Spark Plug Removal; Cylinder Compression Test; Ignition System S E R V I C - Chevrolet 70 Series 1970 Service Manual

GASOLINE ENGINES 6A-4
INTRODUCTION
Engine tune-up c o n sists of diagnosis, and the
required preventive m aintenance perform ed at
regular in tervals to provide maximum perform ­
ance and economy.
A sy stem a tic procedure
when tuning an engine. The operations should be
perform ed in sequence suggested by "Tune-up
Sequence Index on p revious page.
NOTE: When perform ing work where electrica l
term in als could be accidentally grounded, discon­
nect the battery cab les so no damage to c ir c u its
w ill resu lt.
ENGINE TUNE-UP

SPARK PLUG REMOVAL

1. Clean a ll foreign m atter away from around
spark plugs and w iring using com pressed a ir. D is ­
connect spark plug w ir e s, and loosen each spark
plug one turn.
2. Reconnect plug w ir e s, start engine and a c ­
cele r a te to approxim ately 1,000 rpm. T his is done
Figure 2—Cylinder Numbering and Spark
Plug Wire Locations for V6 Engine
to blow away lo o s e dirt p a r ticle s and carbon. F a il­
u re to do this in c r e a se s the p o ssib ility of foreign
m aterial lodging under v a lv es, with resultant fa lse
readings and p o ssib le valve damage.
3. Stop engine, disconnect plug w ires and r e ­
m ove spark plugs and g ask ets.

CYLINDER COMPRESSION TEST

1. With carburetor choke and throttle in w ide-
open position , operate sta rter with rem ote control
sw itch.
must be follow ed
crank engine through at le a st four com pression
stro k es to obtain highest p o ssib le reading.
and record each reading.
inject about one tablespoon of engine oil into com ­
bustion cham ber through spark plug hole. Crank
engine to spread o il on cylinder w alls, then r e ­
check com pression with gauge.
e ssa r ily reach norm al p ressu re, worn piston rings
are indicated.
oil to cylinder, it is probable that valves are not
properly seating p ossib ly due to sticking in guides,
or burned valves or se a ts.
norm al com p ression , and injecting oil into cylin ­
ders does not in crea se com p ression, the cause
may be a head gasket leak between the cylin d ers.
T his condition could be cau se of coolant leaking
into cylin d ers.
p r essio n cannot be tuned to givepeakperform ance;
th erefore, it is important to make n e cessa r y co r­
rection s before proceeding with tune-up operations.
SERVICE AND INSTALL SPARK PLUGS
glazed, broken, or b listered p orcelain s and burned
electrod es.
siv e type clean er such as sand b laster to thorough­
ly clean spark plugs. F ile end of center electrod e
flat.
When replacing spark plugs, u se the type of plugs
liste d in "Engine Tune-up Specifications."
torque wrench and sp ecia l spark plug socket
w rench. C orrect torque for spark plug installation
is 32 foot-pounds.
IGNITION SYSTEM SERVICE
a c c e s s to ignition distributor, spark plug w ires
and coil.
CAUTION: When using remote switch
to operate s ta rte r, the p rim a ry w ire must
be disconnected from coil negative te rm ­
inal and ignition switch must be turned on.
F ailu re to do this will result in damaged
grounding c ircu it in ignition switch.
2. Starting with com p ression gauge at zero,
3. Make com pression check at each cylinder
4. If som e cylind ers have low com pression,
a. If com p ression is higher but does not n ec­
b. If com p ression is not im proved by adding
c. If two adjacent cylinders have low er than
NOTE: An engine with low or uneven com ­
1. Inspect all sp a rk p lu g s carefully. Look for
2. If sp a rk p lu g s are serv icea b le, u se an abra­
3. Adjust spark plug gaps to sp ecification s.
4. T est spark plugs with spark plug te ste r .
5. Install spark plugs using new gasket. U se
1. Remove equipment as required to provide
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL