With the advent of the spark plug and battery operated "buzz coils",
high tension magnetos came into being to eliminate batteries and feed
the higher voltage needed to overcome the open spark plug's high resistance gap.
Tension is simply another word for voltage or potential. (Electro Motive Force
for us engineers.) Low tension is on the order of 1000 volts or less and high tension
implies 1000 volts or more. There's a wide range here, but the high tension of an antique
magneto is not as high as a modern electronic ignition. The main point is that high
tension implies a spark plug engine and low tension implies an igniter engine.
High tension magnetos also use capacitors (condensers) across their "external points" because
sparking is now undesirable as it causes unnecessary wear and tear on the point
surfaces. A high tension magneto uses a "secondary" "step-up" winding to
create the higher voltage, much the same as in a step-up transformer.
The WICO "EK" is one popular example of a HIGH TENSION spark plug Magneto.
From the WICO MAGNETO Type EK Instruction Book
The Type ONE Drive (Witte Engines)
In the Type ONE drive, the magneto is operated by an eccentric and strap from the crank shaft or cam shaft of the engine. There are several forms of this drive, but they are all the same in principle. The armature is held against the cores by the return spring and by the magnetic attraction of the cores. The spark is produced by pulling the armature about 1/16" to 3/32" away from the cores. (This is called tripping the armature.) This is done by the drive spring which bears against the end of the rocker arm and is compressed as the eccentric turns until finally the trip shoulder inside the spring bottoms against the end of the rocker arm and instantly breaks the magnetic contact between the cores and the armature which is then snapped away from the cores by the compressed drive spring. As the eccentric continues to revolve, the pressure of the drive spring is relieved and the return spring draws the armature back to the cores again where it remains until the proper time for again making the spark.
Timing Control: The time of the spark is controlled by the advance lever which adjusts the rocker arm back and forth with relation to the trip shoulder. The advance lever can always be set in two positions (advance and retard) and on some engines, it can be set in a third (cut out) position, which will prevent the armature from tripping and thus no spark will be produced. The advance lever should be in the retard position for starting and in the advance position for running.
Type TWO Drive (JAEGER, ECONOMY Engines)
This drive is designed for operating the magneto from the valve push rod of the engine by means of the trip finger. The armature is held against the cores by the return spring and by the magnetic attraction of the cores. The spark is produced by pulling the armature about 3/32" away from the cores. (This is called tripping the armature.) As soon as this is done the armature is released ("latched off") and the return spring quickly lifts it back to the cores. The movement of the armature is accomplished so rapidly that it is on the cores about 95% of the time.
The armature is tripped (pulled down) by the rocker arm when it is engaged by the trip finger on the push rod. After the armature has moved down 1/8", thus opening the breaker points, the "latch-off" screw disengages the rocker arm from the trip finger latch and the return spring replaces the armature upon the cores. The trip finger latch bears against a spring, and when the latch engages the rocker arm this spring is compressed until the end of the latch-rod bottoms against the advance lever, and by so doing trips the armature. Then the compressed spring drives the latch forward and thereby gives a very rapid movement to the armature.
Timing Adjustment: When the magneto is installed on the engine, the proper timing is secured by locating the bracket, which supports the trip finger, at such a position on the push rod that the magneto trips at the end of the compression stroke (TDC) when the advance lever is in the starting position. Engine users should not tamper with the setting of this bracket unless it is found that something has occurred to make the magneto trip otherwise than above.
Type THREE Drive
The type 3 drive is a combination drive, possessing some of the features of each of the first two. This drive is operated from the push rod as in the #2 drive, except that there is no "latch-off" of the trip mechanism, and the drive spring, return spring, rocker arm and trip shoulder operate in exactly the same manner as in the #1 drive. The lock nut is provided for locking the trip rod in position when timing the magneto as in the #1 drive.
The spark advance is obtained by means of an advance lever attached to the rocker arm. To advance the spark, the advance lever is pushed down into position between the rocker arm and the trip washer, thus the trip shoulder bottoms against the rocker arm earlier in the rotation of the cam.
The proper dimensions of the rocker arm and ignition rise on the cam will be determined by design for each particular type of engine.
Care of TYPE EK WICO Magnetos
The following simple instructions for the care of the Type EK magneto tell all that you need to know to help keep it in perfect condition. Follow these instructions exactly and do not experiment.
The need for making adjustments or replacements will seldom, if ever, arise, but all parts of the magneto are so accessible that adjustments and replacements can easily be made when required.
MAGNETS: Do NOT remove the magnets! You will instantly destroy their magnetism and gain nothing, because every part of the magneto that may conceivably require renewal can be replaced without removing the magnets and without weakening them.
MOVING PARTS: All moving parts can be withdrawn from the magneto by lifting the armature from its magnetic contact with the cores. This operation does not weaken the magnets. When replacing the armature make sure that the oil pad slips over the guide rod.
REMOVAL OF COVERS: The covers of the magneto are held in place by the band which is fastened by four screws, two at each end of the magneto. The removal of these screws allows the band to be lifted and the covers to be removed.
OILING: The type EK magneto will last for years if properly oiled, but if allowed to run dry, its life will be very much shortened. The drive mechanism should be oiled each day the engine is used. Oil the magneto at the marked oil hole once a week with regular engine oil.
BREAKER POINTS
The breaker point contacts are perfectly adjusted at the works of the Wico Electric Company, and no re-adjustment will be required through thousands of hours of use, except when installing new contacts, at which time proceed as follows:
On engines using the Type #1 eccentric and strap drive, the breaker point contacts should just open when the armature is about 1/16" away from the cores. On engines using the Type #2 push rod drive or the Type #3 combination drive the breaker points should just open when the armature is 3/32" away from the cores.
REPLACEMENTS
SPARK WIRE: The spark wire on the latest type of magneto is provided with a spring clip soldered to the end of the wire which snaps into the terminal block. To replace the spark wire it is only necessary to pull the old wire out of the terminal block and push in a new one. In some of the earlier magnetos the wire is provided with a threaded sleeve on the inner end, which screws into a shouldered brass washer in the terminal block. To replace this spark wire, it is necessary to unscrew it.
TROUBLE SHOOTING
If ignition trouble is suspected disconnect the spark wire from the plug and observe spark between wire and engine frame, by holding end of wire about 1/8" from the frame while cranking engine.
If no spark is produced when the magneto is operated, the trouble can be located by proceeding as follows:
See that the armature returns and makes a firm contact with the cores after being tripped off. Failure to make firm contact indicates a weakened or broken return spring or friction in the moving parts because of lack of oil. Remove any dirt between the armature and the face of the cores.
Turn the flywheel over slowly and see that when the armature is tripped it snaps quickly away from the cores. Failure to do this indicates binding or friction or a broken drive spring.
Remove the front cover and remove any dirt from the surfaces of the points. See that electrical connections are tight at both the point connector nut and the ground screw. CHECK THE CONDENSOR!
The distance between the spark plug points should be from .015 to .025 inches. The insulator inside the base of the spark plug must be kept clean because the electricity from the magneto can leak through the carbon on the insulator instead of jumping across the points, making it hard or impossible to start the engine or making it fire irregularly.
A plug will sometimes show a spark when tested outside of the cylinder and yet fail to fire the engine when replaced in the cylinder. This shows that the plug is "leaky", because of carbon or because the porcelain insulator is cracked. A "leaky" plug will spark outside the cylinder and not inside because the spark can jump through the air easier than it can jump through the compressed charge inside the cylinder, especially when the engine is cold. Trouble is sometimes caused (especially in two cycle engines) by spark plugs that do not extend far enough into the cylinder and thus a pocket is left at the end of the plug in which dead (burnt) gas collects. Such gas can not be fired by any spark. Spark plugs so located tend to carbonize quickly because they operate at too low a temperature.
Fairbanks Morse "Z" High Tension Magnetos
All "Z" Engines are equipped with a high tension rotary magneto of FM's own make, with the exception of course of the
2 H. P. battery equipped hit and miss engine. The Fairbanks-Morse Type "R" Rotary High Tension Magneto, as it is called,
produces a hot, fat spark that makes starting easy. The magneto on the 3 H. P. and larger sizes has an impulse coupling.
With the Type "R" magneto timing is definite. The engine is not subject to timing variations occasioned by the wear of operating mechanisms such as are encountered with magnetos of the trip or oscillating types. Accurate timing means maximum power
and greater fuel economy. This magneto comes to you sealed and mounted on the engine. It is as near trouble-proof as possible.
It is dust, dirt and water-proof. There are no places to oil so that over-lubrication or lack of lubrication is definitely forstalled. The
roller bearings are packed with a special grease and require no attention whatever on the part of the operator. Each magneto is
carefully tested for "quick starting" and fully guaranteed.
