Book 3

20 endbell
And now we have reached the third and last main unit in the
motor, the endbell.
A good endbell must meet three requirements: it must provide a
stiff bearing area for the armature, it must not break down from heat,
and it must provide a good current conduction. I may be fastidious
when it comes to this, but my choice is either a white Mura or a
Champion endbell. The grey Mura is good and will stand up to most
E C.R A. racing, but for the fast commercial crowd, the white version
will give added security.
The heat is the worst problem in motor building today, as any
24-hour racer will testify. (Lars has still got scars from our last
enduro.) The usual breakdown of an unprepared endbell will be that
the material melts so that the brush holder and the spring will sink
down forever in the plastic. To avoid this, bullet proofing' was
invented by soldering the brush holders to a metal plate, and a few
other refinements. This has the advantage of distributing the heat over
a greater area for quicker heat dissipation
All endbells should be bullet proofed for maximum security. If
you're the lazy type, you can buy ready-made parts from Mini-Wheels
or Champion. However, knocking up your own bullet plates is not
difficult.
Get brass sheet of a suitable thickness, anything between .015 and
.040 in. are used. Cut out two plates that will fit exactly on the
endbell and drill holes for the spring post and the screw. See photos.
If you are using brass thicker than .015, you must also file a notch
across the plates, or the brushes will ride too high.
Next step is to file down the brush holders as per figure. Then
comes the tough part, soldering this modified brush holder to the
plate in exactly the right position. This will need patience and many
resolderings, in all likelihood. The brush holder must be exactly
centred, or you will have difficulty controlling the timing, as I pointed
out earlier. Also make sure that the brush holder will be close to the
com, for maximum brush stability. About .012 in. between the com
and the brush holder is the ideal.
The next step is the clip, which must fit tight against plate and
brush holder. If necessary, reshape to fit, then solder it in place. The
clip should be soldered to both the plate and the brush holder.
Lastly, solder the post protector over the hole for the spring post,
and clean up the job.
NOTE: use high-temp solder for the bullet plates. The endbell
assembly can actually get so hot that common solder will melt.
The endbell must be modified to accept these plates. Get an X-acto
knife for cutting down the edges around the brush holder, and afterwards
file the area flat.
21