Took apart 2 oil pumps today and the wear clearly showed how they had been assembled. The better pump had the dimples reversed. These pics are of the pump that's pumped more grit.
Intake/outflow Faces:
On the pressure pump, the oil seal keeps the center of the inner rotor from rubbing against any metal. A ring around the shaft showed linear milling marks, not concentric-ring wear marks. The inner face of the inner rotor of the scavenger pumps had slightly MORE wear near the shaft instead of less.
The outer rotor showed more wear around the outer 3mm where the pump body is continuous. There was less wear where the rotor mates against the cutouts for oil intake and outlet.
Blocked-off Faces:
The wear on the outer faces on both pressure and scavenger pumps was more uniform. The rotors rub against a continuous surface from the shaft to the outside edge.
The hardest to identify was the inner rotor of the scavenger pump. On both pumps that I took apart, the other 3 rotors were easy.
(Language collision. Two pumps each have two pumps within them. Then there are inner rotors and inner faces and outer rotors and outer faces. It's not your fault if you don't understand what I wrote. One pic . . . really isn't that sharp either.)
Grinnin:
do you have any idea of the genre of the pump that had the dimples reversed, i.e., was it from a post-1975 bike? Curiosity is striking me...I currently have about 12 oil pumps, but all are from 1975 or earlier engines, all had the dimples the same way in this collection.
What brings this up is: your mention of the seal ring wearing into the rotor. On all of the pumps I have, the seal ring is well-embedded into the body (makes it a major pain to remove) so it can't possibly touch the rotor, and on all the pumps where I have changed seals, likewise. BUT - I don't think I have [at least recent memory] changed a seal inside a post-1975 pump in a long, long time, as all those later engines I have rebuilt (10 in the last 8 years) had good oil PSI to begin with, so I let sleeping dogs lie in their pumps: they typically have less than 25k miles on their clocks. (Most K5 and earlier bikes I see have 50k or 10+ sitting years on theirs, seal leaks then.)
There were a lot of "cheapening" steps done in the post-1975 engines to save $ in production. I wonder: did they start fitting the rotors whichever way they would spin, instead of the match-lapping (time intensive!) process that was obviously used in the earlier engines? I find this interesting overall, because in the post-1975 engines more oil was restricted from the top ends (i.e., smaller oil orifice by .002") to increase flow to the crankshaft - this is partly why the top ends get so hot and wear the parts up there faster on these later engines. If Honda was not paying so much attention to the later oil pumps, this may have been their Warranty Engineers' tweak to ensure engine longevity in the bottom end? The later engines also had a 500 RPM higher redline (especially used in the "F" bikes), so this is why I previously thought the orifice change was made, to support the crank bearings. Could be wrong?
