Oil
Bypass
Valve
The bypass valve (located
to
the right and behind
the
gear
cover, Figure 9-19), controls oil pressure
by allowing excess oil to flow directly back
to
the
crankcase. Normally the valve begins to open at
roughly 13-14 psi on BGM gensets,
or
19-21 psi on
NHM
gensets.
FIGURE 9-19. OIL BYPASS VALVE
9-12
Oil
Bypass
Valve
Test
The bypass valve is non-adjustable, and normally
needs no maintenance. To determine if abnormal
(high
or
low) oil pressure is caused by improper
valve operation, inspect
as
follows:
1. Remove the 3/8-24 x 7/8 in. (BGM)
or
3/8-24 x
1 in. (NHM) capscrew behind the
gear
cover
and under the governor arm.
2. Remove the spring and plunger with a mag-
netic tool.
3. Determine the proper valve operation by
checking the spring and plunger against the
measurements listed below:
Plunger Diameter ....................
0.31
05
to 0.3125
in.
(7.89 to 7.94
mm)
Spring
Free
Length ......................... 1.00
in.
(25.4
mm)
Load
............................
2.6+0.21bs
(11.6+0.9N)
when compressed
to
0.500
in.
(12.7
mm)
4. Check the valve seat, and clean away any ac-
cumulation
of
metal particles which could
cause erratic valve action. Verify that the valve
seat is concentric with the larger diameter
valve bore.
5. Clean the plunger and spring in parts cleaning
solvent, and reinstall.
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