Polarity of the battery is not important. Miscellaneous: Chassis box 3-inch by 4-inch by 5-inch, rubber grommet for lamp and wires, test leads, alligator clips, battery box, terminal strip.Īssembling Components Assemble the components according to the schematic drawing. Operates on about 60 volts AC.īuzzer: 3- to 6-volt door buzzer, vibrator-type (Sears, Roebuck “Dixon”).īattery: 3 to 6 VCD use two or four D-cells in series, adjust buzzer to suit voltage. Lamp: NE-51H neon lamp or any 125th watt such as NE-2, NE-48 or NE-51 without resistor. Transformer: Table radio (tube-type) speaker output transformer, 5-watt, 3,500 ohm/3.2 to 4 ohms. Necessary components These timers are available commercially from aircraft tool supply houses, but a suitable box may be simply constructed from materials often found in the well-equipped engine buff’s shop. Aircraft buzz boxes have two little lights to allow simultaneous timing of the two magnetos, but since this is not needed for a single ignition engine, the plans show how to build a one-magneto system timer.

The buzz box allows the mechanic to accomplish this quickly and accurately. Virtually all piston aircraft engines use dual magneto ignition, and the magnetos must be properly timed, both internally and to the engine. While this may be accomplished by the old-time technique of placing a bit of cellophane between the points and noting the position of the timing mark at the time of the release of the cellophane, there is an easier and more accurate method: the aircraft mechanic’s electronic magneto timer or ‘buzz box.’ Both types of timing depend on knowing exactly when the points open.

For the engine to run properly, this hot spark must occur at a certain time in the piston’s travel, usually several degrees before top dead center.

The onset of breaker point opening at E-Gap determines the final point gap setting. E-Gap is usually found by the alignment of marks on the gears inside the magneto or by a degree measurement made with a special fixture. For the hottest possible spark, the points must open exactly at the magnetic neutral, or ‘E-Gap’ position of the armature.

In the high-tension magneto, the spark occurs when the breaker points open, just as it does with a coil and battery system. This isn’t a particularly difficult job, but it can be made a little easier with the right tools and a bit of understanding. Every so often, we read someone’s request for help in timing a magneto to their engine.

Magneto timing light circuit