Garmin G3X RPM erratic issue after Bendix Dual Magneto D4LN-3000 / 10-682555-11- 500hrs inspection.

[Shawn26]

1 hour ago, Thedude said:

Any update on this?

I received good news yesterday from the Avionics Shop.

Last week, we removed the magneto and sent it to the mag shop for another inspection. They replaced the contact and bearing, both of which were already replaced during the 500-hour inspection. I reached out to Savvy Aviation for advice, and they confirmed that the only likely source of the erratic RPM readings (based on the P-lead signal) was the magneto creating an arc from the point, bearing and conatct. The mag shop recommended reinstalling the magneto, and if the issue persisted, they offered to build a new magneto from scratch to help rule out potential causes during the troubleshooting process.

After reinstalling the magneto, the problem remained. The Avionics Shop, frustrated after chasing the issue for so long, decided to install a new Garmin GEA24B. The erratic RPM readings disappeared and we have a good reading. According to Garmin, the GEA24B has better noise filtration than my previous GEA24A. 

I haven't picked up the airplane yet, but I trust their diagnosis. This process was extremely time consuming, labor-intensive, and expensive. My main concern is what will happen during the next 500-hour inspection. If I receive a noisier magneto, I’m not sure if the GEA24B will be able to filter out the distortion, potentially putting us back to square one. It's something to consider for the future.

[EricJ]

I just had my dual mag out for 500-hour inspection.    Prior to removal I had noticed that I could hear the ignition on my #2 radio when I was monitoring 121.5.    After reinstalling the mag after the 500-hour service the ignition noise is gone.   I did not replace the condensers (yet, although I ordered two new ones, long story), so it really was just the mag service that cured it.  If you get continued problems after getting a fair amount of time on the mag, maybe try a different mag shop.   My understanding is that the dual mags are a little tricky to set up compared to individual mags.

[PT20J]

I wonder if installing a filter between the mag switch and the GEA 24 would help.

https://lonestaraviation.com/product/faa-pma-magneto-filter/?srsltid=AfmBOor0hZYMZBEybv-zcpTVcfLp-qrsMUAFTVDflHqFtFddXQJYZnmJ&v=28886f13f578

[Shawn26]

2 hours ago, EricJ said:

I just had my dual mag out for 500-hour inspection.    Prior to removal I had noticed that I could hear the ignition on my #2 radio when I was monitoring 121.5.    After reinstalling the mag after the 500-hour service the ignition noise is gone.   I did not replace the condensers (yet, although I ordered two new ones, long story), so it really was just the mag service that cured it.  If you get continued problems after getting a fair amount of time on the mag, maybe try a different mag shop.   My understanding is that the dual mags are a little tricky to set up compared to individual mags.

This is my third time using Arrow Accessories for the magneto repair. I never had issues with their service. I know QAA also repair Bendix Dual mag. Beside these two I don’t know any other shop! Who did you use for your magneto? 

[Shawn26]

26 minutes ago, PT20J said:

I wonder if installing a filter between the mag switch and the GEA 24 would help.

https://lonestaraviation.com/product/faa-pma-magneto-filter/?srsltid=AfmBOor0hZYMZBEybv-zcpTVcfLp-qrsMUAFTVDflHqFtFddXQJYZnmJ&v=28886f13f578

That is something that I can ask my avionic shop. 

Edited March 6 by Shawn26

[EricJ]

11 hours ago, Shawn26 said:

This is my third time using Arrow Accessories for the magneto repair. I never had issues with their service. I know QAA also repair Bendix Dual mag. Beside these two I don’t know any other shop! Who did you use for your magneto? 

There are a lot of shops that will service dual mags these days.   I keep hearing that Aero Accessories in Van Nuys is good:

http://aeroacc-vny.com/ 

Mine was just service by Air Power Accessories in Camp Verde, AZ:

http://www.airpoweraccessories.com/