Right mag quit working

[EricJ]

On 4/9/2018 at 6:38 AM, M20Doc said:

The early J models had the ignition switch wires the same way as late F models, in that the right P lead was grounded during start.  S/I M20-59 gave instructions for removing the grounding jumper at the switch, thereby allowing both mags to fire all spark plugs.  I’ve encountered several that were not modified.

Clarence

I thought the point of disabling the non-Impulse-Coupled magneto was to allow the IC to retard the timing for slow rpm start, as the relatively advanced timing on the magneto might result in enough preignition at slow rpm to interfere with starting.

The Cub I got my tailwheel endorsement in just had two switches and I used to start it with both on, but it'd occasionally stop the prop dead during start.   Starting with only the IC mag enabled was a lot smoother.

Am I missing something on the above case where that wouldn't be an issue?   Is the dual mag built differently?

 

[Guest]

1 hour ago, EricJ said:

I thought the point of disabling the non-Impulse-Coupled magneto was to allow the IC to retard the timing for slow rpm start, as the relatively advanced timing on the magneto might result in enough preignition at slow rpm to interfere with starting.

The Cub I got my tailwheel endorsement in just had two switches and I used to start it with both on, but it'd occasionally stop the prop dead during start.   Starting with only the IC mag enabled was a lot smoother.

Am I missing something on the above case where that wouldn't be an issue?   Is the dual mag built differently?

 

The D2000/3000 series magneto on early J models has only one impulse coupling for both magnetos and therefore no need to ground the right magneto during start, unlike other engines with independent magnetos with single impulse or SOS, where the right magneto is grounded during start to prevent kickbacks.

Clarence

[EricJ]

Just now, M20Doc said:

The D2000/3000 series magneto on early J models has only one impulse coupling for both magnetos and therefore no need to ground the right magneto during start, unlike other engines with independent magnetos with single impulse or SOS, where the right magneto is grounded during start to prevent kickbacks.

Clarence

Aha!  I didn't know the impulse coupler fed both sides, which is an interesting advantage of the dual magneto.   Now the Service Instruction makes sense.   Thanks!
 

[Guest]

Just now, EricJ said:

Aha!  I didn't know the impulse coupler fed both sides, which is an interesting advantage of the dual magneto.   Now the Service Instruction makes sense.   Thanks!
 

Those who go from an A3B6D engine to a A3B6 would either have to install 2 impulse coupled magnetos, or install the jumper on the ignition switch.

Clarence

[bradp]

Ok that makes total sense Clarence. 

[N201MKTurbo]

I just talked to Select Aircraft. It turns out that a bushing came loose on the right mag that allowed the distributer to slip out of timing.

 

BTW, even though it had been 4 years sense he overhauled it, he gave me a very good discount on the repair because he was the last one to work on it.

Edited April 16, 2018 by N201MKTurbo

[DonMuncy]

3 hours ago, N201MKTurbo said:

BTW, even though it had been 4 years sense he overhauled it, he gave me a very good discount on the repair because he was the last one to work on it.

That sounds like Aaron. He is a real standup guy.

[chrisk]

Nice to see its getting sorted out.