S e c . 6A
P a g e 11
SECTION 6A
Q a d -a lln e . C n c u n e A ,
The inform ation pertinent to truck m od els co v ered by th is Supple
m ent i s the sa m e as given in S e r v ic e Manual S T -3 3 1 -7 1 (pages 6A -1
thru 6A -34) with the follow ing ex cep tio n s an d /o r additions:
ENGINE MAINTENANCE
Inspection, adjustm ent or rep lacem en t of e m is
sio n control related com ponents m ust be perform ed
on a tim e or m ilea g e b a sis as indicated. Good
judgment is required in replacem ent of p arts in
th ose c a s e s w here the accum ulated m ileage is
su b stan tially low er during the sp e cified tim e period.
SERVICING AIR CLEANER
A ir c le a n e r s should be in sp ected and se r v ic e d
every 12,000 m ile s or m ore often under s e v e r e
dust conditions; a lso , w henever dirt is v isib le in
elem en t or o il. R efer to "AIR CLEANERS” (SEC.
6M) of th is supplem ent or S T -331-71 S erv ice
Manual.
IMPORTANT: V eh icle operation under condi
tio n s such a s heavy dust, continuous short tr ip s,
stop and go driving, e tc ., is not con sid ered norm al
u se and th er efo re m ore frequent m aintenance w ill
be required. Such additional m aintenance req u ire
m ents a re included below w here applicable.
T h erm o sta tica lly C ontrolled A ir C leaner
The a ir clea n er should be in sp ected to make
certain that a ll h o ses and ducts a re intact and c o r
re ctly in sta lled . O perational function should be
checked by in specting p osition of valve in a ir intake.
With engine stopped, valve should be open. At
underhood tem perature below 10 0 °F ., with engine
running, valve should be p artially or fully c lo sed .
A s engine underhood tem perature r is e s , the valve
should open.
CHECKING DRIVE BELTS
Fan b elt ten sion on v e h ic le s equipped with
V -b e lts should be adjusted to 120 - 130 pounds on
new b e lts using B T -3 3 -7 3 F B elt T ension Gauge.
U sed drive V -b elts should be adjusted to 80 - 90
pounds. Gauge should be placed at cen ter of the
g re a te st span.
IMPORTANT: A fter a belt has been in op er
ation one hour or approxim ately 50 m ile s, it is
con sid ered u sed . B e lt d r e ssin g can be u sed to ex
tend belt life . When V -b e lts a re worn they should
be rep la ced , as e x c e s s iv e tightening w ill not p r e
vent slippage and can ca u se dam age to b earin gs.
SPARK PLUGS
R eplace spark p lugs at 12,000 m ile in te r v a ls.
U se of leaded fu e ls r e su lts in lead d ep o sits on
spark plugs and can ca u se m isfir in g at m ile a g e s
l e s s than 12,000 m ile s . W here m isfirin g o c c u r s
p rio r to 12,000 m ile s , spark plugs in good condition
can often be cleaned, te ste d and r e in sta lle d in an
engine with acceptable r e s u lts .
ENGINE COMPRESSION
Minimum co m p ressio n record ed in any one
cylin d er should not be l e s s than 70% of h igh est
cy lin d er. For exam ple, if the high est p r e s s u r e in
any one cylinder is 150 lb s ., the lo w est allow able
p r e s s u r e for any other cylin d er would be 105 lb s .
(150 x 70% = 105).
T his te st should be p erform ed to p rovid e r e a
sonable a ssu ra n ce that engine condition i s s u ffic
iently efficien t to prevent leakage of unburned
g a s e s . If a problem e x is ts , have c o r r e c tio n s m ade.
DISTRIBUTOR POINTS, CAM LUBRICATOR
D istributor points should be in sp ected p r io r to
perform an ce of tune-up adjustm ents. B urned or
pitted points m ust be rep laced . P oin ts in good con
dition may be r eu sed after readjustm ent and the
in stallation of a new cam lu b ricator. New p oints
and cam lu b ricator should be in sta lled at le a s t
every 24,000 m ile s .
DISTRIBUTOR CAP
The in terior and e x terio r of the d istrib u tor
cap should be carefu lly in sp ected and clean ed to
prevent m isfirin g and d eterioration .
SPARK PLUG WIRES
Inspect spark plug w ir e s for evidence of ch eck
ing or cracking of ex terio r insulation and a tight
fit in the distributor cap and at the spark p lu g s.
E xterior of w ir e s should be cleaned, any evid en ce
of co r ro sio n on ends rem oved and w ire rep la ced
if d eteriorated .
TIMING, POINTS (DWELL), IDLE SPEED
T h ese adjustm ents m ust be p erform ed a c c u r
a tely , follow ing the sp ecifica tio n s shown on the
lab el under the hood. A djustm ents m ust be m ade
with te s t equipment known to be accu ra te.
