Drilling tiny hole in motorcycle head

Is the oil pressure adjustable? If so, you can compensate for the added oil port. I think you have this well thought out with the replicable orifices. Do you use a synthetic oil? I'm a firm believer in it for outstanding bearing protection.

You could fill a syringe with hot oil and see how much pressure it takes to push this oil out. One of those meat injectors would work. Or, if a feed store is nearby they sell syringes cheap. Needles too. Calculate the area of the syringe and put a known weight on the plunger to see how much oil comes out. ERS

||This is a 70's Honda 400-four head. They (and the 350-four) had a tendency ||for the end cam bearing to fail - the camshaft rides directly in the ||aluminium head; the end bearing is splash-lubricated (so's the centre one, ||but it gets lots of oil and so does not fail). There's about 1/8 clearance ||at the end of the shaft and right beside it is the oil gallery for the ||rocker-arm spray-tube lubricator. || ||I think if I drill a tiny hole from the end gaps of the camshaft to this oil ||gallery it will feed the end bearing. || ||How small a hole? It might not matter if the bearing is tight, but if it ||gets loose then the feed to the rocker arms will drop and they'll fail. Oil ||pressure on these usually runs over 50 psi unless it's hot and idling. || ||How to drill? I think it might be better to drill and tap a big(ger) hole, ||and make a pair of brass inserts.

Carburetor jets Holley Jets are plentiful and cheap, but you may not have room for the head

Texas Parts Guy

Be careful! The oil you get to that bearing you will be robbing fron another dowstream. Get the hole too big and you just move the problem from one bearing to another