GMC 4000 Series Service Manual page 303

Sec. 6B
Page 292
TORO-FLOW DIESEL ENGINE
Before installing a fuel injection nozzle, use fine
brass-bristled brush (fig. 3) to clean nozzle tip.
The compression pressure in any one cylinder
should be not le ss than 500 psi at 625 rpm. In ad­
dition, the variation in compression pressures
between cylinders of the engine must not exceed
30 psi at 625 rpm.
8. Low cylinder pressures may result from
any one of several causes:
a. Piston rings may be worn, stuck, or broken.
b. Compression may be escaping past valves,
or cylinder head gasket may be defective.
ENGINE TUNE-UP
BATTERY AND BATTERY CABLE SERVICE
1. Using battery hydrometer, check specific
gravity of storage battery electrolyte in each cell.
Gravity reading below 1.230 (corrected to 80 F.)
indicates insufficient charge.
2. Use a voltmeter to check cranking voltage.
Be sure to place engine control in stop position to
prevent engine from starting during test.
3. With voltmeter connected between solenoid
terminal and ground, operate starter. Voltage of
9 volts or more when starter is cranking engine
indicates that battery, and circuit to solenoid is
satisfactory. If voltage reading is less than 9 volts
when engine is being cranked, or if cranking speed
is low; a weak battery, defective starter switch,
or excessive resistance in starting circuit exists.
NOTE: If, when making check of cranking volt­
age, it is noted that cranking speed is uneven; this
is an indication of uneven cylinder compression,
defective starter or starter drive.
Figure 4 — A d ju stin g E ngine Id lin g Speed
G M C S E R V I C E M A N U A L
w ise defective battery cables and/or wiring are
found, the defects must be corrected to insure good
engine performance.
of being defective, refer to appropriate coverage
in ENGINE ELECTRICAL (SEC. 6Y) of this manual
for method of diagnosing battery deficiencies.
this manual for procedure required to check per­
formance of charging circuit units.
DRIVE BELT ADJUSTMENT
old belts, use tension gauge to provide correct
tension.
COOLING SYSTEM INSPECTION
in this manual for arrangement of cooling system
units and for inspection and required maintenance
procedures.
CYLINDER HEAD BOLTS
require retightening at tune-up intervals. When
necessary to tighten cylinder head bolts, refer to
"Cylinder Head Replacement" covered later in this
section, for bolt tightening sequence.
MANIFOLD BOLTS
for proper torque and be sure end bolts have wash­
ers installed as shown in figure 8.
VALVE CLEARANCE
approximately 160° is reached, then remove rocker
arm covers.
set exhaust valves to 0.018-inch clearance, and set
intake valve clearance to 0.010-inch.
gaskets and tighten cover screw s firmly (3 to 5
foot-pounds).
FUEL SYSTEM INSPECTION
and return line between engine and fuel tank, for
evidence of leakage.
4. In cases where loose, corroded, or other­
5. If battery is weak or shows other evidence
Refer to ENGINE ELECTRICAL (SEC. 6Y) in
When installing new drive belts or adjusting
CAUTION: Adjusting drive belts too
tightly will impose too great a load on
bearings in the driven units. Slipping will
occur if drive belts are not adjusted tight
enough. Belt life will be shortened if belts
are not properly tightened.
Refer to ENGINE COOLING SYSTEM (SEC. 6K)
Normally the cylinder head bolts should not
At tune-up intervals, check all manifold bolts
1. Run engine until operating temperature of
2. Using feeler gauges and box-end wrench,
3. Reinstall rocker arm covers with new cover
1. Inspect all fuel lines, both the supply line