GMC 4000 Series Service Manual page 478

GENERAL INFORMATION
Exhaust system configurations vary according
to engine type and model designation. In general,
all exhaust system connections are of split-joint
coupled design secured with clamp bolts. Flexible
hangers are used to reduce noise transfer to body
and to relieve concentrated loads on exhaust sy s­
tem components.
In general, mufflers are of heavy duty con­
struction designed for optimum quieting efficiency,
reduced exhaust back pressure, and long life due
to use of aluminized tubes and baffles.
MAINTENANCE
EXHAUST RESTRICTION AND LEAKS
Exhaust system should be inspected periodic­
ally for restrictions and leaks. Restrictions such
as kinked or crimped pipes result in excessive
back pressure which can lead to increased fuel
consumption, power lo ss, and possible damage to
engine combustion chamber components. Exhaust
leaks are commonly the result of loose clamp bolts,
defective exhaust pipe to manifold packing, cor­
roded pipes, or a punctured muffler. In addition to
objectionable noise, a leaking exhaust system could
allow toxic gases to enter cab.
Damaged or corroded exhaust system com­
ponents should be replaced without delay. If it is
G M C S E R V I C E M A N U A L
SECTION 8B
£ * J t a u it S u it e m
absolutely necessary to operate vehicle when an
exhaust leak exists, use extreme caution and keep
cab well ventilated.
EXHAUST SYSTEM ALIGNMENT
m iffler or tail pipe, care should be taken to prop­
erly position components in relation to each other.
Particular care should be given to the installation
of the exhaust pipe and crossover pipe assembly
on "V" engines equipped with single exhaust system .
tem are frequently the cause of annoying noises
and rattles due to improper clearances. Therefore,
leave all clamp bolts and muffler strap bolts loose
temporarily until the entire system has been in­
spected to determine if there is adequate clearance
between exhaust components and frame members.
The weight of the exhaust system should be prop­
erly distributed on all supporting brackets and
hangers. If the load is not properly balanced, re­
position pipes at connecting joints to relieve any
concentrated loads. After adjusting hangers, align­
ing pipes, and repositioning muffler, check entire
system for adequate clearance and then tighten all
clamps, working from front to rear. Start engine
and inspect all connections for leakage.
fold, always use new packings and nuts. Be sure
to clean manifold stud threads with a wire brush
before installing new nuts.
CAUTION
If a gasoline engine is operated with a
faulty exhaust system, poisonous (carbon
monoxide) gas may enter cab and cause
serious or fatal injury to personnel. C a r­
bon monoxide may or may not have a de­
tectable odor, and is tasteless and color­
less. In the presence of carbon monoxide,
physical symptoms such as headache, eye
smarting and/or drowsiness may be ex­
perienced.
During installation of a new exhaust pipe,
Incorrectly assembled parts of exhaust s y s­
NOTE: When installing exhaust pipe to mani­
Sec. 8B
Page 467