DESCRIPTION AND OPERATION
Page 57
Pinless Valve Yokes — Inlet and Non-Brake
Exhaust Valve Locations
Approximately two years prior to ASET™ engine
introduction, MACK standardized the use of
pinless valve yokes at all inlet valve locations,
together with standard push rods. Effective May,
2003, pinless yokes are also used at exhaust
valve positions of non-brake engines with
spring-loaded push rods. As a result, valve yoke
guide pins at the inlet and non-brake exhaust
valve locations have been eliminated from the
cylinder heads.
For pinless yokes at the exhaust positions of
non-brake engines, the spring-loaded push rods
are mandatory.
The pinless yoke is self-leveling in operation and
does not have a yoke leveling adjustment screw.
Inlet and non-brake exhaust valve lash
adjustments are performed in the normal manner
with the rocker arm adjusting screw. For the
engine brake exhaust valves, it is still necessary
to adjust the valve yoke first, then the rocker arm
lash.
The bottom of the valve yoke that bridges the two
valves has a round hole and an elongated hole
that fit over the valve stems. The nose of the yoke
with the elongated hole has two notches in the
casting. When installing the pinless yokes, it is
important that the end of the yoke with the two
notches faces away from the valve rocker shaft. If
the yoke is installed incorrectly, the yoke will
contact the rocker arm.
63
Figure 63 — Proper Assembly of the Pinless Valve Yoke
5-111.bk Page 57 Monday, July 10, 2006 2:26 PM
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