Test Compression; Service & Install Spark Plugs; Checking Compression; Spark Plug Detail - Chevrolet CHEVY VAN G10 SERIES Service Manual

ENG INE 6-2
Fig. 1—C hecking C om pression
TEST COMPRESSION (FIG . 1)
The com pression check is im p o rtan t because an engine w ith
low or uneven com pression cannot be tuned successfully. It is
essential th a t im proper com pression be corrected before p ro ­
ceeding w ith the engine tu n e up.
1. Remove air cleaner and block th ro ttle and choke in wide
open position.
2. H ook up starter rem ote co ntrol cable and insert com pres­
sion gauge firm ly in spark plug port.
C A U T IO N : Whenever the engine is cranked re­
motely at the starter, w ith a special jum per cable or
other means, the distributor primary lead must be
disconnected from the negative post on the coil.
3. C rank engine th rou gh at least four com pression strokes
to ob tain highest possible reading.
4. Check and record com pression o f each cylinder.
5. I f one or m ore cylinders read low or uneven, inject about
a tablespoon o f engine oil on top o f pistons in low
reading cylinders (throu gh spark plug p o rt). C rank engine
several tim es and recheck com pression.
• If com pression com es up b u t does no t necessarily
reach norm al, rings are w orn.
• If com pression does n o t im prove, valves are burnt,
sticking or n ot seating properly.
• If tw o adjacent cylinders indicate low com pression
and injecting oil does n o t increase com pression, the
cause m ay be a head gasket leak betw een the
cylinders. Engine coolant and/or oil in cylinders
could result from this defect.
N O T E : If a weak cylinder cannot be located w ith
the compression check, see "C ylinder Balance test"
under "A d d itio nal Ciiecks and Adjustm ents" in this
section.
SERVICE & INSTALL SPARK PLUGS (FIG . 2)
1. Inspect each plug individually for badly w orn electrodes,
glazed, broken or blistered porcelains and replace plugs
w here necessary.
2. Clean serviceable spark plugs thoroughly, using an
abrasive-type cleaner such as sand blast. File the center
electrode flat.
3. Inspect each spark plug for make and heat range. All
plugs m ust be o f the same make and num ber.
4. A djust spark plug gaps to specifications using a round
feeler gauge.
C A U T IO N : Never bend the center electrode to
adjust gap. Always adjust by bending ground or side
electrode.
5. If available, test plugs with a spark plug tester.
6
. Inspect spark plug hole threads and clean before in­
stalling plugs. Corrosion deposits can be rem oved w ith a
14 m m . x 1.25 SAE spark plug tap (available through
local jobbers) or by using a small wire brush in an electric
drill. (Use grease on tap to catch chips.)
C A U T IO N : Use exptrem e care when using tap to
prevent cross threading. Also crank engine several
times to blow out any material dislodged during
cleaning operation.
7. Install spark plugs and torque to specifications.
N O T E : Tiie following are some of the greatest
causes of unsatisfactory spark plug performance.
• Installation o f plugs w ith insufficient torque to
fully seat.
• Installation o f the plugs using excessive torque
w hich changes gap settings.
• Installation o f plugs on dirty seat.
C H E V Y V A N SHOP M A N U A L