Use of Distributor Test Fixture

ELECTRICAL

mechanism should be checked. Proper

current. Check for these conditions where burned

engine performance cannot be obtained

contacts are experienced.

unless the centrifugal curve is within the

limits specified for the particular engine.

5. Contact Point Opening: Contact point opening

must be set to specification. Points set too closely may

Condenser: Four factors affect condenser

tend to burn and pit rapidly. Points with excessive

performance, and each factor must be considered in

separation tend to cause a weak spark at high speed.

making any condenser test.

The point opening of new points may be checked with a

feeler gauge. Use a feeler gauge on used points is not

"Breakdown" is a failure of the

recommended since the roughness of used points make

insulating material, a direct short between

it impossible to set the point opening accurately by this

the metallic elements of the condenser.

method. A dial indicator is recommended to check the

This prevents any condenser action.

point openings of used points. When necessary to

check and adjust point opening with a feeler gauge,

"Low insulation resistance" or leakage

proceed as follows: Rotate breaker cam until breaker

prevents the condenser from holding a

lever rubbing block is on the high point of the cam lobe

charge. A condenser with low insulation

thus giving the maximum point opening. Loosen the

resistance is said to be "weak".

All

clamp screw holding the contact support and adjust

condensers are subject to leakage, which up

point opening by 'turning the eccentric screw in the

to a certain limit is not objectionable. When

contact support. Tighten clamp screw, check with

it is considered that the ignition condenser

gauge again after tightening clamp screw. The contact

performs its function in approximately

points should be cleaned before adjusting if they have

1/12,000 of a second, it can be seen that

been in service. The cam or contact angle is the angle

leakage can be large without detrimental

in degrees of cam rotation through which the points

effects. It must be considered, however, in

remain closed.

any condenser test.

Contact Point Pressure: Contact point

"High series resistance" is excessive

pressure must fall within the limits given. Weak tension

resistance in the condenser circuit due to

will cause point chatter and ignition miss at high speed

broken strands in the condenser lead or

while excessive tension will cause undue wear of the

defective connections.

This will cause

contact points, cam and rubbing block.

burned points and ignition failure upon initial

start and at high speeds.

Use of Distributor Test Fixture

"Capacity" is built into the condenser

The distributor test fixture accurately

and is determined by the area of the

checks cam angle, spark advance and

metallic elements and the insulating and

synchronization on distributors removed

impregnating materials. For a complete

from the truck. It will also show excessive

check of the condenser, it is desirable to

distributor shaft eccentricity as indicated by

use a tester which will check for the above

variation in synchronization.

four conditions.

After a distributor has been repaired,

the calibration of the centrifugal advance

B-84