I have a 55 KH, and have had problems with it eating rings and oil for 20 years, actually a little more than 20.... We have tried all the recommendations, with still no results. The best rings I have found are Hastings with three Piece oil rings. The W models after 1952 used the same ring sizes as the KH and K models, but many of the after market pistons available for K models now are set up for the earlier W models with wider compression, or top two rings and thinner one piece oil ring. Well, the K models had a thicker one piece oil ring, but I prefer the three piece Hastings rings. The K model rings and pistons are much better than the others, that were cut to be cheep, as there is a plethera of those older style rings around.
Anyway, my motor had been rebuilt before I got it in 1986, and we kept the same pinion shaft. This is what runs the power from the fly wheels to the oil pump and the cams. It also controls the flow of oil from the pump, down the center of the pinion shaft, into a hole in the right fly wheel and feeds the oil through the crank pin between the fly wheels and the oil ends up feeding the lower bearings on the piston rods. Then the oil is splashed into the lower end, and oils the right side main bearing via splash along with the pistons and upper wrist pin bearings in the rods. It is kind of a long way to describe it, but that is how it is supposed to work. There are also side oilers on K models that spray oil on to the pistons, from a hole in the side of the cylinders. Hoping to reduce my oiling problems I plugged these up. It did not help.
We have now heard from an old school mechanic in the area that the flow down the pinion shaft is too excessive, and he came up with a left hand threaded Philips Head screw that threads backwards into the end of the shaft. We drilled a .090 hole in the screw, right in the middle of the Philips head slots. This he says will reduce the amount of oil building up in the lower end, as when ever I dip it or drain it, it is always about two to three inches down there, and that is about the height of the return slot to the oil pump. There is supposed to be much less, and feel that because the KH needs less oil than the OHV Sportster, the hole was smaller thought the pinion shaft. We checked on a later 1000cc Sportster fly wheel, and low and behold it was filled and drilled from the factory with about a .10 hole. The one in my shaft was about .18, so taking it down to .090 is a lot, but I have not run it yet, and it may just blow the thing to bits. I don't know, but will have it back together in the next couple of weeks. Just got the trans back in from, pulling the whole engine down, and splitting the cases to check the scraper clearances, which were just fine.
This time we also used a later 1000cc model breather with larger window in the breather valve shaft to get as much breath and oil out that is possible, something I learned from The French Owl. Anyway, still working hard to put it back together. Just a few days left, but will let you know. Last time I got it running, after torque plates being made for straight boring, and using total seal rings, it got a good 30 miles to a quart. Not too good!
Will let you know how it turns out. If yours is smoking, and is wet up top, do a search on my posts on "Wet up top", and learn the saga....
It was common practice to run a .060 restrictor plug in the cam cover on "R" motors. When I first built our KR race motor I had a sumping problem during races. Next time it was apart I took the time to build up the scrapers an get them closer to the flywheels, got the breather timing spot on and installed the restrictor in the cam cover. Fixed the problem. I use 15-40 DELO 400 oil. This is a high rpm motor so the .090 may be closer to what you need. Another thing that I have been using is a breather off of the rear of the camcover with a one way check valve. With this you end up with a slight negative pressure which calms the crankcase and helps ring seal.