Magneto Clean-up and Rebuild
If your magneto looks bad and has the internal coil bypassed or
some other malady not to worry! Itís not hard to take this:
And turn it into something like this:
The most important part of this rebuild is to have a TC-37F Parts
Manual. This is essential for identifying parts and locations. After
reviewing the parts manual these are the steps I took:
I first disassembled the magneto completely. The most difficult step
being the removal of the impulse coupling magneto member assembly this
is the plate under the Drive Member. To remove the drive you will
need to prevent the rotor from turning. I used a small hickory wedge
between the magneto rotor and the magneto frame. The nut has a tenon
which sits down inside the drive member, the threads are normal right
handed and the nut size is 11/16. After the nut is removed the drive
pulls off easily. Once the drive is removed the member assembly is
exposed. It appears that there are provisions for a flywheel type
puller to be used on the member but I used a small 2 jaw gear puller.
Just a little pressure on the center screw and a light tap on the end of the nut and the member
assembly will be in your hand.
View of removed drive member:
View of the underside of the drive member with replacement impulse spring:
Once the member assembly is removed the screws which attach the
mounting flange are exposed. Remove these screws and pull the
mounting flange away from the magneto frame. The magneto rotor may
or may not come with the flange. But since the rotor is magnetized
it usually stays in the frame.
Remove the rotor and disassembly is mostly complete. If further
disassembly of the member assembly is required, remember that there
are small springs under the pawls. With my eyesight these tend to
disappear quickly so be careful here.
Once the mounting flange is separated from the frame you will notice a
hole at the bottom of the frame as well as on the mounting flange.
This hole has a wick inside to provide oil from the oil cup on the
mounting flange to both front and rear bronze bushings. There are
brass reservoirs at each bushing so take care not to damage these.
View of magneto frame showing wick path at the bottom:
Once the disassembly was completed I soaked everything in lacquer
thinner and used a small brush to remove as much grease and grime as
possible. I put all of the larger steel parts except the magneto
rotor, in the de-rusto tank and left them for a day or so. The screws
I would reuse and the coil core were cleaned with a wire brush.
I took all of the aluminum parts over to the bench grinder fitted
with a fine brass wire wheel. I use brass on aluminum parts
mostly out of habit. In the RF (radio frequency) business aluminum
is widely used. A steel wire brush leaves small deposits of steel in
the aluminum. Steel does not conduct as well as aluminum at high
frequencies and that leads to higher insertion loss, so I have always
used a brass wire brush to clean aluminum. It probably wonít matter
either way for what weíre doing, just my preference.
(A little off topic.)
Once all the parts are clean, reassembly is fairly easy and straight
forward. The most difficult part was the wick. I purchased some
replacement wick from True Value Hardware but it can be found at most
any hardware store. Itís for oil lamps but works perfectly. Itís a
little tricky to get it pushed in so a little patience is in order.
I used a scribe to get it started and then a little compressed air
and it shot right in. I also left about a 1/4 hanging out of the
frame to mate up with the wick in the mounting flange. Whatís most
difficult was trying to ensure that the two wicks touch. Iím not
sure whether this is important and I canít be sure that they in fact
do touch but I tried.
I replaced the magneto coil, points, condenser, rotor, retainer,
coil cover, distributor cap and all of the gaskets. These parts I
obtained from Magneto Parts.
Some of these parts are pricey so you may want to be sitting down
when you order them. I also replaced all the small hardware nuts,
screws, washers and the like. The new oil cups I obtained from
McMaster-Carr, Page# 1916 of
Catalog #107. (The tinkerís bible)
Illustration of a typical gasket kit: (Note: some gaskets in this
pack are used and are included only for illustration.)
As you can see this is an easy thing to do. Replacement parts are
available so do not hesitate to take this on.