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windy

J.A.P 250cc Sidevalve oil supply problem

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I am restoring a 1929 J.A.P 250 sidevalve engine which had previously seized its piston due to lack of oil. I believe overnight the oil would flow into the crankcase, giving the illusion of too much oil, so the pump was turned down, but as soon as it had used up this excess oil it then got starved. Where the oil externally enters the crankcase there is a small valve body, but when I looked inside there were no parts in there. From an old parts list I can see that there should be a single ball bearing, but I can't see anything else listed, and was wondering if there was usually a spring, to hold the ball bearing against the bottom seat, or maybe it might even be held against the top, like a one way valve?

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I am restoring a 1929 J.A.P 250 sidevalve engine which had previously seized its piston due to lack of oil. I believe overnight the oil would flow into the crankcase, giving the illusion of too much oil, so the pump was turned down, but as soon as it had used up this excess oil it then got starved. Where the oil externally enters the crankcase there is a small valve body, but when I looked inside there were no parts in there. From an old parts list I can see that there should be a single ball bearing, but I can't see anything else listed, and was wondering if there was usually a spring, to hold the ball bearing against the bottom seat, or maybe it might even be held against the top, like a one way valve?

 

It's not clear from your description if the engine has a pressure lub oil system or is splash lubricated (as is my J.A.P 6 series industrial engine driving an 1946 Opperman). I assume it is a motorcycle engine with separate oil tank. A tiny spring and ball bearing seating as a seal may act as a pulse pump regulating oil into the c/case and will need to be calibrated by adjustment to balance the oil burnt by the engine dependant on wear and use. Modern garden tractor engines use crankcase pulse pressure to drive fuel pumps with a rubberised membrane acting as a non return valve to pump fuel up to the carb, using much the same principle. Good luck. Jerry

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It is a motorcycle engine with external oil tank, pressure fed total loss system from an adjustable flow Best & Lloyd oil pump into the crankcase. The problem seems to stem from the lack of internals in the little valve where it externally feeds into the crankcase. Ideally I need to know what the internal components of this valve are, and their orientation.

Edited by windy

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Just for reference in case anyone else has the same problem, this is the answer, a circular piece of 15 thou shim steel;

JAPdiscvalve001_zpsd2d4002c.jpg

Also note the valve body should be fitted the opposite way up than in the 1st pic!

Edited by windy

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