TOPIC 8. DISTRIBUTOR

TM 10-3930-644-14&P

TOPIC 8. DISTRIBUTOR

A. DESCRIPTION

C. INSPECTION

The distributor delivers the. high voltage surge, induced

The distributor cap should be removed at regular

in the ignition coil secondary, to the spark plugs at the

intervals to examine the contact points, rotor and the

proper time for sequential cylinder firing. The distributor

cap.

is mounted on the cylinder head, and is driven off the oil

pump shaft at one-half of the engine crankshaft speed.

NOTE

Dust cover under distributor cap

The distributor consists of a cast housing into which a

must be removed before points can

shaft and weight base are fitted in a bronze bushing.

be checked.

Centrifugal advance weights are pivoted on studs in the

weight base and are free to move against the calibrated

1. Check all high tension wiring for defective

weight springs which connect them to the breaker cam

insulation and poor connections at distributor

assembly.

cap and spark plug connectors.

2. Wipe distributor cap and check cap and rotor for

During the time the contact points remain closed, current

cracks or carbon tracks indicating leakage of

flows from the battery, through the ignition coil primary

high voltage current across surface.

windings, the contact points and back to the battery

3. Check centrifugal advance mechanism by

through a ground return.

Energy in the form of

turning breaker cam in direction of rotation and

magnetism is stored in the ignition coil.

As the

then releasing it. Advance springs should return

distributor breaker cam continues to rotate, the next cam

cam to its original position without sticking.

lobe is brought around to where it strikes the breaker

4. Remove dust cover and inspect contact points.

lever rubbing block and opens the contact points.

If points are badly burned or pitted, they must be

replaced and adjusted.

Replace every 500

The open contact points break the electrical circuit and

hours.

although current tends to continue to flow through the

coil because of self-induction, it is shunted through a

NOTE

capacitor to prevent arcing across the open points. The

Refer to ENGINE MAINTENANCE

stored magnetic energy in the coil collapses producing a

MANUAL, TIMING Section for proper

very high voltage in both windings. The energy in the

procedures.

coil begins to drain through the secondary high tension

lead, into the center of the distributor cap, through the

5. Replace contact

points,

dust

cover

and

rotor and then jumps to the electrode opposite which the

distributor cap.

rotor has been positioned, out through another high

tension lead and finally fires the proper spark plug.

3. INSTALLATION

The spark is sustained through several degrees of

1. Remove distributor cap and insert distributor

crankshaft rotation. At the same time, the shunted

assembly into opening in cylinder head.

energy in the condenser discharges back through the

2. Using rotor, turn distributor shaft until offset

primary circuit, but not until the spark is completed at the

tongue of distributor coupling enters groove in

plug, and the whole firing cycle starts again.

top of oil pump drive gear.

3. Install distributor clamp arm, washer and

B. REMOVAL

capscrew and tighten securely.

Replace

distributor cap and secure.

1. Remove the high tension wiring from the spark

4. Install high tension wiring to spark plugs, and

plugs and the high tension wire from coil to

connect high tension wire from distributor cap to

distributor at the coil. Remove the primary lead

ignition coil. Replace primary lead from

that runs from side of distributor to coil primary

distributor to coil, at coil primary connection.

connection. Tag spark plug wires.

2. Remove capscrew, lockwasher, and distributor

NOTE

clamp arm and lift distributor assembly from

Refer to REPAIR MANUAL for

cylinder head opening.

DISASSEMBLY,

REPAIR

AND

3. Unlock distributor cap retaining screws

REASSEMBLY and refer to ENGINE

MAINTENANCE MANUAL for proper

TIMING procedure

2-32