Pontiac FIREBIRD 1972 Service Manual page 525

SIX CYLINDER ENGINE 6-13
Fig. 6 - 1 0 Valve Train
HYDRAULIC VALVE LIFTERS
Hydraulic valve lifters are used to keep all parts of the
valve train in constant contact.
The hydraulic lifter assembly (Fig. 6- 1 1 and 6- 12) in-
cludes: the cast iron body which rides in the cylinder block
boss, the plunger, push rod seat, metering valve, plunger
spring, ball check valve and spring, ball check valve re-
tainer, and retainer ring.
The hydraulic valve lifter functions as follows: when the
lifter is riding on the low point of the cam, the plunger
spring keeps the plunger and push rod seat in contact with
the push rod.
When the lifter body begins to ride up the cam lobe, the
ball check valve cuts off the transfer of oil from the reser-
voir below the plunger. The plunger and lifter body then
rise as a unit, pushing up the push rod and opening the
valve.
As the lifter body rides down the other side of the cam,
the plunger follows with it until the valve closes. The lifter
body continues to follow the cam to its low point, but the
plunger spring keeps the plunger in contact with the push
rod. The ball check valve will then move off its seat and
the lifter reservoir will remain full.
I
PUSH I
ROD
- 1
ROCKER
FEED
/
METERING VALVE
LIFTER
. q
BODY
RETAINER
RlNG
BALL CHECK
'
VALVE
.BALL CHECK
VALVE
RETAINER
PLUNGER
SPRING
- -
Fig. 6 - 1 1 Valve Lifter
During operation a small amount of oil leaks out of the
lifter between the plunger and body. A controlled amount
of leakage is important to provide continuous adjustment
of the plunger position within the lifter. This leakage is
called "leak-down" and must be within certain limits to
provide correct operation (See "Valve Lifter
-
Test Leak-
Down Rate").
Oil is supplied to the lifter by the cylinder block oil gallery
to replace that lost through leak-down. The annular
groove around the outside of the lifter body indexes with
the passage drilled from the gallery to the lifter boss. Oil
then enters the lifter from this groove and passes into the
plunger cavity. From the plunger cavity, oil under pres-
sure is also fed up the push rod to lubricate the friction
area between the uvver end of the push rod and the rocker
arm and other upper valve train contact points.
BODY
BALL CHE(
VALVE RETA
1
d h
f
PLUNGER
PLUNGER
SPRING
ROD
AT
ROCKER FEED / R E T A I N E R
METERING VALVE
RlNG
Fig. 6 - 1 2 Hydraulic Valve Lifter
-
Exploded V i e w