Chevrolet 10 Series 1970 Service Manual page 324

ENGINE 6-2
F ig . 1—C h e c k in g Compression
1. R em ove a ir clean er and block throttle and choke in
wide open position.
2. Hook up sta rte r rem ote control cable and insert
compression- gauge fir m ly in spark plug port.
CAUTION:
W henever
rem o te ly at the s ta rte r, with a special jum per
cable o r other means, the distributor p rim a ry
lead must be disconnected from the negative
post on the c oil and the ignition switch must be
in the " O N " position.
resu lt in a damaged grounding circu it in the
ignition sw itch.
3. Crank engine through
strok es to obtain highest p ossib le reading.
4. Check and re c o rd com pression o f each cylin der.
5. If one o r m ore cylin d ers read low o r uneven, inject
about a tablespoon o f engine o il on top o f pistons
in low reading cylin d ers
p ort). Crank engine
com pression.
• If com pression com es up but does not n e cessa rily
reach norm al, rings a re worn.
• If com pression does
burnt, sticking or not seating p rop erly.
• If two adjacent cylin d ers indicate low com pression
and injecting o il does not in crease com pression,
the cause may be a head gasket leak between the
cylin ders. Engine coolant and/or o il in cylin ders
could resu lt fro m this defect.
NOTE:
If a weak cylin d er cannot be located
with the com pression check, see " C ylin der B a l­
ance T e s t" under "A d d itio n a l Checks and A d ­
justm ents" in this section.
Service & Install Spark Plugs (Fig. 2)
1. Inspect each plug individually fo r badly worn e le c ­
trodes, glazed , broken o r b lis tere d p o rcelain s and
replace plugs where n ecessary.
2. Clean serv ic e a b le spark plugs thoroughly, using an
ab ra sive-typ e clean er such as sand blast.
cen ter electrod e flat.
the engine is cranked
F ailu re to do this w ill
at least four com pression
(through spark plug
s e v e ra l tim es and recheck
not im prove, v a lv es a re
F ile the
3. Inspect each spark plug for make and heat range.
A ll plugs must be o f the same make and number.
4. Adjust spark plug gaps to specification s using a
round fe e le r gauge.
CAUTION: N ever bend the center electrod e to
adjust gap. Alw ays adjust by bending ground or
side e le c tro d e .
5. If available, test plugs with a spark plug tester.
6. Inspect spark plug hole threads and clean b efore
installing plugs. C orrosion deposits can be rem oved
with a 14 mm. x 1.25 SAE spark plug tap (available
through local jobbers) o r by using a sm all w ire
brush in an e le c tr ic d r ill.
catch chips.)
CAUTIO N: Use extrem e ca re when using tap to
preven t cro s s threading. A ls o crank engine s e v ­
era l tim es to blow out any m a teria l dislodged
during cleaning operation.
7. Install spark plugs
NOTE: The follow ing a re som e o f the grea test
causes o f unsatisfactory spark plug p erform an ce.
• Installation of plugs with insufficient torque to
fully seat.
• Installation o f the plugs using exc es sive torque
which changes gap settings,,
• Installation of plugs on dirty seat.
• Installation o f plugs to corroded spark plug hole
threads.
8. Connect spark plug w iring.
Service Ignition System
1. Rem ove distributor cap, clean cap and inspect fo r
cracks, carbon tracks and burned or corroded t e r ­
m inals. R eplace cap where n ecessary (fig. 3).
F ig . 2 —Spark Plug D e ta il
(Use grea se on tap to
and torque to specification s.
CHEVROLET TRUCK SERVICE MANUAL