Anti wet-sumping ball valves

I really wouldn't bother. Putting a devise reliant on negative pressure/suction to open the oil supply to the engine is an accident waiting to happen. The only place for such devices is on the pressure side of the oil pump. A company called AMR in the USA does a modification which reportedly works very well. My Mk3 factory fitted device works very well too so have not needed to use the services offered but I think would be money well spent in your case. 

The only valve/tap i would recommend is one that has an ignition cut included to prevent starting unless the valve/tap is open. ANY other kind is a disaster waiting to happen  

Google 'oil tap with cut out switch'

Hello Richard - try:

https://www.kingpincomponents.co.uk/all-products?page=2

HtH

6v is irelevent. Relays are NOT needed to handle the magneto. You must have a magneto with the electric kill, as used on the K2F/K1F. If any one is fitting any 'oil switch' and they are not sure about the Electrical side of it get in touch.

Thousands of Velocette owners have covered millions of miles on machines fitted with ball-and-spring check valves, and the only complaints are that they are fail-safe — in other words, their only failure mode in practice is to let oil through to the crankcase.

My understanding is that the RGM design is essentially the same as the Velocette item, and I would have no qualms about fitting one. (Hot tip: do not attempt to correct a leaky valve by tapping the ball onto its seat. This destroys the knife edge and merely makes the problem worse.)

Before someone replies that this is all very well, but Velos have roller big ends that do not rely on substantial oil pressure, consider that lack of lubricant will wreck a roller bearing as surely as it will a plain one — just more slowly.

I note that owners who vehemently complain that their check-valve failed and ruined their engine never seem to confirm that they had carefully verified correct oil flow following the last previous disturbance of the oil feed arrangements.

The only caveat relates to the nitrile covered ball that some suppliers offer as a replacement for the standard steel item. There have been reports that an engine backfire, and consequent reverse flow of oil in the feed pipe, can force the nitrile ball onto the knife-edge seat such that the latter cuts into the nitrile and retains the ball against the pressure differential.

The solution to this issue for Velo owners is obvious.

On my Commando I have fitted the Holland Norton Works version of the idea, which uses a (much larger) steel ball on a nitrile seat.

One drawback is that the valve makes oil changes slightly more tricky. Ensuring that the pump and the pipe between pump and valve is filled with oil. The pump can't suck air enough to open the valve.

Another roller bearing crank bike fitted with a hand operated valve managed 10 miles before seizing with valve shut. So a engine cutout is recommended.

The problem with many Norton twins is excessive clearance between pump body and the gears. With a spring one way valve fitted before the pump, when not in use the valve will prevent the tank draining but the oil between the pump and the valve can and will drain away given time. On start up the pump suction will fail to open the valve due to an air lock resulting in no engine lubrication. This has happened to at least one club member.