1961 model 16 oiling problems

[Don Madden]

I have found two common causes of single cylinder plunger pumps not returning the oil properly while the feed pumps works normally. As the plunger rotates & moves forward, the first half of the stroke has not yet uncovered the entry port, creating a partial vacuum. If the rear plate does not seal airtight the vacuum is destroyed & half of the stroke is ineffective, not enough to keep up with the feed to the engine.

Twice I have cleared blockages in the drillways from the sump to the return end, a convoluted path. Pre-1956 had two drillways, one long one from the sump above the drain plug & accessable by removing said plug, to high in the case. Another long one through the pump bore that intersects with the first at a sharp angle. It was drilled through the threaded hole outside the pump cavity & the access hole then blocked by the 1/4in plug screw. If you have an air pressure nozzle with a long narrow tip you can pass it up through the threaded hole into the drillway to blow out obstructions in the direction reverse of normal flow to prevent further jamming of any obstruction. I have used long extention drills, one in each drillway, to fish out sealer & gasket debris.

1956-63 engines are more complicated as the magnetic filter plug, being longer, blocked the prior path from the sump. That drillway was moved outward, through the bottom of the case & up. The access hole is then blocked by a grubscrew, seen next to the drain plug. The two drillways do not intersect but are connected by a short drillway near the main bearing & then sealed by a brass plug driven in. External air pressure is the best way to clear these.

One way to blow compressed air through is to make a close fitting plug to replace the plunger. Then remove the screw plug & carefully drill a hole through the wood to line up with the drillway. This provides a path from outside to the oil passages.

Good luck! And cheers, Don.