Ignition Service: Coil Replacement
NOTE: Flywheel removal and coil, points and condensor replacement are the same for a lot of OMC type motors through the 50s and 60s and 70s. This is the "universal type magneto" found on many models through the 50's and into the 70's including the 5.5, 6, 9.5, and 10. The shape of the flywheel will be different on many of the larger modles, however it's still simply three screwholes for fitting the harmonic balancer puller tool as outlined below.
The coils and flywheel removal procedures are the same for many of the larger motors of the same time period including the 25 up to 35 horse.
the differences would be accessing the flywheels and their shapes on the other mentioned models. Removal is the same.
A HARMONIC BALANCER PULLER, 3/4" socket wrench, screwdriver, 7/16" socket and box wrench, a 3/8" box wrench, and a
small piece of rope will all be required for this job.
Tool cost is about $40 for everything. Certainly not a bad investment
if you plan on keeping a motor or two.
NOTE: I found it easiest to remove the gas tank
before removing the
flywheel
4 - 7/16" bolts hold the gas tank in place.
It is also necessary to loosen the
gasline
a 7/16" nut.
Next, remove the 4 bolts
easily accessible with a 7/16" socket wrench and short extension.
Removing the carb primer pump 3/8" nut
seen in the center of the picture.
follow the primer pump knob and rod to the carb, look to the left of the rod and locate the primer plunger.
the plunger has the 3/8" nut on it.
On TN Models, locate the shift lever
and loosen the flathead screw
holding the lever in place and remove the lever.Lift the tank slightly
and locate the
screw which holds the shift lever rod in place.
loosen this screw.
Then
pull down on the rod, below the tank.
This allows the shift rod to come down slightly.
Next
lift up on the primer pump knob and rod.
while lifting the tank and holding the primer rod,
turn the tank slightly to your right and lift the tank up and off the motor.
This allows easy access to the flywheel.
FLYWHEEL REMOVAL FOR TD AND TN
They are slightly different, so look at pics first.
TN MODEL INFORMATION
TN-26,27,28 1950 - 1953
FLYWHEEL REMOVAL
TN MODELS ONLY!
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1946 to 1949
Johnson TD-20
service information
TD model FLYWHEELS
are removed slightly differently
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Take the rope and
For TN AND TD ( and many OMC/Johnson/Evinrude/Gale/Hiawataha/Sea King/etc 3hp up to 35 hp plus more )models, string rope into the
lower spark plug hole.
Next
Johnson TN-25,26,27,28 (or OMC universal) Flywheel removal
ON TN models, remove the 3/4" nut and washer from the flywheel.
On TN models, turn the flywheel until the rope
stops the flywheel from turning, place the socket wrench on the nut and strike the wrench with a hammer to loosen and remove
the 3/4" nut and washer on TN models OR
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Johnson TD-20 flywheel removal
ON TD-20 locate the 3/4" nut center of the flywheel.
On TD models, turn the flywheel until the rope
stops the flywheel from turning, place the socket wrench on the nut and strike the wrench with a hammer to loosen and remove
turn nut on TD-20 model flywheel until it "pops" off the crankshaft.
shown is the HD mag, essentially the same setup.
To see the coil, points, and condensor on the magplate assembly of the TD-20 click here
this page is showing the HD-25 but is essentially the same as the TD-20 motor.
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Following is for TN model ignitions.
Next
place the harmonic balancer removal tool in line with the (3) three screwholes on top of the flywheel.
I always place the recoil part
to add a bit of support to the screws
as opposed to using washers
Next
insert the 3/4" puller bolt and tighten just to the top of the crankshaft(where you removed the flywheel 3/4" nut from).
With a small claw hammer
quickly rap the top of the puller bolt.
And
the flywheel should pop off.
A couple of hits with the hammer may be required.
You can hold the bolt while rapping the top of it
and pull upward while striking the bolt.
With the flywheel off, it's easy to see that the coil on the
left is cracked and the culprit responsible for no spark.
Three flathead screws hold this particular coil in place.
There is one more smaller screw located
to the right which holds two wires onto the points.
This screw must be removed as it is attaching a wire from the coil to the points.
Lifting the coil up
shows further damage to the coil. The bottom is broken off of this coil. This can cause arcing of spark to the magneto plate, which holds the coils in place, and further damage the coil, possibly shocking you
if you run the motor with a coil in this shape.
A poorly running motor is often times caused by a cracked or otherwise damaged ignition coil.
with the new coil in place (on the left) a quick cleaning/sandpapering of the points won't hurt, if you are using the old points.
inspecting the flywheel magnet for rust (which is present on this flywheel) and removing it with sandpaper
is necessary to ensure proper spark.
Cleaning the parts before finishing up never hurts.
Finally, here you should also use a .018" feeler gague
to ensure proper point gap.
A tune up should take only about 15 miutes with the tools shown above.
Though not shown, an impact screwdrive may be used for nut and bold removal for particularly rusty bolts or on motors that have been sitting for a long time.
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