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2-24
TROUBLE DIAGNOSIS
ENGINE
(46)
13 pound cap and the tube and fin radiator, the
temperature may reach 190°-195°F. These con-
ditions must not be mistaken for overheating.
In cases of actual overheating the following
conditions should be checked:
1. Excessive water loss. See subparagraph b
above.
2. Slipping or broken fan belt (par. 2-27).
3. Radiator air passages clogged with dirt,
bugs, etc.
4. Radiator thermostat stuck in closed posi-
tion
(par.
2-28).
5. Restriction in radiator, hoses, or water
j
acket
passages.
6. Improper ignition timing (par.
10-47).
7. Improper carburetor adjustment (par. 3-
12).
8. Exhaust manifold valve stuck (par. 3-11).
9. Shortage of engine oil or improper lubrica-
tion due to internal conditions.
10. Dragging brakes (par. 8-15).
2-
13 ENGINE VI
BRATION
OR
ROUGHN ESS
If
unusual vibration or roughness develops
in the operation of a car, test first to determine
whether the condition originates in the engine
or in other operating units. Time will often be
saved by checking the recent history of the car
to find out whether the roughness developed
gradually or became noticeable following an
accident or installation of repair parts.
Vibration is usually most pronounced when
driving at a certain speed. If the engine is run
at the equivalent or critical speed with car
standing and transmission in neutral, the vi-
bration will still exist if the engine, clutch, or
transmission is at fault. By running engine at
the
critical
speed with the transmission in high
gea r and
clutch
disengaged, any vibration orig-
inating
in the
transmission
will be
eliminated.
If
the vibration does not exist
during
the
tests with car standing still, refer to
Diagnosis
of Rear Axle Noises (par. 5-3,
5-4,
5-5) and to
Car Roughness or Vibration (par. 6-12).
If
tests indicate that the vibration originates
in
the engine or clutch, the following items
should
be investigated and corrected as re-
quired.
a. Bent
Fan Blade s
Fan blades
may be bent by accident or by the
objectionable practice of t
urning
the
engine
by
means of the blades. Vibration caused by bent
blades may be determined by running the en-
gine at the critical speed with the fan belt
temporarily removed.
b. Eng ine Tune Up
An engine which is not properly tuned up
will run rough and vibrate, particularly at
idling and low speeds. A thorough engine tune-
up operation is the proper correction (par.
2-9) .
c. Eng ine Mountings
Vibration may be caused by broken or de-
teriorated engine mountings, or by mountings
that are loose or improperly adjusted. Adjust
and tighten loose mountings (par. 2-31) or re-
place faulty mountings.
d
. Crankshaft Balancer
Loose or broken springs in the crankshaft
balancer will cause a pronounced rattle which
usually becomes noticeable before the condition
is such as to cause vibration in the engine. If
the balancer is damaged by accident in such
manner that the parts cannot function freely,
extreme roughness will be produced which may
eventually cause breakage of the crankshaft if
it is not corrected. A balancer which shows ex-
ternal evidence of damage or which is sus-
pected of being inoperative should be replaced
and the result checked, since it is not possible
to test the balancer in any other way.
e. Unbalanced Connecting Rods or Pistons
Vibration will result if connecting rods or
pistons are installed which are not of equal
weight with all other rods or pistons in
engine.
If
new parts have recently been installed, these
should be checked to determine whether they
are standard Buick parts or have been altered
in
weight by filing, machining, or other repairs.
f.
Unbalanced
Clut ch
Assem bly
or Flywheel
Engine roughness may be caused by an un-
balanced combination of clutch, flywheel, and
crankshaft even though these units are bal-
anced individually during manufacture. This
may occur if clutch or flywheel is removed
-
without marking them so that they are rein-
stalled in original position, or if new parts are
installed. An unbalanced condition of clutch,
flywheel and crankshaft may be corrected as
described in paragraph 2-34.
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