Dual Mag woes

DesertNomad

DesertNomad

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DesertNomad
I have a D3000 Dual Mag. Yuck.

When I bought my Dakota, during a mag check I would see a drop of 70-80 on each side and smooth operation. Then, 50 hours later, my left mag nylon gear lost teeth. I sent the mag to Aircraft Electrical Components in Redding, CA for overhaul. When it came back the mag checks were the same... a drop of 70-80 and smooth on each side. It was that way for 500 hours.

Recently it was time for another 500-hour inspection. They did an overhaul as the cam and other parts were showing signs of wear. Two weeks ago we received the mag back from AEC but the drops were Left-80 and Right-150 or so. The timing was set to 20R/23L. It went back to AEC and we got it back this week. Now the drops are Left-50, Right-100 which is just barely within spec. The timing is 22R/23L.

I am concerned that the drops are so uneven. The mag shop says it may be getting bounced around in shipping. The shop says it is very difficult to get back on with all the clamps and such and is reluctant to take it off again - we don't want a maintenance-induced failure.

I have already spent way too much with my shop on sorting this all out.

Would this drop/difference concern folks here?

I don't know what to do next. I am in Reno, NV and my plane is in Portland, OR.
 
DesertNomad said:
The timing is 22R/23L.
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IIRC there's a 2-degree tolerance for the timing, and that setting should be fine. I would be more concerned with the internal timing of the mag, something the mechanic can't get at easily and that takes a great deal of patience to correct in one of those things. Special tools help. If the internal timing is off, the points aren't opening at the correct position of the rotor and the spark is weak, which is what I'd suspect for the side with the larger drop.

Broken nylon gear teeth is usually caused by using a locking tool forbidden by TCM/Bendix. It's used to hold the mag gearing in a certain position for getting the mag-to-engine timing right. A pain without the tool, a risk with it. No fun.
 
The timing is in spec but like Dan mentioned, I suspect the internal timing may not be as good as it could be. These magnetos are challenging to work on but with patience they are no big deal.

What all was sent out for service? Did the capacitors get replaced?
 
Yes, I believe the capacitors did get replaced. We also replaced the ignition harness, but not the spark plugs (Tempest fine-wire).
 
Warning: a total WAG.

Swap top and bottom plugs on all cylinders and see if the drops swap? If they do, swap half the cylinders back. From there, swap them one at a time. This *might* localize a problem cylinder.
 
DesertNomad said:
Yes, I believe the capacitors did get replaced. We also replaced the ignition harness, but not the spark plugs (Tempest fine-wire).
Click to expand...

Is the right magneto consistently the one with problems?
 
Electroair is working on a certified solution. But that doesn't help you here. Really does suck how your pigeonholed into that. If it were something on a car it probably would have been recalled
 
I'd like to go electric but need a second power source - battery or alternator. I have room for a second alternator via the now empty vacuum pump port. I don't want to be their first customer though as I'd rather see how it goes for a few years.
 
DesertNomad said:
Yes. The first time AEC sent it back we saw a drop of 70L/130R and the second time a drop of 50L/100R (right at the edge of acceptable).
Click to expand...

Try replacing the right capacitor or switching them side to side.
 
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