DESCRIPTION & OPERATION
Page 27
Camshaft
The large diameter of the camshaft (Figure 24)
provides the strength necessary for actuating the
unit pumps. In addition to the inlet and exhaust
valve lobes, lobes have been added to drive the
unit pumps. The camshaft also has more
aggressive intake and exhaust cam profiles for
improved fuel economy and emissions. A bump
in the exhaust cam profile provides timing for
engine brake operation.
The camshaft has induction-hardened journals
and lobes. This process produces a pronounced
heat discoloration mark approximately 3/8-inch
wide, around the front and rear faces of each
journal and lobe.
As an additional aid in reducing cam bushing
temperature, a groove has been added to the No.
4 journal of current-production camshafts. This
groove was not included on early-production
units. Adding the groove to the camshaft journal
has not resulted in a change to the camshaft part
number.
24
Figure 24 — Camshaft
Valve Train
The valve train accommodates the aggressive
cam profiles. Roller lifters and roller followers or
“tappets” (Figure 25) are used to actuate the
valves and unit pumps, respectively. The roller
lifters handle aggressive cam profiles better and
have increased load-carrying capability.
25
Figure 25 — Roller Lifters
VALVES
The stem tip of the valve has grooves to identify
the valve as intake or exhaust. The exhaust seat
face is 30 degrees, whereas the inlet valve seat is
20 degrees.
5_106_00.bk Page 27 Friday, August 4, 2000 11:17 AM
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