Chevrolet 10 Series 1970 Service Manual page 351

c. Back out adjusting nut until lash is fe lt at the
push rod then turn in adjusting nut until a ll lash
is rem oved. T h is can be determ ined by checking
push rod side play w hile turning adjusting nut
(fig . 2V). When play has been rem oved , turn
adjusting nut in one full additional turn (to center
lift e r plunger).
d. Crank the engine on revolution until the pointer
" O " m ark and torsion al dam per m ark a re again
in alignm ent. T his is number 6 firin g position.
W ith the engine in this position the follow ing
va lves may be adjusted.
Exhaust - 2, 5, 6, 7
Intake
4. Install ro ck e r arm c o v e rs as outlined.
5. Adjust carbu retor id le speed and m ixture.
V a lv e Lifters
H ydraulic va lve lift e r s v e r y seldom requ ire attention.
T h e lifte r s are ex tre m e ly
m ents a re not n ecessary, and s e rv ic in g of the lifte r s
re q u ire s only that ca re and clean lin ess be e x e rcised in
the handling o f parts.
Locating Noisy Lifters
L ocate a noisy va lve lift e r by using a piece of garden
hose approxim ately four fee t in length. P la c e one end
o f the hose near the end of each intake and exhaust valve
with the other end of the hose to the ear. In this manner,
the sound is lo c a lize d making it easy to determ ine which
lift e r is at fault.
Another method is to place a fin g er on the face o f the
v a lv e spring retain er. If the lift e r
p ro p e rly , a distinct shock w ill be fe lt when the valve
retu rn s to its seat.
The gen eral types o f va lv e lift e r noise are as follow s:
1. Hard Rapping N o is e --U s u a lly caused by the plunger
becom ing tight in the b ore o f the lift e r body to such
an extent that the return spring can no lon ger push
the plunger back up to working position. Prob ab le
causes are:
a. E x cessive varnish
abnorm al stickiness.
b. G alling o r "p ic k -u p between plunger and bore of
lift e r body, usually caused by an ab rasive piece
o f d irt o r m etal w edging between plunger and
lift e r body.
2. M oderate Rapping N o is e --P r o b a b le causes are:
a. E x ces sive ly high leakdown rate.
b. Leaky check va lv e seat.
c. Im proper adjustment.
3. G eneral N oise Throughout the V alve T r a in --T h is
w ill, in alm ost a ll cases, be a definite indication of
insufficient o il supply, o r im p rop er adjustment.
4. Interm ittent C lic k in g --P ro b a b le causes are:
a* A m icro sco p ic p iece o f d irt m om entarily caught
between b all seat and check va lve ball.
b. In ra re cases, the b all its e lf may be out-of-round
o r have a fla t spot.
c. Im proper adjustment.
In m ost cases w here noise exists in one o r m ore lifte r s
a ll lift e r units should be rem oved, disassem bled, cleaned
in a solvent, reassem b led , and rein sta lled in the engine.
If d irt, corrosion , carbon, etc. is shown to exist in one
- 3, 4, 6, 8
sim ple in design, readju st­
is not functioning
o r carbon deposit causing
F ig . 2 V —V a lv e A d justm ent
unit, it m ore lik e ly exists in a ll the units, thus it would
only be a m atter o f tim e b efo re all lifte r s caused trouble.
Removal
1. Rem ove intake m anifold as outlined.
R em ove valve m echanism as outlined.
2 .
R em ove va lve lifte r s .
3 .
NOTE: P la c e va lve lifte r s
may be rein sta lled in the same location.
Installation
1. Install va lve lifte r s .
NOTE: W henever new va lve lift e r s a re being
installed, polish lift e r
em ery paper and coat foot o f valve lifte r s with
" M olykote" o r its equivalent.
Install intake m anifold as outlined.
2 .
Install and adjust va lve mechanism as outlined.
3 .
V a lv e Stem O il Seal a n d /o r V a lv e Spring
Replacement
1. R em ove ro ck er arm cover as outlined.
R em ove spark plug, rock er arm and push rod on the
2 .
cy lin d er(s) to be se rvic ed .
Apply com pressed a ir to the spark plug hole to hold
3 .
the v a lv es in place.
NOTE: A tool to apply a ir to the cylin d er is
available through loca l jobbers o r may be fab­
ricated using an A C -46N
equivalent. T h is w ill make the tool u n iversal fo r
a ll C h evrolet engines. Chisel the spark plug as
shown, then d riv e the porcela in out o f the plug
by tapping the center electrod e against a hard
block. Using a pipe tap, cut threads in the
3 / 8 "
rem aining portion o f the spark plug and a ssem ­
ble as shown (fig .
3 V ) .
ENGINE 6-29
in a rack so they
fir s t with #600 w et/dry
spark plug o r its
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