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ENGINE DIVISION SERVICE MANUAL
TM 5-4210-230-14&P-1
CHART NO. 18
ENGINE NOISE
Noisy engine operation covers a wide range of
conditions; therefore, to make the most efficient use of
diagnostic aids to correct the condition, an accurate
verification of the symptoms must be made . When the
symptom is identified as to the type and general location
of the noise, proceed to the applicable step outlined
below. It can be seen that many of the steps are based
on similar symptoms and, indeed, may be a matter of
individual interpretation . Therefore, if the most likely
step fails to correct the condition, proceed to the next
most likely step, and so on until the condition is
corrected.
A.
Spark Knock or Pinging
This condition is characterized as being increasingly
more noticeable as engine load increases. That is, at a
given vehicle speed and throttle opening the problem
would generally be more noticeable on a steep grade than
on a level surface. The condition is due to low octane
fuel, excessive spark advance or engine overheating.
If any discrepancies are noted in the following
checks, repair and/or replace as required. Advise owner
of proper octane fuel and verify correct spark plug heat
range. If engine overheating is indicated, perform steps
in CHART 20, check ignition timing and check distributor
mechanical and vacuum advance curve per CTS *
ELECTRICAL section.
B.
Light Clicking (Varies with Engine Speed)
This condition is usually caused by improperly
adjusted,
failed
or
malfunctioning
valve
train
components. Insert feeler gauge between rocker arm and
valve stem tip and/or exert pressure on rocker arm. If
noise
is
eliminated,
adjust
valve
clearance
to
specifications. If condition persists, inspect for worn or
malfunctioning valve train components . If no failure is
detected, check for excessive valve stem-to-valve guide
wear by exerting side pressure on valve stem. If noise is
corrected excessive wear is indicated. If valve is
eliminated as a possible cause, check for accessory
component noise by loosening and/ or removing drive
belts, one at a time, until noise stops . Investigate fuel
pump and/or pump drive as possible cause.
C.
Sharp Rapping (Varies with Engine Speed)
This condition is usually caused by malfunctioning
hydraulic lifter and may be located with the aid of a
stethoscope. If the problem is not corrected, perform
Step B.
D.
Hissing
Inspect vacuum systems for leakage due to loose or
broken
connections
and/or
failed
parts.
Inspect
manifolds for leaks. Perform cylinder compression
and/or leakage tests to identify and isolate cylinder head
gasket leaks. Inspect for carburetor gasket leaks.
E.
Sharp Snapping Noise During Acceleration
Look for arcing from high tension
ignition cables.
F.
Squeaks and/or Squeals
Loosen drive belts, one at a time, to determine if
accessory component or water pump is at fault.
G.
Heavy Squeal During Acceleration
Check for accessory drive belt slippage and adjust
tension or replace as required.
H.
Ringing, Grinding or Combination of Both
Check for loose, bent or improper pulleys. Check for
front end bracket interference between rotating parts and
surrounding components caused by misalignment of
engine, engine components or surrounding components .
Check for worn or damaged water pump or accessory
components by loosening drive belts, one at a time, until
noise stops.
I.
Buzzing or Whistling During Engine Operation
Perform radiator cap functional check and verify
proper cap sealing. If engine overheating is indicated,
perform
engine
overheating
routine.
Check
for
interference with the fan or front end drive components
by foreign material, loose or broken surrounding parts .
Check for loose carburetor mounting. Check for vacuum
leaks.
Check
power
steering.
*See CTS or CGES.
CGES-215 Page 34
PRINTED IN UNITED STATES OF AMERICA
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