HI Nigel,
I hav just joined the forum, but am a longtime BSA owner, restorer/repairer
The root cause of your problems is the oil pump I rekon!!!
OK so heres my experience of this type of failure, (not on my bikes though
)
1)low oil pressure due to bad, or porus pump body, worn timing side main bearing, or to tight bearing which has siezed on the shaft and the bush is turning in the steel sleeve!!
2) With low pressure the pressure relief valve does not open to bypass oil to fill the trough that the cam and followers run in. this leads to worn followers and eventually wrecked cam.
On BSA twins the first sign of problems is rattly tappets
3) Lack of pressure to the drive side big end, the rod should have a little bled hole in it facing up towards the piston, lack of oil leads to the left side piston siezing, then the rod breaks and wrecks the crankcases!!!
My advice to you is that you will have to strip the engine completely as there is now a lot of very nasty bits of cam follower in every concievable part of it, in oil tank, pipes and everywhere!!!!
A lot of owners complain about wet sumping on A7/10 engines, in my experience this is more often caused by the porus nature of the mazak (zinc alloy) that the pump body is made from
and or a little wear on the pump spindle which lets the oil leak past
anti syphon valves dont help here because the oil leaks out of the pump and then there is no prime in the pump to lift the anti syphon valve!!
My Super Rocket has modern pistons and runs at less than the original BSA specified clearance
and I have not had problems over 8000 miles,
I know an A10 owner who rebuilt his engine because the followers/cam were worn, new T/S main bush and bigends mains etc, it tightened after 50 miles or so but freed out again so he rode on, a couple of hundred miles later it blew up in a big way, breaking the drive side rod, holing the cases and wrecking the cylinder!
The cause of this was the oil pumb body was porus and the oil just leaked through the alloy, this is then picked up by the scavenge side of the pump and returned top the tank, showing normal oil circulation!
Apologies for being so long winded but there is an awful lot of mis information floating about
Regards
John O R