Figure 4-15. Timing Marks

TM 10-3930-633-12

loosening the clamp bolt at the base of the

operation. Start the engine and accelerate it to

distributor and rotating the entire distributor

approximately 2000 RPM. If the ignition timing

counterclockwise to advance the timing, clock-

advances, the centrifugal advance mechanism is

wise to retard. Tighten the clamp bolt when

functioning properly. Note the engine speed when

proper timing (see table 4-4) is obtained.

the advance begins and the amount of advance.

e. Accelerate engine to 2000 RPM, in steps,

Stop the engine.

t o verify that timing advances. If advance

(2) Unplug the vacuum line and connect it to

mechanisms are not operating, report to direct or

the distributor vacuum advance unit. Start the

general support maintenance, or replace the entire

engine and accelerate it to approximately 2000

distributor.

RPM. Note the engine speed when the advance

begins and the amount of advance. Advance of

f. Disconnect timing light and tachometer, and

the ignition timing should begin sooner and

install plug in timing hole.

advance farther than when checking the cen-

trifugal advance alone. Stop the engine.

(3) If advance mechanisms do not operate

properly, replace the distributor and refer the

defective unit to direct or general support

maintenance.

b. Removal. The distributor is driven by a

helical gear on the camshaft which maintains

engine ignition and valve timing. To avoid the

necessity of retiming the engine, take care to

mark the proper position of distributor and rotor

prior to removal; and avoid disturbing crankshaft

position during the time the distributor is

removed.

(1) Refer to figure 4-16 and disconnect

vacuum tube (1) from distributor.

(2) Pull spark plug wires (2) and coil wire (4)

from distributor cap.

(3) Scribe or scratch a mark on the

distributor body and the cylinder block boss to

indicate the proper position of the body, and

remove the distributor cap and scribe another line

indicating the position of the rotor. These lines

Figure 4-15. Timing Marks

will be used when installing the distributor, to re-

4-39. Ignition Distributor

establish proper ignition timing.

(4) Remove screw (15), lockwasher (16) and

a. Test. Test of the distributor requires a

clamp (14). Lift distributor assembly (17) out of

timing light to be connected and used in the same

cylinder block.

manner as for setting ignition timing, outlined in

NOTE

the preceding paragraph. Refer to paragraph 4-38

Do not rotate the engine crankshaft while the

and perform steps a, b, c, and d, then proceed as

distributor is removed. Otherwise, the engine will

follows:

have to be retimed.

(1) Check the centrifugal advance for proper

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