Coco said:
You are correct in saying that the outer of the two pipes from the junction block is the feed side and the inner should go back to the oil filter.
In terms of fitting a valve, have you borne in mind that the Mk111 already has an anti-drain valve in the timing cover ? It is a small plunger which is held by a light spring against the (thicker than previous models) conical rubber on the oil pump outlet.
This is really the correct way to do things as any oil pressure pushes the valve open which means there is no possibility of oil starvation which remains a fear with in-line valves. The only problems are that Nortons probably erred on the side of caution by fitting a very weak spring and the small bleed hole behind the piston is so small that the it can effectively "hydraulic lock" and remain open. I have polished mine so it is probably a little undersize but moves freely.
If the plunger is stuck "open", it will look as if it's not there. Under no circumstances should you put one on top thinking that it is missing. Investigate first or you'll seize at the very least.
I still have doubts about after-market valves. If the spring is too strong then there will be starvation and even if not, it is an obstruction in the oil line to avoid something which is at worst only an inconvenience. A half-way OK oil pump will not let your tank drain from one weekend to the next, even if your valve is sticking open.
Obviously, this is only my opinion but I think that it could be another case where it will do no harm to run it as it is and see if you have a problem before you start looking for a solution
I haven't used my Mk111 for a fortnight and I've just checked the dip-stick which is still showing "full"
