Energy Transfer Magneto
- Hoyt McKagen
Energy Transfer Magneto is easily made from standard alternator as
used on most earlier model Hondas of all sizes. Alternator is a six pole,
split coil arrangement with a perma-magnet button rotor. There are
differences in the design among models and year, but all are suitable
for
conversi
on.
Many of
these
will
swap
between
motors,
but since
individu
al units
are
wound
respectiv
e to
demands
of the
number
of spark
coils, the
number
of
cylinders
/coils
should
be the
same.
ETM is
wired so each coil primary has a stator coil, set of points and capacitor.
Each of these components has two connections, one of them usually
grounded as mounted. To complete ETM wiring, any remaining ground
connections are made, and components are connected together at the
other ends, that best being done by one primary lead from each stator
coil pathed thru points, cap and coil in their usual mounted positions.
The primary may have sockets spliced into it at various places to
facilitate
connections.
This same lead
can be
extended to the
kill switch; for
twins and
multis that can
operate by
connecting the
involved stator
coils together. Usually spark coils, points and caps can all be stock
components as used with the original cycle, and mix and match is often
successful. I've got a CB360 barking with Yam coils from a CDI model
Triple coils and in general, CDI coils often give slightly better results.
Alternator coils are in two sets distinguished by wire size and number
of turns. As shown, there are four lighting and two iggie coils. On the
stator, the iggie coils are opposite each other and so are pairs of
lighting coils. The two lighter-gauge iggie coils are wired in series and
are connected to brown or pink common lead, along with one end of
the lighting set. On single-coil setups (thumpers and 360 twins), the
iggie coils can be used as wired, with the brown lead grounded and the
yellow lead from iggie coils used for the primary lead. On twin-coil
setups (180 twins and multis) the iggie coils must be separated at one
end from common and an extra primary lead brought out from the
disconnected end. Somewhere between these two coils their connection
must be isolated, spliced to a wire and lug, and grounded to a stator
mounting bolt.
Battery/coil systems flow current thru coil when points are closed,
building magnetic field around primary to saturation. When points
open, current stops flowing and magnetic field collapses. Energy
contained in field excites voltage flow in both coils, generating spark
voltage in secondary. Primary coil and capacitor form a resonant circuit
that also feeds energy into secondary coil, prolonging spark and
probably accounting for spark 'ringing'. Battery/coil system thus has
two instantaneous sources powering the spark.
ET magneto operates in essentially the same way except for the stator
coil subbing for the battery, hence the similarity in the wiring.
However, the magneto has an extra instantaneous source: there is
energy stored in the magnetic field at the rotor/stator interface that is
also available to the spark as the points open. A battery cannot supply
that kind of pulse! But stator coil also can't give continuous power, so
points must open and spark be produced when it's giving its best.
Usually, the magnetic pulse isn't wide enough to give you the full
original range of advance, so it may be limited to about ten degrees or
so (by brazing blobs onto the advancer stops) or advance simply be
done away with. I do the latter and find it has no effect on performance
nor if well tuned are they tougher to fire up.
Usually the desired pulse isn't where keyway places the stator. Often
when setting these up a specific procedure is helpful: Wire and connect
the ET setup and lock out or limit the advance mechanism. For timing
purposes, temporarily lock in full advance. It's helpful to loosen the
valve adjuster screws, to keep spring pressure from moving the motor;
indeed one can also set these so the motor will stay in the desired place.
Remove the rotor and replace it on key, loosely secured. Time the
points to the appropriate full advance mark(s) on the rotor ... get it dead
on using a meter or continuity checker to verify opening point. Take
the rotor back off and remove key. Place rotor at the point of optimum
pulse and secure it moderately hard, for testing spark. The key is not
needed to make this a secure joint.
Optimum pulse we would expect to be at the point where the rotor and
stator poles have overlapped perfectly, where magnetic interaction is
strongest. However, a real magneto as found on tractor and Harley
usually has the points open at some point previous to that. The practical
reason is, we don't want the spark to be fired as the field strength is
instantaneously beginning to decline. We want a robust increase in
magnetic field interaction to be going on at the rotor/stator as points
open, because that means energy will continue to be fed to the spark
and even at increasing rate. In fact, the spark continues over about the
same angular distance that one pole initially lags the other. So I advise
the optimum point be with about 80% pole engagement and
correspondingly more if you run some auto-advance.
Make sure points are clean, as magneto performance depends on
passing the heaviest possible current thru them. If points are clean and
it's wired right it should make spark while turning it over with a
wrench. Some degree of tuning is available by putting rotor in different
relative positions on crank. After spark intensity is thus optimized,
torque rotor down and carefully transfer the timing from the points
opening position(s) back to the rotor for your reference marks for next
time you work on iggie.