F510 & F525 – BREATHER SYSTEM OPERATION
Maintain a vacuum in the crankcase to prevent oil leaks.
• Breather Valve
• Breather Passage
• Oil Return Passage
Theory of Operation:
The engine is equipped with a breather system that allows air to escape easily from the engine, but restricts air coming in. As the piston moves downward during power and intake strokes the volume of the crankcase (H) decreases. To prevent a buildup of pressure, oil-laden air flows through the breather passage (F) and breather valve (D) into the space under the rocker arm cover (E). In order to prevent excess oil loss, the air is routed through a maze (C) in the rocker arm cover where the oil separates out. The non-oily air then passes through breather hose (B) and into the air cleaner housing (A) between the air filter and the carburetor. The separated oil lubricates the valve train and returns to the crankcase through the oil return passage (G). When the piston moves upward during compression and exhaust strokes, the volume of the crankcase increases. Crankcase vacuum increases and closes the breather valve preventing air flow into the crankcase. A restriction (I) and oil in the oil return passage also help to limit air flow into the crankcase. The result is that a small vacuum is maintained in the crankcase.