I think another consequence of my “benign neglect” of the BSA has surfaced: The clutch started slipping, just as I was headed out on the first real ride in years on it. You can see by the photo above that I dismantled the primary case to investigate.
As seen above, the seal had failed on the tin cover which in theory keeps the primary case oil out of the clutch, and a dry clutch covered in oil doesn’t work very well (modern bikes use clutches where the friction plates run in oil). Furthermore, looking at all of the parts involved, it must have been a hurry-up-and-wait day at Roger’s Resto Shed when I put the primary side together…there is no way the cover and its gasket had a chance of sealing against the chainwheel assembly, given its condition. But apparently I thought it was “fine”.
You can see there was also a missing nut on the cover, which I could not find anywhere in the case and which could not have been helping.
The chainwheel, which incorporates the outer clutch housing, is past its sell-by date, so I have feelers out for another. However, it has been 70 years since they have been made and they are few and far between now, though one supplier I called thinks he may have a complete plunger-frame A10 clutch in his stash. Let’s cross our fingers!