Author Topic: 1928 Douglas EW hand oilpump  (Read 2169 times)

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Offline patrickhowell

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1928 Douglas EW hand oilpump
« on: 03 Dec 2015 at 12:48 »
Having just finished the rebuild of my engine, I find the same problem as before, namely a pump which won't pump oil. All leather washers have been renewed, and their assembly is in accordance with the book. There is oil in the tank, and the pipes are clear. It almost feels like a vacuum or a hydraulic lock, not sure which, and installing or removing the spring makes no difference. Not sure what the spring does anyway, it appears to force the plunger up, which is surely the opposite of what is intended? Does the supply pipe need priming somehow? Any suggestions welcome, as obviously I don't want to attempt a start-up until resolved.

Offline Chris

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Re: 1928 Douglas EW hand oilpump
« Reply #1 on: 03 Dec 2015 at 15:30 »
Hi Patrick
    If you are talking about the main oil pump spring and it appears to be forcing the plunger up then you have the plunger assembly incorrectly assembled. The plunger knob when pulled up should be compressing the spring which then forces the plunger with its leather washers down compressing the oil drawn out of the oil tank when the plunger is pulled up. There should be three leather washers. The fixed one on the base assembly is there to seal the holes at the base of the oil pump body to prevent oil under pressure in the  pump body from returning into the oil tank. The two leather washers on the plunger are back to back. The upper washer pulls the oil out of the oil tank. The lower leather washer then forces the oil through the base assembly, exit pipe and the non return valve into the crankcase. In case of the washers leaking slightly permitting oil to pass the washers on the plunger there is a hole in the pump body nearer the top permitting surplus oil to drain back into the oil tank when the plunger is pulled up to prime the pump. Chris

Offline patrickhowell

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Re: 1928 Douglas EW hand oilpump
« Reply #2 on: 05 Dec 2015 at 08:02 »
Thanks, Chris. I don't think I described the spring problem too well, what I meant was that I couldn't get the plunger, with spring or without, all the way down its cylinder. However, by dint of constant hand pressure from on top, I was gradually able to force the plunger down and onto its thread, and it now appears to be working, so it looks as if it was hydraulic back pressure from the oil itself. A new problem emerges, though, namely that the oil drains into the timing chest by gravity, eventually exhausting the tank. As the oil tap has no 'off' position, this seems to be a design flaw; I would have put a three-way tap so as to provide for 'off', hand-pump only, and hand and mechanical pumps. Anyone else got experience of this?