Buick LeSabre 1965 Service Manual page 36

2 - 1 4 ENGINE DESCRIPTION
ENGINE
ROCKER
ARM
PUSH
ROD SEAT
Figure 2-8—Valve Rocker Arm
speed range. Inlet valve heads
are 1-7/8" and exhaust valve
heads are 1-1/2" in diameter.
Valves and rocker arms are pro-
tected by a cover which seats
against a raised horizontal sur-
face on each cylinder head, and
a cork gasket insures against oil
leaks.
f. Hydraulic Valve Lifters
In addition to its normal function
of a cam follower, each hydraulic
valve lifter also serves as an
automatic adjuster which main-
tains zero lash in the valve oper-
ating linkage under all operating
conditions. By eliminating all lash
in the operating linkage and also
providing a cushion of oil to
absorb operating shocks, the hy-
draulic valve l i f t e r promotes
quiet v a l v e operation. It also
eliminates the need for periodic
valve adjustment to compensate
for wear of parts.
As shown in Figure 2^9, all parts
of a hydraulic lifter are housed
in the body, which is the cam
f o l l o w e r . The body and the
plunger are ground to very close
limits, then a plunger is selec-
tively fitted to each body to as-
sure free movement with very
little clearance. The push rod
seat is free to move with the
plunger in the body and, as its
name i m p l i e s , it provides a
spherical s e a t to support the
lower end of the push rod.
SNAP RING
ROD SEAT
OIL INLETS
PLUNGER
FEED HOLE
BALL RETAINER
PLUNGER
SPRING
LIFTER BODY
NOTE
BRAZED
CAP
Figure 2-9—Hydraulic Valve Lifter,
Sectional View
The plunger and seat are pressed
toward the upper end of the lifter
body by a coil spring which also
holds a check ball r e t a i n e r
against the l o w e r end of the
plunger. When lifter is out of
engine a spring wire retainer
holds all parts in the body. The
ball retainer holds a s p r i n g
loaded check ball in position over
the lower end of a feed hole in
the plunger. See Figure 2-9.
When the valve lifter is installed
in engine the push rod holds the
seat and plunger downward clear
of the plunger retainer at all
times. The plunger spring then
presses the lifter body down
against the camshaft and presses
the plunger and seat up against
the push rod with an eight pound
load, which is enough to take up
all lash clearances between parts
in the valve l i n k a g e without
affecting positive seating of the
valve.
Oil is fed to all lifters through
galleries in the crankcase, as
described in paragraph 2-6. Oil
enters each lifter through grooves
and oil holes in the lifter body
and plunger, and flows down into
the chamber below the plunger
through the feed hole and around
the check ball. The first few
cycles of operation a f t e r the
engine is started forces out all
air and c o m p l e t e l y fills the
plunger and lower chamber of
each lifter with oil.
At the start of a cycle of valve
operation, the lifter body rests
on the camshaft base circle. The
plunger spring holds all l a s h
c l e a r a n c e s * out of the valve
linkage.
As the rotating camshaft starts
raising valve lifter body, oil in
the lower chamber and the check
ball spring firmly seats the check
ball against the plunger to prevent
appreciable loss of oil from the
chamber. The lifting force against
the body is then transmitted
through the entrapped oil to the
check ball and plunger and push
rod seat move upward with the
body to operate the linkage which
opens the engine valve.
As the camshaft rotates further
to close the engine valve, the
valve spring forces the linkage
and lifter to follow the cam down.
When the engine valve seats, the
linkage parts and lifter plunger
stop but the plunger spring forces
the body to follow the cam down-
ward .002" to .003" until it again
rests on the camshaft base circle.
Oil pressure against the check
ball from the lower chamber
ceases when the plunger stops
and allows passage of oil past the
check ball into the lower chamber
to replace the slight amount of
oil lost by "leak-down' \
During the valve opening and
closing operation a very slight
amount of oil escapes through the
clearance between plunger and
body and returns to the crank-
case. This slight loss of o i l
(called "leak-down") is beneficial
in providing a gradual change of
oil in the lifter, since fresh oil
enters the lower chamber when