it out, using a screwdriver in the rotor arm slot to gain the advance against holding the drive gear in the other hand. On my distributor, it makes no difference whether the screw is tight or loose as to how much advance you get. The possible amount of advance is the same. There is no spring washer under the screw on the (ex Mk I) distributor I am using and there wasn't one on the distributor that came with the bike either. Nor can I find one on the exploded diagrams so I don't think there should be one.
36 4G, 37 VH, 53 ex ISDT KHA (project), 54 KH(A), Healey 1000/4 (project)
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser.