Keith I know that there are only two cams in Merlin, well I should do since I have had the pleasure on working with several engines (actually Meteors not Merlins, and one 18 litre Rover V8 version of a Meteor from an Antar) so why did I put four cam, well I meant twin cam, but that usually refers to two cams on the same head, four valves for sure, and dyslexic as well !
I always pack the oil pump chock full of CLEAN Vaseline, vital in some motors (Rover/Buick 3500), advisable in others, and a waste of time in many (such as Ford) but it can never do any harm, the oil in inevitably "sucked" up from somewhere, so the dip pipe will be full of air, with Vaseline a true vacuum is created on initial turning of the motor, the Vaseline can go wherever it likes up the outlet side of the pump, in a slug of the stuff even, but it will pull the oil in as well, it will do no harm and can do a lot of good, it melts readily in warmed engine oil, and is made from petroleum anyway. its best not too leave it for many weeks before you do the initial turn of the motor, but when you do this to a triple, you will be astounded at how quickly the oil is pouring out of all six cam bearings, and not a sign of Vaseline in sight. Many times I have had people phoning me to say that they are ready to run their rebuilt triple and have cranked it (no fuel in carbs) until the battery is flat and no oil showing at the cam bearings, they recharge it, and have another go and all is well, this method saves all that, just a few turns and Robert is your fathers brother. Many just start the thing up!
CLEM