Checking Compression; Service & Install Spark Plugs; Spark Plug Detail; Service Ignition System - Chevrolet 10 1971 Series Chassis Service Manual

ENGINE 6-2
Fig. 1— Checking Compression
1. Remove air cleaner and block throttle and choke in
wide open position.
2. Hook up starter remote control cable and insert
compression gauge firmly in spark plug port.
Whenever the engine is cranked
CAUTION:
remotely at the starter, with a special jumper
cable or other means, the distributor primary
lead must be disconnected from the negative
post on the coil and the ignition switch must be
in the " ON" position.
result in a damaged grounding circuit in the
ignition switch.
3. Crank engine through at least four compression
strokes to obtain highest possible reading.
4. Check and record compression of each cylinder.
5. If one or more cylinders read low or uneven, inject
about a tablespoon of engine oil on top of pistons
in low reading cylinders
port). Crank engine several times and recheck
compression.
• If compression comes up but does not necessarily
reach normal, rings are worn.
• If compression does not improve, valves are
burned, sticking or not seating properly.
• If two adjacent cylinders indicate low compression
and injecting oil does not increase compression,
the cause may be a head gasket leak between the
cylinders. Engine coolant and/or oil in cylinders
could result from this defect.
If a weak cylinder cannot be located
NOTE:
with the compression check, see " Cylinder Bal­
ance Test" under " Additional Checks and Ad­
justments" in this section.
Service & Install Spark Plugs (Fig. 2)
1. Inspect each plug individually for badly worn elec­
trodes, glazed, broken or blistered porcelains and
replace plugs where necessary.
2. Clean serviceable spark plugs thoroughly, using an
abrasive-type cleaner such as sand blast. File the
center electrode flat.
Failure to do this will
(through spark plug
3. Inspect each spark plug for make and heat range.
All plugs must be of the same make and number.
4. Adjust spark plug gaps to specifications using a
round feeler gauge.
Never bend the center electrode to
CAUTION:
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
installing plugs. Corrosion deposits can be removed
with a 14 mm. x 1.25 SAE spark plug tap (available
through local jobbers) or by using a small wire
brush in an electric drill.
catch chips.)
Use extreme care when using tap to
CAUTION:
prevent cross threading. Also crank engine sev­
eral times to blow out any material dislodged
during cleaning operation.
7. Install spark plugs and torque to specifications.
The following are some of the greatest
NOTE:
causes of unsatisfactory spark plug performance.
• Installation of plugs with insufficient torque to
fully seato
• Installation of the plugs using excessive torque
which changes gap settings.
• Installation of plugs on dirty seat.
• Installation of plugs to corroded spark plug hole
threads.
8. Connect spark plug wiring.

Service Ignition System

1. Remove distributor cap, clean cap and inspect for
cracks, carbon tracks and burned or corroded ter­
minals. Replace cap where necessary (fig. 3).
INSULATOR CRACKS
OFTEN O C C U R HERE
CENTER ELECTRODE
FILE FLAT W H E N
ADJU STIN G G A P -
D O NO T BEND!
Fig. 2— Spark Plug Detail
(Use grease on tap to
PORCELAIN
INSULATOR
SHELL
(PROPER GAP)
SIDE ELECTRODE
(BEND TO ADJUST G AP)
10-30 CHEVROLET TRUCK SERVICE MANUAL