Magneto Timing Outside Limits

Having problems getting the magneto timed perfectly to the engine? Does it seem as though you cannot adjust the mag on the engine to get the points to break at the correct engine timing? You could have the wrong gear(R22) or coupling(R44) installed on the mag.


Robinson R22/ Lycoming O-320/ O-360

R22 Single Cut Keyway Gears
72495 and 61163

With single cut keyway gears you must install the correct gear on the correct mag, and not all gears are marked with part numbers for easy identification. The following pictures will help you to install the correct gear on the correct magneto.

Left/ Retard Magneto



Gear P/N 72495

Right/ Tach Point Magneto



Gear P/N 61163

R22 Double Cut Keyway Gears

Double cut keyway mag gears can be more confusing upon install, because it is easy to get the gear installed 180 degrees out and not know it untill you install the mag and try to time to the engine. The following pictures will help you to positively install the gear correctly per your part number magneto.

Left/ Retard Magneto Keyway Position

Right/ Tach Point Magneto Keyway Position

Robinson R44 Raven I / Lycoming O-540-F1B5

Ignition Timing Set to 25 Degrees BTDC

S6LSC-200 (Retard/ Left Mag)



Install Drive Coupling 

P/N 73013

The O-540-F1B5 Retard/ Left Mag is P/N 10-600616-3, which has a 37.5 degree housing and the retard contacts are set to open 37.5 degrees after the run set of contacts open. To correctly time this mag to the engine us must use the P/N 73013 Drive Coupling.

S6LSC-204T (Tach/ Right Mag)



Install Drive Coupling

P/N 73000


Both the O-540-F1B5 and the IO-540-AE1A5 use the same P/N

10-600646-201 Tach/ Right Mag, however it is they DO NOT use the same P/N Drive Coupling. The O-540-F1B5 Drive Coupling is P/N 73000.

Robinson R44 Raven II / Lycoming IO-540-AE1A5

Ignition Timing Set to 20 Degrees BTDC

S6LSC-200 (Retard/ Left Mag)



Install Drive Coupling P/N 73000

S6LSC-204T (Tach/ Right Mag)



Install Drive Coupling P/N 73636

The IO-540-AE1A5 Retard/ Left Mag is P/N 10-600616-9, which has a 30 degree housing and the retard contacts are set to open 30 degrees after the run contacts have opened. This mag requires the Drive Coupling P/N 73000.

The IO-540-AE1A5 Tach/ Right Mag is P/N 10-600646-201 the same as the O-540-F1B5 however in the IO-540-AE1A5 install Drive Coupling P/N 73636.

Test, Repair, Inspect and Overhaul Bendix and Slick aircraft magnetos


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