Fig. 7. Model Series 146700, 170700, 190700, 251000
Fig. 8. Model Series 170400, 190400
Fig. 9. Model Series 300000, 320000
It is the breathers function to maintain a vacuum in the
crankcase. The breather has a fiber disc valve, which
limits the direction of air flow caused by the piston
moving back and forth. Air can flow out of the
crankcase, 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 to
prevent oil from being forced out of engine, at the piston
rings, oil seals, breaker plunger and gaskets.
If the fiber disc valve is stuck or binding, the breather
cannot function properly and must be replaced. A .045"
(1.1 mm) wire gauge should not enter the space between
the fiber disc valve and body. (A spark plug wire gauge
may be used.) Check as shown in Fig. 10. NOTE: The
fiber disc valve is held in place by an internal bracket
which will be distorted if pressure is applied to the fiber
disc valve. Therefore, do not apply force when checking
with wire gauge.
Fig. 10 Checking Breather
If breather is removed for inspection, or valve repair, a
new 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 be
sure venting elbows or tube are not damaged and seal
Various breather assemblies are illustrated in Fig. 11.