Magneto wiring

[nichzimmerman]

All,
I've been absent for 6 months on another project, but time to start turning wrenches on the Bearhawk again. Lots of new topics for me to catch up on, but I need some schooling on magnetos. I'm using toggle switches for the mags, and Aeroelectric Connections has a clever trick for ensuring you only have the impulse mag on when engaging the starter. That requires you to know if you have an impulse mag. How can you tell? The mags on my O-540 are Slick 6393 and 6350. The only indication I can find are sales listings that specify these models are non-impulse. The lag appears to be different on each. So, impulse or not? Where's the documentation? Thanks in advance.

mags.png

[jaredyates]

Zoom out and show us the whole mag. Is one longer than the other? The impulse coupling is about an inch thick and it is on the drive end between the engine and mag.

[BravoGolf]

Here is an image of an impulse coupling on a slick mag, shamelessly copied from the internet. Slick should have a maintenance manual for these, but if you look at the TCDS for your specific engine it will list the mags and the location L or R. One should have the impulse coupling mounted, I think it will be the 6393. You should also have a mounting “ring” that goes between the case and the mag covering the impulse coupling. That slides on the studs and then the mag with the coupling usually on the left side. Don’t forget gaskets.

i hope that helps

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[PaulSA]

The 6393 is a retard breaker, not an impulse. You will need a Slick Start unit as well for starting. The 6350 is a standard mag. Exactly the set up I have on my RV-10.

[PaulSA]

Sorry, was in a bit of a rush this morning, hence the very brief reply .....

The retard breaker has a second generator excited at start by the Slick Start unit. You will see an extra terminal on the 6393. As the name suggests, this is retarded with reference to the standard advance. Also, it is an electronic spark generator which gives a bigger bang than the impulse to aid starting. The downside is that you need ship's power to start and cannot hand swing. You power the Slick Start from the starter relay ("I" terminal, IIRC). The Slick Start comes with the necessary wiring diagram.

With this set up, I would recommend using a keyed ignition as you can then automate all the necessary inhibitions.

Cold, my RV-10 starts first or second blade. Hot starts are, of course, a bit more problematic!

[nichzimmerman]

Thanks all for the input. The engine I have is configured as removed from a Commanche. I didn't have the luxury of seeing how it was wired on the Commanche though. I'll get better pics next time I'm at the hangar.

[nichzimmerman]

Here are broader pics of the mags. Hard to get to now because it's getting crowded back there. The base of each look the same...it appears they both have an additional ring of some kind between the mag and the engine, vs the pics provides by Scott.

Paul, I have a hard time imagining the Commanche this came off had that slick start unit hidden in it somewhere. How reasonable would you think it would be to start a carb'd engine without that? If I have a hard time starting, I'd rather spend that money on a Surefly.

So, the engine starts on the mag with retard breaker only? I've already installed mag switches so would rather go with that vs keyed if possible.


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[Bcone1381]

Is is possible the Comanche had Shower of Sparks instead of an impulse coupler?

[BravoGolf]

It’s hard to say without pulling the mags. The images make it appear that both have an impulse coupling, which doesn’t make sense. The advantage to a keyed switch is its function of grounding the right mag during start to avoid kickback. However I use toggle switches and just don’t unground the second mag until after starting. What is the engine, can you tell us the year and serial number? As it came out of a certificated aircraft the TCDS might help.

EDIT I looked up the O-540/A1A TCDS and originally this model had S6LN-20 and 21 magnetos with a single impulse but both could have impulse couplings. There are alternate magnetos so this could become a bigger research project, check the logs and find out what was installed. It would probably be faster to pull the mags, of course you would have to retime them.

[PaulSA]

It is probable that the Commanche had "shower-of-sparks" - the Slick Start is basically a more modern electronic version. You don't show the connections in the photos. If your model numbers are accurate, then the 6393 has an extra terminal for the retard breaker. I don't believe either of these mags have an impulse coupling