Steve The Longstroke A7 and later Plunger A7 and A10 engines all share the same common primary chain cover casting, 67 1701 but this is machined differently for early and later models to alter the oil capacity. As you can see, the level setting is the cutaway on one of the forward fixing setscrew positions in the lower run. Early models have this cutaway on the front lower screw position, a relatively high oil level, later versions its the next one back, (position B in Musky's diagram) reducing the level and published capacity. This capacity assumes the BSA copywriters got round to updating the service information way back when. Add to the mix Haynes covering all models, inaccurate conversions etc and it all adds to the confusion. The chaincase diagram here is more of a composite of both plunger and S/A cases, so not strictly correct in description.
In practice you want oil to lubricate the chain, not the clutch, and the chain just needs to have the chainwheel teeth dipping the oil. A method that works for me is use published figures only as a rough guide, but run the engine at tickover and add oil until droplets start to flick into view, indicating oil is up to the chainwheel. Add just a little more to give a fairly consistent stream of descrete drops for luck and that's it. That way you know the chain is lubricated, but the clutch stands a better chance of keeping dry.
Swarfy.
