I realized after re-reading my previous post attempting to explain how this pump functions that I had left out a rather important explanation of how the pump adjustment is achieved. This actually has more to do with the outer most small o-ring than I had said.
So you have the adjusting screw with it's tiny o-ring held in place by a flat head screw then the is a plastic plunger or sleeve that slides in the internal bore of the body against a spring that keeps the whole adjustment system under tension. Now as the adjustment screw is screwed in this pushes the plastic plunger down the bore. At some point the plunger passes by the two holes under the small o-ring and seals off the pressure release system. At this point the oiler is at maximum output as there is now nowhere for the pumped oil to go except to the bar. As the screw is adjusted out the plunger starts to expose the holes, releasing pressure and oiling falls off.......the further you adjust out the less oil goes to the bar and more oil is returned to the tank until the holes are totally exposed and you are now at the least oil to the bar. This all is contingent on all the o-rings and sealing surfaces are in good, clean functioning order. Kevin is right...this would be a good candidate to soak in the UC for a while. But is not as complicated as, say, a carb....the passages are all through bored so no blind stops or anything....the holes under the o-rings are rather large. I cleaned them up with a # 62 jet bit but thought even that was slightly loose...I think a regular 1/16" drill bit would work fine.
A lot of other oil pumps adjust the amount of oil pumped by altering/adjusting the length of the pump shaft stroke......these pumps don't....they pump at a constant rate varying with rpm. This is all happening at lightening speed as every revolution of the crankshaft is one complete cycle of the oil pump......which means that if the saw motor is turning 10,000 rpm the pump is cycling 166.6 times a second!!!!
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