SmokStak

By Staff
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Schematic for magneto/battery hookup as shown in an old United manual.
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Schematic for magneto hookup only.

The following comes from a recent topic on SmokStak, an Internet
engine bulletin board (go to http/www.engineads.com/ smokstak.cgi).
As ever, various individuals started, commented on and concluded
the following bulletin board thread.

I have a really nice, barn-fresh Associated with loads of
character gained through the years. It runs great, but it’s a
real bear to start. I would like to start it with a battery and
coil and then switch it over to the mag. My question is, should I
install a two-way switch to switch between the mag and ignitor or
should I install a two-pole, two-way switch so I can ground the
magneto when the battery is in use? Will I need a resistor in the
grounding circuit so the mag is not shorted directly to ground, and
what size and value of resistor might I need? -Al

A single-pole, double-throw switch will be just fine. There is
no need to ground a low-tension mag while the engine is running.
The AC voltage generated by the mag when not loaded will be quite
low compared to the spike created when the igniter trips. Bearing
condition is critical in low-tension mags, as is strength of the
magnets, and it must be correctly timed to the engine. I would
guess you have a problem in one of these areas. – Ken

Thanks Ken. This engine is in ‘as found’ condition and I
have done nothing to it. The mag timing is good, but the magnet
could be weak. The armature bushings are a bit worn, but not so
much as to allow dragging on the fields. This thing is completely
original and I want to leave it for the next generation to restore.
I am not even going to clean it. I had it mostly apart and repaired
the rod bearing and the wrist pin. It is a lot of fun to run and
people point and laugh at it. I just love it. – Al

Yes, some of the nicest running engines I have seen were in
‘as found’ condition. Nothing wrong with that, it shows how
these old engines spent most of their working life. It’s
getting hard to find engines and the old, larger tractors in that
condition. -Ken

I just installed a rebuilt gear-driven mag on my small
Associated. I measured the voltage from it while the engine was
running off the battery and coil and got about 5 volts. This
sounded low. The engine will run off the mag if the rpms are kept
up and will start a crank if you turn it fast. Does this sound
normal? – Mike

Al, here is the diagram out of a United manual (see next page)
for mag/battery hookup. Notice how the low-tension spark coil is in
line with the ground. – Keith

Keith, looking at the diagram you posted, is the coil wired
correctly? I would think the coil would be between the battery and
the igniter, not between the battery and ground. Does it make a
difference? I have not gotten to the point where I have worked on
this type of battery and low-tension coil ignition and am just
wondering. – Jim

I think the coil is actually between the battery and the
igniter. They have the positive side of the battery going through
the coil and to the ground on the igniter. The negative side on the
battery goes to the stationary point on the igniter. It isn’t
the way we are all used to hooking up coils, but I have my Stickney
wired this way because it showed it the same way in the owner’s
manual. It runs great. – Bryan

Positive and negative make no difference with a low-tension coil
and igniter. It is wired this way, in this case, to isolate the
coil from the magneto. – Ted

If your mag is working correctly it does not have to be spun to
start. Just like any other hit-and-miss engine it should snap right
off with a pull of the flywheels. – Mike

Mike, no disrespect, but what are you talking about? As I
understand this thread, the low-tension mag being discussed does
not have an impulse. It’s impossible to generate electricity
without it being spun at a relatively high rpm (60-100 engine rpm).
That’s with a good mag with good magnets. That is why there are
impulses on high-tension mags, to replace the huffin’ and
puffin’ required to generate enough speed by people power. The
point I am trying to make is that an igniter engine can be started
on a mag, but it is more than a casual ‘flip’ of the
flywheels. – Mark

Harry has very good instructions on the Associated
magneto/ignitor in the ‘ignition’ section of his web site
at: www.oldengine.com/maglma.htm

Pay particular attention to the information regarding the push
pins on the magneto and the relationship they have with the trip of
the igniter. When the magneto revolves there are two peak times of
output. If the igniter is timed to trip at the moment the magneto
is at peak you will get a viable spark. It does not require lots of
cranking and/or high revs to work. There is also info on a simple
method of checking the magneto to see if it is working. Al, check
it out before you go to all the trouble of setting up the
battery/coil rig. I just finished fixing one that was just like
yours, and now it starts off the mag with one easy flip of the
flywheels. The timing of the magneto with the push pins and trip
finger is critical. – G.V.

I hope I didn’t open up Pandora’s box. Mike said a mag
did not have to be spinning to create a spark. That is true in an
oscillating mag. But the spring does the same thing as spinning a
mag when it trips. A small engine without a large amount of
flywheel inertia is very easy to spin to sufficient speed to start
with a simple flip of the flywheels. 1 agree and completely
understand what you guys are saying. 1 was talking about getting
that same speed with flywheels of 2,000 to 3,000 pounds. It
can’t be done without some huffing and puffing.

A battery start can be started with only a rollover on
compression (or even a flip of the igniter while at rest on
compression stroke past top-dead-center). A mag that creates spark
while at rest (not spinning or being oscillated) is something new
to me, and that is what I was asking about. Low-tension mags are
nothing more than a low voltage generator. I was trying to
understand how it could generate electricity without being in
motion. Can a mag store energy while being at rest, then create a
spark some time later? Sorry for the confusion. – Mark

Mark, I re-read my post and you must have misunderstood my
description. The mag on my engine is the two-bolt type, same as a
John Deere engine. It is nothing more than a generator. It is
mounted 90 degrees to the timing gear. By disconnecting the wire
lead to the igniter and running the engine on a battery and coil, I
can measure the generated voltage between the mag wire and ground.
Peak is about 5 volts at approximately 250 rpm. I timed it using
the instructions provided in the owner’s manual; push in on the
detent button until it falls into the depression and set the engine
at the igniter trip position. With the mag off and turning it by
hand, you can feel a strong magnetic pull as it passes through the
field. I was wondering if the mag is putting out the nominal amount
of voltage, given that it will not run at slower speeds and is
difficult to start without spinning the wheels rather fast with a
crank. Thanks for any opinions. – Mike

Mark, I agree with you. As you know, Associated engines are my
favorite and I have three four-bolt mags, so I am very familiar
with starting on the mag. I can start my Hired Man by flipping the
wheels, but the mag is freshly rebuilt and it’s very strong.
Plus, the engine runs very well, so after a couple of tries it will
start by pulling back on the wheels. But it is much easier to just
use the hand crank and get the wheels spinning, and away she goes!
– Keith

SmokStak is an engine conversation bulletin board with over
50,000 messages on file and is part of the Old Engine series of Web
sites that started in 1995 as ‘Harry’s Old Engine.’
Harry Matthews is a retired electronic engineer and gas engine
collector from Oswego, N.Y., now residing in Sarasota, Fla.

‘Positive and negative make no difference with a low-tension
coil and igniter. It is wired this way, in this case, to isolate
the coil from the magneto.’

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