Negative crankcase pressure

[Brian Rupnow]

I read yesterday about a small single cylinder i.c. engine model that had a "regulator" that kept a slight negative crankcase pressure in the engine while it was running. This was a 4 cycle vertical engine with a "wet" crankcase. The negative pressure kept any oil from migrating out around the crankshaft bushings. I hadn't heard about that before and I think it is a great idea. The engine in question was the Silver Angel by Bob Shores. A visual inspection of this engine running on YouTube shows no connection from the carburetor to the crankcase. The only "oddity" I see is that the engine seems to have double oil filler caps side by side. Does anyone have more info about this?---Brian

 

[Brian Rupnow]

I googled this, and came up with a video showing how it is done. Seems it is a one way reed valve on the crankcase. The reed valve blocks outside air from entering the crankcase when the piston is moving away from bottom dead center, but allows air to escape from the crankcase when the piston is moving towards bottom dead center. The net effect of this is to maintain a slight negative pressure in the crankcase. I'm not sure how to apply this to a model engine, but this may be a purchased item. Any ideas?

 

[ddmckee54]

Back in the early 80's I had an after-market system like that for my '57 Ranch wagon. It was called the Vac u pan and I think Edelbrock made it. I just Googled it and it's still available from various sources. It consists of 2 parts for each bank of cylinders: a tube about 6" long - that was cut off at a 45° angle, and a check-valve. The tube was welded into the exhaust with the face of the 45°cut parallel to the exhaust flow. The check-valve was installed in the valve cover. You ran a piece of rubber hose between the two. It was supposed to keep the oil inside the engine. It seemed to work, at least while the engine was running.

If you had it installed right, the exhaust pulse flowing past the tube would create a low pressure area at the end of the tube. Since the tube was hooked into the valve cover, every exhaust pulse would help to create a low grade vacuum in the engine.

Something like that should be doable. The fiddley bit would be the check-valve, but that's no different than the inlet valve on a pulse jet engine.

Don

 

[tornitore45]

2 strokes model airplane engines have reed valves. One can be made out of a feeler gauge leaf of a thickness found by experimentation.

 

[canadianhorsepower]

Brian
this as been on motors for decade. It's A PCV valve, Positive Crankcase Ventilation Valve
lawn mower, snow blower they all have them. check the video.
now to use this on a model engine simply make a hole in your base , instal a hose put a PCV in it




enjoy