LUBRICATIONBreathersFig. 7. Model Series 146700, 170700, 190700, 251000Fig. 8. Model Series 170400, 190400Fig. 9. Model Series 300000, 320000It is the breather’s function to maintain a vacuum in thecrankcase. The breather has a fiber disc valve, whichlimits the direction of air flow caused by the pistonmoving back and forth. Air can flow out of thecrankcase, but the one way valve blocks the return flow,thus maintaining a vacuum in the crankcase.A partial vacuum must be maintained in the crankcase toprevent oil from being forced out of engine, at the pistonrings, oil seals, breaker plunger and gaskets.Checking BreathersIf the fiber disc valve is stuck or binding, the breathercannot function properly and must be replaced. A .045"(1.1 mm) wire gauge should not enter the space betweenthe fiber disc valve and body. (A spark plug wire gaugemay be used.) Check as shown in Fig. 10. NOTE: Thefiber disc valve is held in place by an internal bracketwhich will be distorted if pressure is applied to the fiberdisc valve. Therefore, do not apply force when checkingwith wire gauge.Fig. 10 Checking BreatherIf breather is removed for inspection, or valve repair, anew gasket should be used when replacing breather.Tighten screws securely to prevent oil leakage.Most breathers are now vented through the air cleaner,to prevent dirt from entering the crankcase. Check to besure venting elbows or tube are not damaged and sealproperly.Various breather assemblies are illustrated in Fig. 11.3
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