Specifications

MAGNETO SERVICE INSTRUCTIONS
FAIRBANKS-MORSE TYPE FM-X4B7A
Y-97 Series
Wisconsin No. Y-97-$2 (With GD-93C-4 DRIVE GEAR) FOR MODEL VH4D
GENERAL DESCRIPTION
Fairbanks-Morse Type FM-X4B7A Magneto is designed
and engineered to provide quick easy starting and maximum
dependability of operation with minimum service. The com-
pact a~nico magnetic rotor assures an intensely hot spark
under most operating conditions,
SERVICE PROCEDURE
The first step in magneto field servicing is to examine
the magneto for corroded high tension towers, broken wires,
or high tension wires not pushed far enough into the magneto
tower to make good contact.
Then test the ignition spark while engine is being
cranked. If a strong spark is observed, the magneto is not
the cause of engine malfunction. If no spark is seen, pro-
ceed with servicing magneto.
SERVICING BREAKER POINTS, FIG. 1
Remove the end cap cover, distributor rotor and the end
cap. Then inspect the breaker points for pitting, oxidation
and shorting. If points are worn or shorted, they should be
replaced.
To remove the poiut set, take out the breaker arm ter-
minal screw releasing the breaker arm spring, coil lead and
condenser lead. Remove the fulcrum pin snap ring and slide
the breaker arm off the fulcrum pin. Remove the contact
support locking screws and lift off the contact support.
The installation of new points is the reverse of the re-
moval. After the points have been installed, they should be
adjusted to the correct clearance of 0.015 inch at high point
of cam. Be sure the points are clean and bright before
adjusting them. Insert a screwdriver in the slot of the sup-
port bracket and pivot it between the two small bosses on
the bearing support until the desired clearance is obtained
Then clean the points again before sealing the magneto.
COIL
CONDENSER
MEASURE BREAKER
POINT GAP WHEN
OPEN. ADJUST TO
.015 INCH
BREAKER ARM
LOCKING SCREWS
CONTACT PLATE
ADJUSTING SLOT
Fig.
1, BREAKER POINT ADJUSTMENT
FIELD SERVICE NOT RECOMMENDED
The cam wick, if dry or hard, should be replaced with a
new factory impregnated wick. Other than this the magneto
does not require field lubrication. No attempt should be
made to oil or grease the magneto bearings. The magneto
lubricant should be replaced only during the overhaul of the
magneto by a Fairbanks-Morse authorized service station
using recommended lubricant and factory engineered parts.
Coil and condenser replacement while simple are not
re©ommended unless adequate test equipment is available.
N0 $*ttempt should be made to remove magnetic rotor from
housing unless specific instructions for releasing the shaft
are available.
INTERNAL TIMING, FIG. 2
If, for any reason, the magneto ha-~ be~’n dismantled to
the extent that the distributor gear has been removed the
teeth must be properly meshed with those of the magnetic
rotor gear upon reassembly. The gear teeth are marked to
facilitate internal timing. The single marked tooth of the
rotor gear must mesh between the two teeth ,of the distributor
gear designated by the letter C.
Marked Tooth of
Rotor Gear Must
Mesh Between
The ’C’ Mark of
Distributor Gear
Fig. 2, INTERNAL TIMING GEARS
TIMING THE MAGNETO TO THE ENGINE
If the magneto has been removed from the engine for
servicing, the operator must follow the engine manufacturer’s
instructions for timing the magneto to the engine. Refer to
’Magneto Timing’ in engine instruction manual. When
installing the magneto on the engine, be sure the magneto
is properly attached and that the housing to engine gasket
is in good condition.
SPECIAL DRIVE GEAR, FIG. 3
The magneto is equipped with a special drive gear
mounted directly on the impulse coupling. If it is necessary
to replace the drive gear, special care must be exercised in
reassembly. It is possible to be off lgO
°
in timing if gear is
improperly mounted.
Assemble gear as follows: Remove magneto end cap
cover and turn distributor rotor until it is in firing position
for No. 1 cylinder. Retain rotor in this position and fit the
drive gear to the impulse coupling lugs so that the prick
punch mark on front of gear is located as shown.
DRIVE
GEAR
PLACE DISTRIBUTOR
ROTOR IN FIRING
POSITIOCq
No. I CYLINDER
- THEN -
~_..~MOUN T GEAR
i
WITH ’PRICK
PUNCH’ MARKED
GEAR TOOTH
LOCATED THUS
Fig~
3, DRIVE GEAR MARKING AND ASSEMBLY
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