Hi Colin: I feel you buddy, you have spent a lot of time and have demonstrated neat and straight forward work. Here are a few observations.
In your earlier list of things done, you make reference to a rubber washer under the head of the crankcase drain plug. This really must be either fiber or a metal crush washer in copper or aluminum. The plug must be secure. Vibration, and you will have plenty, could cause the plug to fall out with life threatening consequences.
If you did not have a chance earlier, download this British Army reference manual on maintaining these bikes and go to Section 4: Oil pumps. Here's the link.
http://archives.jampot.dk/book/Workshop ... ndards.pdf
Section 4 contains the physical measurements for the oil pump spindle and pump bore, scavenge and supply. Note columns 2 & 3. Pull the rear cover plate from the engine, strip out the spindle, and measure and inspect everything.
Please note: Attempting to get a clear measurement with ether a dial/vernier/digital caliper will result in a false reading. As will inserting the new pump spindle, 'big end first' to gauge the fit. The pump bore is worn "barrel shape'. There is zero wear directly under the cover plate and measuring this aperture will not help. You will need a telescoping bore gage or ideally 3 point bore gage. Caution Here! There are multiple ports inside the pump bore which can "trap" a telescoping bore gage. Assuming the bore has 'acceptable' dimensions, inspect with strong light and perhaps a borescope. Look carefully for scoring inside the pump bore, where the scavenge port on the inlet side, meets the port in the pump spindle. The usual failure mode here is; swarf sucked into the pump bore is partially trapped by the pump spindle and a
trench is plowed in the pump bore as the spindle rotates.
We all know that most all pumps are far better at
pushing than
pulling. The smart farmer always had a pail of water handy to
"prime the pump"
And to your last question,
No, there are no check valves. AMC relied on an oil film in the pump bore to support a partial vacuum, lifting the oil, half a foot, where it could be pumped up to the oil tank. In the off cycle, oil would slowly seep back down the return pipe replenishing the oil film in the pump.
Section 4.jpg
Telescopic.jpg
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