I was having a small problem with a oil leak around the prop hub seal. The area around the seal would have an oil film and after flying a few hours a light oil mist would be on the windshield. I built a reed valve like the 1/2 VW boys use to run a neg pressure in the cut case VW. Made from steel feeler gauge material maybe .005. Mounted it in the alum box bolted to the gen stand location with a thermos bottle sealed plug to add oil. The oil goes under the reel valve. With running a vacuum in the crankcase, you have no oil leaks and the prop hub area stays dry. I did like the VW company and ran the 3/8" breather line to the intake of the carb. I have a fiberglass tube that runs from the carb intake to the airfilter box. Drilled a hole about 2" in front of the carb intake and cut a bevel on the end facing the carb and epoxyed to the FG tube. Now with running a vacuum in the crankcase, I have no oil leaks. The area around the prop oil seal stays dry. You also will get a small increase in power by the crank running in a vacuum.
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