Chevrolet 1977 light duty truck, Руководство по обслуживанию

Страница: 456 / 861

Fig. 6A-12--Valve A djustm ent
Fig. 6A -13-C om pressing Valve Spring
1. R em ove rocker arm cover as previously
outlined.
2. Remove spark plug, rocker arm and push rod on
the cylinder(s) to be serviced.
3. Install air line a d a p te r Tool J-23590 to spark
plug port and apply compressed air to hold the valves in
place.
4. U sing Tool J-5892 to compress the valve spring,
rem ove the valve locks, valve cap, valve shield and valve
spring and d a m p e r (fig. 6A-13).
5. Remove the valve stem oil seal.
6. To replace, set the valve spring, valve shield and
valve can in place. Com press the spring with Tool J-5892
and install oil seal in the lower groove o f the stem,
m ak in g sure the seal is flat and not twisted.
N O T E : A light coat o f oil on the seal will help
prevent twisting.
7. Install the valve locks and release the com pres­
sor tool, m aking sure the locks seat properly in the upper
groove o f the valve stem.
NOTE: G rease may be used to hold the locks in
place while releasing the compressor tool.
8. Install spark plug, and torque to 15 lb. ft.
9. Install and adjust valve mechanism as previously
outlined.
VALVE LIFTERS
Hydraulic valve lifters very seldom require atten ­
tion. The lifters are extremely simple in design.
R eadjustm ents are not necessary, and servicing o f the
lifters requires only that care and cleanliness be
exercised in the handling o f parts.
Locating Noisy Lifters
Locate a noisy valve lifter by using a piece of
garden hose approxim ately four feet in length. Place one
end o f the hose near the end o f each intake and exhaust
valve with the other end o f the hose to the ear. In this
m a n n e r the sound is localized, m aking it easy to
d eterm ine which lifter is at fault.
A n o th e r m ethod is to place a finger on the face o f
the valve spring retainer. If the lifter is not functioning
properly, a distinct shock will be felt w hen the valve
returns to its seat.
T he general types o f valve lifter noise are as
follows:
1. Hard R a p p in g Noise - Usually caused by the
plunger becoming tight in the bore o f the lifter body to
such an extent t h a l j h e return spring can no longer push
the plunger back up to w orking position. P robable causes
are:
a. Excessive varnish or c a rb o n deposit causing
ab n o rm al stickiness.
b. G alling or "p ick u p " between plunger and
bore o f lifter body, usually caused by an abrasive piece
o f dirt or metal w edging between plunger and lifter
body.
2. M oderate R ap p in g Noise - Probable causes are:
a. Excessively high leakdown rate.
b. Leaky check valve seat.
c. Im proper adjustment.
3. G eneral Noise T hroughout the Valve T rain -
This will, in most cases, be caused by either insufficient
oil supply or im p ro p e r adjustment.
4. Interm ittent Clicking Probable causes are:
a. A microscopic piece o f dirt m om entarily
caught between ball seat and check valve ball.
b. In rare cases, the ball itself m ay be out-of­
round or have a flat spot.
c. Im proper adjustm ent.
J - 5 8 9 2
L ___
J - 2 3 5 9 0