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Thread: 1915 Harley Oil Pump Adjustment Screw

  1. #1

    Default 1915 Harley Oil Pump Adjustment Screw

    I am working on a 1915 Harley magneto model. I was hoping you might be able to tell me the correct length of the oil pump adjustment screw from the tip that contacts the plunger to threads at the base of the screw head. I think mine is either worn or shortened. See attached photo.

    Erik Bahl

    1929 BMW R63
    1915 Harley Davidson 11F Twin

  2. #2
    Join Date
    Nov 2001


    Yours look about right.
    Mine measures 1.1/64

    Pete Reeves #860

  3. #3


    Thanks Pete.

    I did a quick test and determined if the screw is seated with the head flush to the oil pump cover the oil plunger does not move as the rotary valve is rotated which should mean none, or a minimal amount of oil being pumped. If I back the screw out 1/4 turn I get slight engagement of the plunger. I want to experiment with the oil flow. My bike has oil rings on the pistons and the engine does not burn oil. Per documentation I found regarding the oil pump, it pumps 1/2 pint (8oz) of oil into the case every hour. I have measured the drained oil after a handful of one hour runs and I am getting ~8oz. My understanding of the stock design is that the engine wants ~2oz in the engine case and the excess oil that is being pumped into the engine each hour would have been burned or leaked out maintaining 2oz always. With the added oil rings, my engine oil continues to rise so I wanted to see if I could decrease the amount of oil pumped into the engine.

    Anyone who has different information, please correct me.
    Erik Bahl

    1929 BMW R63
    1915 Harley Davidson 11F Twin

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