Tips on Repairing a Webster Magneto


| July/August 1989



Richard Hamp submitted this from Webster magneto service material with permission.  

Wherever possible, the customer should always be cautioned to have both the magneto and igniter plug repaired, because very often the magneto is blamed for trouble that is in the igniter plug.

Inspecting and Repairing the Magneto Equipment
When a magneto and igniter plug is received for repair, check carefully all parts and replace those showing any wear. Particular attention should be given to the following:

a. Bearings in end plates: Are they worn allowing the inductor to rub on pole pieces?
b. Inductor springs: Are they weak?
c. Push Finger: Has it become worn to such an extent that it will allow the push rod to slip off before the inductor has the proper oscillation?
d. Terminal screws: Do they strike the top cover? If so, it will cause a short.
e. Movable electrode: Is it working freely? Will it continue to work freely when the igniter plug becomes hot?
f. Electrode arm spring: Has this spring tension enough to bring the points together?
g. Insulation around stationary electrode: Is it burnt or have carbon deposits formed and worked in between the mica washers? In either case this will cause a short. By using a 110 volt test lamp it is easy to determine whether or not there is a short. Whenever there is the least doubt as to whether or not the insulation will stand up for any length of time, always replace it.
h. Spark points: Are they worn so badly that they will not make proper contact?
j. Terminal: Does this strike any part of the ignitor plug? If so it will cause a short.
k. Adjusting screw: Is this properly adjusted so that it opens the igniter points by striking the tail of the push finger when the magneto is tripped? This screw should be adjusted so that it just barely touches the tail of the push finger when the inductor springs are in a horizontal or 'at rest' position. This of course refers only to AM, AMM, AK, AL, AJZ, AJY and APY types of magnetos.

Testing Magneto for Voltage
After checking up on the points referred to above, remove the magneto from the igniter plug. Next remove the inductor springs and spring arm and drive the magneto at 500 RPM checking the voltage on an A.C. voltmeter. Then compare the voltage output of that particular type of magneto with that given on the voltage chart (blueprint) which we furnish to all service stations. Should the magneto not develop at least the minimum voltage shown on this chart, remagnetize and again check the voltmeter. If, after remagnetizing, the magneto gives voltage somewhat lower than the specified minimum, it may need either new coils or a new magnet.

a. Substitute a new magnet and test for voltage. If it still remains low, the trouble must be in the coils, and the original magnet should be replaced.
b. Remove the coils and replace with a new pair, first warming them in an oven to make them pliable. NOTE: Before removing the old coils, observe carefully the relation of the lead wires, and install the new coils the same way. Otherwise the two coils may oppose each other and no current result. If, after remagnetizing, the voltmeter shows no indication at all, observe the following:

Remove top cover, and examine the wires which are fastened to the terminal block, making sure they are securely fastened. Also see the opposite end of the coil is securely fastened under the ground screw. This is under the end plate on the opposite side from the lead wire. Test for voltage with the top cover off, to determine if it shorted the terminal.