LeSabre V6-231 3.8L VIN L SFI (1992)
Lifter / Lash Adjuster: Description and Operation
DESCRIPTION AND OPERATION
Hydraulic roller valve lifters and tubular pushrods are used to operate overhead rocker arms and valves of both banks of cylinders from a single
camshaft. This system requires no lash adjustment at time of assembly or in service. Operation of hydraulic valve lifters is described below.
In addition to its normal function of a cam follower, each hydraulic valve lifter also serves as an automatic adjuster which maintains zero lash in
the valve train under all operating conditions. By eliminating all lash in the valve train and also providing a cushion of oil to absorb operating
shocks, the hydraulic valve lifter promotes quiet valve operation. It also eliminates the need for periodic valve adjustment to compensate for wear
of parts.
OIL SUPPLY
Oil is supplied to the lifter through a hole in the side of the lifter body which indexes with a groove and hole in the lifter plunger. Oil is then
metered past the oil metering valve in the lifter, through the pushrods to the rocker arms.
PLUNGER OPERATION
When the lifter begins to move up the cam lobe, the check ball is held against its seat in the plunger by the check ball spring which traps the oil in
the base of the lifter body below the plunger. The plunger and lifter body then raise as a unit, pushing up the pushrod to open the valve. The force
of the valve spring which is exerted on the plunger through the rocker arm and pushrod causes a slight amount of leakage between the plunger and
lifter body.
This allows a slow escape of trapped oil in the base of the lifter body. As the lifter rolls down the other side of the cam lobe and reaches the base
circle or "valve closed" position, the plunger spring quickly moves the plunger back (up) to its original position. This movement causes the check
ball to open against the ball spring and oil from within the plunger is drawn into the base of the lifter. This restores the lifter to zero lash.
