With the standard Comet Inner Primary Chaincase (T4(2)) there is very little clearance between the spigot that protrudes from the back of the chaincase where the gearbox mainshaft passes through and the nut which secures the gearbox sprocket on the output gear of the Burman gearbox. The spigot on my original T4(2) has slight signs of wear from contact with the sprocket nut at some time in the past. However, it is important that the sprocket nut is held tight and this is the function of PR50-17-1BA. Omitting this lockwasher will liberate a little more clearance but the nut will have to be secured by another method and it would appear that centre punching has been resorted to in the past on a number of Comet gearboxes. Alternatively, one could reduce the height of the spigot.
Interestingly, the special inner chaincase which is supplied with the Alton Comet Electric Starter kit does not have a spigot at the rear of the hole where the gearbox mainshaft passes through but is completely flat. Whether this will lead to loss of lubricant or contamination with road grit entering remains to be seen. However, it does away with the clearance problems and one can fit the sprocket lockwasher without any concerns!
Peter brings up the interesting subject of chainlines. I'm sure that like many others I have just re-assembled standard bikes by the book on the assumption that the two Phils would have ensured at the design stage that the sprockets line up. However, when fitting the Alton kit it is necessary to shim out the new engine sprocket to line up with the clutch sprocket (and also shim out the sprag clutch to line up with the starter motor sprocket). This task is more difficult than one would imagine as it is not possible to put a straight edge on the sprockets but, having checked the primary drive, I thought that I would check the alignment of the final drive. This too is complicated by the fact that the rear subframe is not symmetrical and that the pivot bearing is offset to the rhs of the bike.
My calculations indicated that the gearbox sprocket and the rear wheel sprocket were more than 5mm out of line. Examination of the old sprockets confirmed this as the in-board side of the teeth of the gearbox sprocket and the out-board side of the rear wheel sprocket showed signs of wear. It maybe that my RFM is bent but the rear dropouts are perfectly aligned so I don't think so.
I believe that this chainline error occurred because the Comet was built around existing Series B Rapide components and a bought in gearbox and a compromise was needed. I have been able to correct 3mm of the error by putting a spacer under the gearbox sprocket (the maximum possible at that location). Full correction would require moving the rear wheel sprocket 2mm inwards - not an easy task while retaining the standard sprocket on brake drum flange set-up - so I think the chain will have to put up with the remaining slight misalignment!
John