Section 05 ELECTRICAL
Sub-Section 03 (IGNITION TIMING)
05-03-4
NIPPONDENSO TRIGGER COIL SYSTEM
454, 494, 583, and 670 Engine Types
Ignition timing is adjusted by movement of trigger
coil. On 583 engine raising position of trigger coil
retards ignition. Lowering position of trigger ad-
vances ignition. On 454, 494 and 670 engines,
moving trigger coil to right retards ignition and
moving to left advances ignition.
Refer to CDI MAGNETO 04-05 then look for
Trig-
ger Coil Adjustment
after adjusting ignition tim-
ing.
Verifying Magneto Flywheel Timing
Mark Position
Prior to checking the timing, it may be necessary
to verify the position of the timing mark on the
magneto flywheel, for the following reasons:
1. To detect a missing or broken magneto fly-
wheel Woodruff key which would allow a
change of timing to occur, with eventual break
down of the engine.
2. To correctly locate and mark a timing mark on a
new service magneto flywheel.
3. To verify the correct location of the factory tim-
ing mark.
4. To detect a wrong magneto flywheel.
To verify the position of the timing mark on the
magneto flywheel or to scribe a timing mark, pro-
ceed as follows:
1. Clean the area around the spark plugs, and re-
move them.
2. Remove the rewind starter from the engine.
3. Install the TDC gauge in the spark plug hole,
(magneto side) and adjust as follows:
a. Position the magneto flywheel at approxi-
mately TDC.
TYPICAL
1. TDC gauge on MAG side
2. MAG side piston at TDC
b. Assemble the gauge to the adaptor and tight-
en the roller lock nut. Do not tighten the
adaptor lock nut.
c. Screw the adaptor into the spark plug hole
and tighten to prevent movement in the plug
hole.
d. Position the dial face toward the magneto.
Move the gauge down until the needle just
begins to move, then move down a further 5
or 6 mm (approximately 1/4 in). Tighten adap-
tor lock nut by hand.
4. Locate the piston TDC position as follows:
a. Slowly rotate the magneto flywheel back and
forth across TDC while observing the needle.
Note that the needle stops moving only as
the piston is changing direction.
b. Rotate the dial face so that “0” is in line with
the needle when it stops moving.
c. Again, slowly rotate the magneto flywheel
back and forth across TDC and adjust the dial
face to “0”, until the needle always stops ex-
actly at “0” before changing direction.
d. “0” now indicates exact TDC.
-
CAUTION
Each time ignition timing is adjusted by
moving trigger coil, air-gap must be adjust-
ed.
A06E24A
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