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In our last issue, I
talked about one part of the Model "T" ignition system.
Various timers were discussed and I recommended the Anderson Timer that is
now being manufactured by Bob Thompson. There are two other things
which are vital to the smooth operation of the original system the
"T" used. They are the magneto and the coils.
There's a lot of discussion about whether the original coil/timer system
can work as well as an after-market distributor. Having run both
systems in my 12 and 22 T's, I can tell you that my personal feeling is
the original coil/timer system can work just as reliably and with no more
adjustment than a distributor system IF
the coils have a good condenser, are adjusted correctly and
the magneto puts out enough voltage OR
you use a 12 volt battery! We'll talk about the 12 volt option
further down the page.
Let's talk briefly about the magneto. To have a sweet running
coil system you must have a magneto that will put out about 7 volts while
idling and about 25 volts or more when driving down the road. A
number of factors can effect the magneto's output. The most common
problem is probably magnets which over a period of 75 years have lost much
of their magnetism due to heat and vibration. While it is certainly
better to recharge low magnets while out of the engine, I have recharged
them successfully using three 12 volt batteries in series and carefully
lining up the magnets using a compass. The method is described in a
number of publications so I won't go into details here.
Another cause of low voltage from the magneto is wear on the engine's main
bearings! As the bearings wear the space between the magnets and the
coils increases and the voltage drops rapidly! During the Model
"T" era, a number of companies offered gadgets designed to
control the end-play to keep the magnets near the magneto coils but I know
of none that are available today. About the only solution I know of
is to rebuild the engine and set the clearance correctly when you
reassemble.
The last set of problems we can run across with the magneto are no voltage
at all! This will generally be caused by a shorted or open magneto
coil. The magneto coils have to withstand a very hostile
environment. They are constantly bombarded with very hot oil which has
minute particle of metal in it! If some of these particles work
their way through the insulation a short may result. Sometimes it is
possible to burn a short off by using the same setup we use to recharge
the magnets. A heavy jolt of high amperage current for 10 to 15
seconds may burn
off the shorting material. This method is not for the "faint of
heart" though.
An open magneto coil system is also a possibility. Unfortunately,
this usually can not be repaired without disassembling the engine.
And one last place to check when you have no or low voltage is the magneto
contact terminal on the top of the hogshead. Sometimes fluff from
the bands will build up here and work its way between the solder point on
the coil assembly and the contact point of the terminal. It's easy
to check and should be the first thing you look at if you have a low
output problem. Just take out the contact terminal and look for
fluffy material on the solder point and contact point. Clean them
and cross your fingers.
You can check the voltage with an inexpensive AC voltmeter. Yep!
the magneto is alternating current not
direct current like the battery. And by the way... The
alternating current means that the spark lever should be set slightly
differently for magneto running than for battery running. By careful
experimentation, you'll notice a definite "sweet spot" for the
spark lever that the magneto and coils really like. Look for it!
It's well worth finding.
If your magneto just won't "cut the mustard", don't give up!
A 12 volt battery will make the old "T" run just about as well
as the magneto and will actually run a little better
at slow speeds because the magneto drops to 6 or 7 volts when crawling
along in the parades.
See you down the road…
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