Small Engines (Lawn Mowers, etc.): 16.5 hp briggs and stratton motor, overhead valve engine, crankcase breather

Question
Hi ive got a 16.5 horsepower briggs and stratton overhead valve engine. (vert. shaft) this motor runs good, idles up and down fine but it blows oil out the crankcase breather tube (it goes up into the air filter) i took the breather off and cleaned it, its fine. i turned the motor over while watching inside the crankcase breather area and theres a small hole in the bottem and about 20 to 30 seconds after turning it over oil started coming out this small hole. evidently its getting enough oil up into the crankcase breather area and its coming out the tube after running a bit. i changed the oil (30 wt.) and filter but that didnt help. again this engine runs good, doesnt smoke and idles and revs good.  any ideas?   thanks jonathan

Answer
jonathan

The purpose of the crankcase breather valve is allow the air in the crankcase to escape. The engine must have  vacuum to operate properly. It has a one way valve that allows air out but outside air cannot get in. If the air cannot escape the air pressure builds in the base and blows oily/air mist  out of the breather. Thats why make sure that the dipstick O-ring is good and tube is tight. There are other possibilities , I hope this explanation helps you.

Also too much oil in the engine is the leading cause of oil coming out of places from which it should not.

You advise, with the dipstick screwed in, the oil level is halfway between full & add. Depending on several factors, it's possible your oil level may indeed be on the high side. Check the operator's manual to see if it says to screw in the dipstick or not when checking the oil. Also, make sure the crankcase is level when checking the oil.   ...

Check to make sure that the rpms are not out of wack.Over revving is the cause for this a lot of the time. Around 3500-3600 should be good .