Mag timing

[Rjfanjet]

Quick question. I removed both mags for the 500 hour inspection. Left mag is a slick 4347. Other is a 4370. One data plate says 25 degrees, the other says zero. My mechanic is a little concerned with the zero. 

Lycoming O-360-A1D, shower of sparks. No impulse coupling.

[RLCarter]

Isn’t the 0° for the retard points?

[Rjfanjet]

So wouldn’t both be 25? Or do I actually set the timing for that mag at 0?

[N201MKTurbo]

Without the retard breaker, the magneto can be timed anywhere. With the retard breaker there is a timing difference between the points. You want the retard breaker to fire at TDC so the engine doesn’t kick back when you start it. If you time a 25 degree mag to 20 degrees, it will fire at 5 degrees after TDC which will have very little starting power. If you time a 20 degree mag to 25 degrees, it will fire at 5 degrees before TDC and may kick back if the engine isn’t turning fast enough.

The zero degree mag is the one without the retard breaker points, the 25 degree mag is the shower of sparks mag.

[carusoam]

Fantastic mag timing details Rich!

Thanks for sharing all of that.

Best regards,

-a-

[Rjfanjet]

Thank you for the info!