Hmm...looks like someone thought those little holes weren't big enough?
In the (2) oil jets of that type I have seen apart (both from K1 engines), the body of the outer shell that was crimped to hold that screen in place was blocking all the holes in the perimeter of the jets, leaving just the 13 holes in the center area open. Is that one like that?
I went and dug out my old certified (machinist set) drill bits to measure the oil holes in this #1770 head and found the actual oil hole size is 0.045" at the stud's opening. pic below. The left one is ever so slightly looser, but the 0.047" drill won't pass thru.
I probably should mention something about flow dynamics here, which is: if the hole's length exceeds 3x the hole's diameter, restriction at a given pressure begins to cut off flow. So, in the case of these oil "jets" they did not flow anything close to the flow of the larger ones shown above, even given that those larger ones have a smaller output hole. The larger ones, though, do flow considerably more than the smaller aluminum 7-hole-filter versions found after 3/72 builds, as those aluminum ones have a pretty long neck where the filter holes are located. I'm thinking that those later jets could benefit their later heads by opening up the top metering hole a few more thousandths, and drill that size down thru the others except for the bottom one. I need to go dig up my old flow-calc texts and find those formulas...hmmm...
In the meantime: I think that those texts might also have the restriction values for the length of the holes in these sandcast heads, which should allow for calcs of both the current flow with this LONG feed path, and how much flow is DESIRED from the newer jet, which in turn should give us a drill size number for these old heads to make them flow like the later heads do. The early dome-filter jets have at least twice as many feed holes (and a pressured reservoir) behind the metering jet than the later ones.
Another take: if the upper portion of the metering hole is made wider than the orifice at the engine-stud hole then the smaller hole will meter the intended flow without the long-tube restriction. It does not, however, solve the need for a strainer, which Honda obviously decided (and so have I after the pictures above) was necessary, and came at no small cost in the later K0 production engines.
I'm thinking that would be a good idea? I remember my Honda mentor telling me that when he finally rebuilt his sandcast (over 100k miles) that his cam was sorely worn and the rocker feet accordingly, but he only replaced the rockers, for a reason I don't remember. When I tore my K2 down and measured everything at 130k+ miles I decided to replace the cam with a K4 cam to increase the lift a little more, but the rockers were/are still good and are my spares (I had the K4's rockers and cam bearings so I used those as they already matched). But, I have been more religious about oil changes over the years than are many others.
