TM 5-4240-501-14P
IGNITION
Magna-Matic
Armature Air Gap
Armature air gap on engines equipped with Magna-Matic
ignition is fixed and can change only if wear occurs on
crankshaft journal and/or main bearing. Check for wear
by inserting a feeler gauge 1/2" (12.7 mm) in width at
points between the rotor and armature. Minimum feeler
gauge thickness is .004" (0.1 mm). (Keep feeler gauge
away from magnets on rotor or you will have a false
reading.) Fig. 47.
Fig. 47 - Checking Armature Gap
Magna-Matic Ignition
Remove Rotor
The rotor is held in place by means of a Woodruff key
and a clamp on later engines, and a Woodruff key and
set screw on older engines. Fig. 48. THE ROTOR
CLAMP MUST ALWAYS REMAIN ON THE ROTOR
(UNLESS THE ROTOR IS IN PLACE ON THE
CRANKSHAFT AND WITHIN THE ARMATURE) OR A
LOSS OF MAGNETISM WILL OCCUR.
Loosen the socket head screw in the rotor ecoup,
allowing the clamp to loosen. It may be necessary to use
a puller to remove the rotor from the crankshaft. On
older models, loosen the small lock screw, then the set
screw.
Fig. 48 - Rotor
Install Rotor
If rotor has a set screw, Fig. 48, Illus. 2, place the
Woodruff key in keyway on crankshaft, then slide rotor
onto crankshaft until the set screw hole in rotor and
crankshaft are aligned. Be sure the key remains in
place. Tighten the set screw securely, then tighten the
lock screw to prevent set screw from loosening. The
lock screw is self-threading and the hole does not require
tapping.
If rotor has a clamp, Fig. 48, Illus. 1, place the Woodruff
key in place in crankshaft, align keyways in rotor with
Woodruff key. If necessary, use a short length of pipe
and hammer to drive rotor onto shaft until .025"
(0.64mm) feeler gauge can be inserted between rotor
and bearing support. Split in clamp must be between
slots in rotor. Tighten clamp lock screws 60 to 70 inch
pounds (.7 - .8 kg m or 6.8 - 8.0 newton m). Fig. 49.
Fig. 49 - Install Rotor
Adjust Rotor Timing
The rotor and armature are correctly timed at the factory
and require timing only if the armature has been
removed from the engine, or if the cam gear or
crankshaft has been replaced.
If necessary to adjust, proceed as follows: With the point
gap set at .020" (0.5 mm) turn the crankshaft in normal
direction of rotation until breaker points close and just
start to open. Use a timing light or insert a piece of
tissue paper between the breaker points to determine
when points begin to open. With the three armature
mounting screws slightly loose, rotate the armature until
the arrow on armature lines up with the arrow on rotor as
shown in Fig. 50. Align with corresponding number of
engine model. On Models 9, align with 9, etc. Retighten
armature mounting screws.
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