OK, so here's how it went: I pulled the pump back off and measured .005" total difference between the pump body width and the width across the gears, about evenly split between the scavenge and supply sides. I decided not to do anything about the scavenge side [I guess by default that makes me a supply-sider...]. I set to work on the pump body with 400 paper, but sure enough, and against the admonition of the manual, I got impatient with the rate of removal and switched to some medium emory cloth and took too much off, to the extent that the pump would bind up completely with that last twist of the body screws. But to fix my screwup, rather than lap the gears, I just "broke it in" by working the pump by hand, keeping some tension on the screws and using some old clutch oil left over from kart racing days to keep the brass (bronze?) from galling. Pretty soon I had the right degree of dry tightness/lube freeness, and in it went (after cleaning, etc.). I put three shims under the pressure relief spring, making a total of four (turns out there was one in the cup already). After setting the slack in the timing chain - and grumbling that my reference marks on the Boyer were now worthless and I would have to retime the engine - I put on the timing cover.
Then I got a big surprise. I have one of those inline anti-wetsumping valves, which looks like the upper one in the picture here <http://www.clubmanracing.com/images/N201Wjpg.jpg>. I disconnected the downstream hose to fill the pump inlet, and when I put the hose back on the spigot and went to snug the hose clamp, the worm gear slipped a cog, preventing it from tightening. Criminy! If this clamp failed when I was out before, the pump could have sucked air, leading to the loss of oil pressure! More grumbling, since that would mean I had wasted my time reworking the pump. Oh well...
After replacing the hose clamp, I pulled the plugs and kicked the engine over until both legs were aching, hoping to see some pressure on the gauge. But nothing.
On to the moment of truth: fuel on, choke on, tickle, two kicks, contact, kick (I won't say how many - timing was approximate), start. After a few seconds and one goose of the throttle and no pressure, I shut it down. Very dark mood ensues...
As noted previously, I had checked the wetsump valve when I went through the system before, but just to absolutely eliminate the possibility that was the fault, I replaced it with a WOG ball valve from the hardware store. This time when I started the engine, the pressure zoomed to 75-80 max, and about 45 at idle. Hallelujah! So now that I'm in business, I shut it down and take two shims out of the relief valve and restart. This time, 55-60 psi, so I add back one shim and get 65-70 psi max (data point: one shim = 10 psi). I set the timing with a light. By this time the day has cooled and it's nearly dark, so I decide to wait until the next day to make my confirmation ride.
Yesterday afternoon, with it cloudy and in the high sixties, I took it out. Just an easy ride around the neighborhood, keeping it between 2500 and 3500 mostly. As the engine warmed, the max OP gradually declined, but nothing alarming. Then after I had gone 2 or 3 miles and maybe 10 minutes, the needle started dropping precipitously - oh $hit. I turned around to head home, wondering how far I'd get before having to kill it. Only this time, the needle didn't go all the way to zero, instead stopping around 10 psi or so, eventually settling at 8, which it wouldn't exceed even during a WOT burst or two. Having previously reasoned that the engine may or may not live with no pressure showing, but can live with some pressure showing, I rode on home. At idle in the driveway, it fell to zero psi.
So, back to the original question: where was my oil pressure the other day? Could be any of five possibilities: a) pump sucked air, destroying prime; b) wetsump valve constricted supply, starving the pump; c) lossy pump couldn't keep up with clearances in the rod bearings, which I have now partially fixed with a partial refurb of the pump; d) 20w-50 VR-1 is too thin for warm weather; e) it's a Norton.
From here, I'm going to leave the ball valve in - with an "interlock" link between the handle and the kickstart lever - and see if I really have a wet sump problem: leave valve open at shutdown, set engine to TDC, observe oil tank level prior to next startup. If no problem, replace valve with straight hose. If problem, contemplate my choices for a permanent fix - as well as whether I'm ready for a rebuild yet.
Further discussion welcomed. For instance, am I using the right oil?
"Carry on, and dread nought" - Winston Churchill
