MP7 and MP8 engines utilize pin-less valve yokes at the inlet and exhaust
valves, similar to the pin-less yokes used on previous Mack engines such as
ASET and E-Tech.
The holes on the bottom of the yoke that fit over the valve stem tips are round
on one end and elongated on the other. The yokes are not symmetrical. From the
centerline of the yoke pad, the end with the round hole is shorter than the end
with the elongated hole.
It is extremely important that the valve yokes be installed with the elongated
hole over the outboard valve, away from the camshaft (toward the inlet
manifold). Should the end of the valve yoke with the elongated hole be
installed over the inboard valve (toward the camshaft), contact with the rocker
arm will occur, resulting in a dropped valve and significant engine damage. An
engine failure due to improper valve yoke installation during a field repair is
not warrantable. Refer to the Figure 1, for illustration of proper valve yoke
During rocker shaft removal, reinstallation or repositioning, a valve yoke may
become disengaged from the valve stem tip. If this is not corrected prior to
starting the engine, major engine damage will result. Extra care must be taken
during rocker shaft removal and reinstallation to ensure all yokes are properly
engaged with the valves, and valves must be readjusted whenever the rocker
shaft has been removed and reinstalled for any reason.
Exhaust valve yokes used on Power Leash-equipped engines are of a different
design and not subject to the improper installation issue described above.