Section X. VALVE OPERATING MECHANISM
excessive carbon MECHANISM deposits is minimized,
3-34. General
and promotes longer valve life.
a. Engine Model 687C-18-ES. This engine is a
twostroke cycle type with exhaust valves only, which are
3-35. Valve Operating Mechanism for Engine Model
operated by lobes on a camshaft located in right side of
crankcase. Cam follower rollers actuate pushrods which
687C1 ES
operates the rocker arm located on cylinder head.
Movement of rocker arm opens exhaust valve during
a. Removal and Installation.
exhaust stroke of the piston.
(1) Remove valve cover and gasket (TM 5-
3810-201-12).
b. Engine Model D333TA.
This engine is a
(2) Loosen locknut (7, fig. 3-42) and turn
fourstroke cycle type with exhaust and intake valves. In
adjusting screw (8) counterclockwise until rocker arm
general, their operation is similar to other engines. With
(16) is without pressure on valve spring (18).
addition of valve rotators that cause valves to turn a
(3) Remove two self-locking screws (6)
minute distance with each operation, the formation of
securing supports (6)to cylinder head (4).
1
Nut (24 rqr)
9
Push rod (6 rqr)
2
Stud (24 rqr)
10
Plug (6 rqr)
3
lockwasher (24 rqr)
11
Spring (5 rqr)
4
Cylinder head (6 rqr)
12
Sleeve (5 rqr)
5
Rocker arm support (12 rqr)
13
Valve spring (6 rqr)
6
Locknut, special (12 rqr)
14
Cap (6 rqr)
7
Locknut (6 rqr)
15
Valve keeper (12 rqr)
8
Adjustment screw (6 rqr)
16
Rocker arm (6 rqr)
Figure 3-42. Valve rocker arm, installed view.
AGO 20051A
3-52
