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2-20
TUNE-UP
SECTION 2-C
ENGINE TUNE UP AND TROUBLE DIAGNOSIS
CONTENTS OF SECTION 2-C
ENGINE
(42)
Paragraph
Subject
Page
2-9
Engine Tune Up
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2-20
2-10
Excessive
Valve
N
oise. .
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2-21
2-11
Hard
Starting , Improper Per-
formance, Excessive
Fuel or Oil
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Subject
Page
Consumption .
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2-22
2-12
Cooling
S
ys tem T
rouble Dia g-
noslS
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2-23
2-13
Engine Vibration or R
oughness
2-24
SERVICE BULLETIN REFERENCE
Bulletin No
.
Page No.
SUBJECT
2-9 ENGINE TUNE UP
The purpose of
an
engine tune up is to restore
power and performance that has been lost
through
wear,
corrosion, or
deterioration
of one
or more parts
or
units. In the normal operation
of an engine these
changes
take
place
gradually
at quite a number of points so that it is seldom
advisable to attempt an improvement in per-
formance by
correction
of one or two items
only. Time will be 'laved and more lasting re-
sults will be assured by
following
a definite and
thorough procedure of
analysis
and correction
of all
items
affecting power and performance.
The parts or units
which
affect power and
performance may be divided, for
analysis,
into
three groups in accordance with their function
in producing (1) Ign
ition
(2)
Compression
(3)
Carburetion.
The tune up procedure should
cover these groups in the order given. While
the items affecting ignition and compression
may be handled according to individual prefer-
ence
,
cor rect ion of items in the carburetion
group should
not
be attempted until all items in
ignition and
compre ssion
have been satisfactor-
ily corrected.
Most of the procedures
r
equired
for complete
engine tune up are covered
separ ately
in ot
her
sections of this manual; therefore, this para-
graph gives an outline only, with references to
the numbered paragraphs where detailed infor-
mation is giv
en.
The suggested procedure for
engine tune up is as follows:
1.
Inspect battery and cables (par. 10-17).
2. Test cranking motor circuit if
bat tery
is
in good condition but cranking speed is low
(par. 10-37).
3.
Inspect
generator (par . 10-26).
If
difficulty
is experienced in
keeping battery
charged, test
generator regulator
(par.
10-29).
4.
Inspect entire ignition syst em and make
indicated
corrections (par.
10-44).
Before r
e-
moval of spark plugs for
clean ing, wa
rm up
engine for steps 5 and 6 which should be
per-
formed before spark plugs
are r
einstalled.
5. Check
cylinder
head
bolts
for proper
torque (par. 2-16)
.
6. Test cylinder
compression
pressure
with
all spark plugs
removed , using
a
r
eliable pres-
sure gauge as follows
:
(a) Connect jumper wire between
primary
terminal of distributor and ground on engine to
avoid high tension sparking while cranking
engine. Turn ignition switch "ON".
(b) Insert rubber fitting of compression
gauge into a spark plug port and hold gauge
tightly in position.
(c) Push throttle wide open and crank en-
gine until
compress ion gauge
reaches
its
high-
est
r
eading,
whi
ch
sho
uld requir e
only
a few
revolutions of
engine.
(d) Repeat this test on all
cylinders,
making
sure to fully release pressure in gauge after
each test.
(e) The compression gauge hand should jump
to about 75 pounds on the first compression
stroke, with a few more strokes giving maxi-
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