M20C Magnetos

[Arsobo]

Hi All, just bought a 64 M20C.

Mags are a little on the old side so I'm prepping to get them overhauled. However, when I took photos of the data plates I realized I have Bendix S4LN-204 on BOTH the left and right magneto.

The Lycoming parts catalogue calls for S4LN-200 on the left (Impulse coupling) with S4LN-204 on the right. Powerup Magnetos calls for the same in their compatibility chart. 

What is the correct arrangement for the M20C? I know we have a "starting vibrator" per the manual but I'm not sure what is supposed to be on the engine.

 

Thanks,

A

[LANCECASPER]

1 hour ago, Arsobo said:

Hi All, just bought a 64 M20C.

Mags are a little on the old side so I'm prepping to get them overhauled. However, when I took photos of the data plates I realized I have Bendix S4LN-204 on BOTH the left and right magneto.

The Lycoming parts catalogue calls for S4LN-200 on the left (Impulse coupling) with S4LN-204 on the right. Powerup Magnetos calls for the same in their compatibility chart. 

What is the correct arrangement for the M20C? I know we have a "starting vibrator" per the manual but I'm not sure what is supposed to be on the engine.

 

Thanks,

A

In the logs when were they last inspected by shop?

[PT20J]

The left magneto is used for starting and will either have an impulse coupling, or a retard breaker used for a shower of sparks (a.k.a. starting vibrator) system. According to the attached chart, the left mag should be a S4LN-200 for a shower of sparks system. (S4LN-21 for impulse coupled).

[markgrue]

Look at the tcds for the engine.  It uses a -200 and a -204

[Arsobo]

Thanks all, I did a deep dive last night.

SL4N-200 Left and SL4N Right is correct.

PN: 10-600614-1 and 10-600644-1 for anyone that searches this in the future are the correct "new" magnetos due to superseding part numbers. 

How I have the wrong magneto installed is beyond me - it starts and runs fine. Maybe the Data plate is wrong? Hopefully I can find a replacement SL4N-200 without getting bent over the barrel. 

Odd question for anyone, on the parts manual the drive gear (LW-72495) for the S4LN-200 is different than the S4LN-204 (LW-73683). However, in another manual LW-72495 drive gear was superseded by LW-73683 and now matches the S4LN-204 drive gear. Does anyone know if these gears are fundamentally different? Going to be another kick in the shorts to find another gear if needed. 

Edited 4 hours ago by Arsobo

[PT20J]

2 hours ago, Arsobo said:

Thanks all, I did a deep dive last night.

SL4N-200 Left and SL4N Right is correct.

PN: 10-600614-1 and 10-600644-1 for anyone that searches this in the future are the correct "new" magnetos due to superseding part numbers. 

How I have the wrong magneto installed is beyond me - it starts and runs fine. Maybe the Data plate is wrong? Hopefully I can find a replacement SL4N-200 without getting bent over the barrel. 

Odd question for anyone, on the parts manual the drive gear (LW-72495) for the S4LN-200 is different than the S4LN-204 (LW-73683). However, in another manual LW-72495 drive gear was superseded by LW-73683 and now matches the S4LN-204 drive gear. Does anyone know if these gears are fundamentally different? Going to be another kick in the shorts to find another gear if needed. 

Call Aircraft Magneto Service. They are very knowledgeable and may be able to take your -204 core in trade for a -200. Gears should be the same, but they will have the most current part numbers and you’ll get a magneto back good as new.