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ELECTRICAL SYSTEMS
IGNITION SYSTEM
10-63
~:t---- CONTACT
SUPPORT
Figure 10-74-lncorrect Point Opening Obtained with Feeler Gauge
d. Checking and Adjusting Contact Points
with Cam Angle Meter
Cam angle meters have come into general
use for checking and adjusting contact point
opening with engine running, or with the dis-
tributor being turned under operating condi-
tions. These instruments measure the cam
angle, sometimes called dwell angle, which is
the number of degrees the distributor cam ro-
tates from the instant that the contact points
close to the instant when they open again. The
cam angle increases as the point opening is de-
creased and is reduced as the point opening is
increased.
Theoretically, a given cam angle should in-
dicate a definite contact point opening. Experi-
ments have proven, however, that the relation-
ship between cam angle and contact point
opening does not remain constant under all
conditions. Misalignment of breaker arm rub-
bing block with the distributor cam, wear of
rubbing block, slight variations in thickness of
rubbing block, cam wear, etc., will often cause
considerable variation in contact point opening
for a given cam
angle.
In some cases, contact
points adjusted to the given cam angle will
have the expected point opening, while in others
the point opening may be much less than the
minimum required for good ignition.
For the reasons given, it is not possible to
specify a cam angle setting which will insure
correct contact point opening under all condi-
tions. No cam angle setting is given in this
manual since checking and adjusting contact
point opening by means of dwell angle meas-
urement is not recommended.
If a dwell meter is used, however, carefully
follow the instructions of the instrument manu-
facturer. After checking or adjusting points
by this method always make a final check to
make certain that contact points
are
opening
within the limits of .0125" to .0175". In cases
where a chosen cam angle setting gives a point
opening below the minimum tolerance, the point
opening specification must be given preference.
10-46 REPLACEMENT OF DISTRIBUTOR
CONTACT POINTS OR
CONDENSER
When either the contact points or the con-
denser are to be replaced, these parts must be
removed and installed as an assembly as de-
scribed below, because the breaker arm spring
tension must be adjusted to specified limits
whenever the
breaker
arm spring and conden-
ser lead attaching
screw
is loosen
ed
for any
reason. Breaker arm spring tension cannot be
adjusted with contact points and condenser in-
stalled in a distributor mounted on engine.
Breaker arm spring
tension
is
v
ery import-
ant. Weak tension will cause breaker arm to
flutter and bounce at high speed resulting in
engine missing. Excessive spring tension will
cause rapid wear of breaker arm rubbing block
and cam, resulting in insufficient contact point
opening. On the 1949 model distributor, ex-
cessive spring tension can cause tilting of the
breaker base
plate.
1.
Disconnect t
erminal
connector lead "from
the terminal stud, detach condenser from
breaker plate, remove contact support lock
screw and remove contact points and conden-
ser as an assembly.
2. Disconnect condenser lead and breaker
arm spring from contact
support.
3. Inspect contact points, terminal connec-
tor lead, and condenser lead. Test condenser
(par.
10-50)
if a reliable condenser tester is
available. Discard unserviceable parts.
TERMINAL
CO N N ECTO R LEAD
BREAKER ARM
( '
CONDENSER
~
.L
CONTACT SUPPORT
.....
INSULATING BLOCK
.'
t
SPRING
LO CK
~)
~
NUT
Figure 10-75-Position of Contact Points and Other Parts for
Assembly
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