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E-Mag rebuild #2 in 50 hours

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werxcv01

Well Known Member
Returning from AirVenture, I had some mag trouble so left my -8 with St. Charles Flying Service at KSET and rented a car for the rest of the trip to Mississippi. I will admit to not remembering which key position selected which mag. I’ve had the aircraft for 2 years now (O-360, an aviation mag powering the aviation plugs on the bottom cylinders and an E-Mag powering the automotive plugs on the top cylinders) and every time I checked the magnetos it always seemed that the first key turn to the left resulted in less of an RPM drop than the second key turn to the left, so I had in my mind that the first key turn was the E-Mag. I had overnighted in Davenport Iowa on Saturday night after leaving Oshkosh in the mad rush to depart Saturday morning when the field finally went to marginal VFR. I had the airplane hangared at Davenport so I could depart early Sunday morning and not worry about a wet cover. On run up, I had low rpm of about 1450 on one mag. I assumed that there was lead buildup on the spark plugs so I went through the process of burning it off. That took a few times but I was finally able to get two consecutive good mag checks, so I took off. Cruising at 8500 feet I noticed an RPM drop of about 150. I went to full rich and checked carb heat, but I did not think about checking the magnetos. The RPM returned to normal but I had already started my descent to St. Charles. The Director of Maintenance happened to be there that Sunday morning so he cleaned, tested and gapped the lower aviation plugs but they all checked out fine. He then opened the front of the aviation magneto and we found a trace of oil in the case. Thinking we had found the problem, he had the magneto shipped off to be checked out. The magneto had last had the 500 hour inspection about 125 hours earlier, but they did find a missing tooth on one of the gears and the condenser was old and needed replacing. However once it was reinstalled, the engine still ran rough, apparently because of the E-Mag. Troubleshooting that, they determined that two of the automotive ignition cables were bad. Once they replaced those they determined that possibly the coil was bad. They replaced that but it is still not running smoothly. As of today they are sending the E-Mag back for the factory to look at. All the time that they were diagnosing the E-Mag they were talking to the company service rep, who suggested that the bad ignition cables could have caused a problem with the magneto.

This magneto was rebuilt less than 30 hours previously because I made the mistake of turning on the master while a battery charger was hooked to the Odyssey battery. There is another thread here covering that.

I am now wondering if I should consider a different magneto. I had previously thought to replace the aviation magneto with a second E-Mag, but now I am not so sure.

Any thoughts on why the bad ignition cable would have affected the magneto? Any suggestions for the most efficient way to get my airplane flying dependably?
 
Couple of thoughts/questions….
1) It sounds like you aren’t the builder, so the first question is - do you have an E-Mag or a P-Mag? The E-Mag was the early product of EMagair (the company), and it has been placed by the P-Mag, which is self generating. The real significance is that if you have an actual E-Mag, it is very old, and the older design….
2) Plug wires do go bad - usually, it is corrosion on the ends. Replacing the cable should solve the problem, but I think there is a possibility that running with a really bad cable for some period of time might end up giving you a bad coil. Someone smarter than me will likely chime in.


Paul

Full Disclosure - I currently have FOUR Lycomings with dual P-Mags, and they just work …. One early on failure that was fixed, and a couple of plug wire replacements in several thousand hours of operation.
 
No, I am not the builder.

Sorry for not being clear, but it is a P-Mag, with the built-in alternator.

BTW, I enjoyed getting to visit with you in the HBC pavilion the weekend before AirVenture started. I wanted to get by to pick up a copy of your book, but as is typical for my visits to AirVenture, there were too many things to do and not enough time for them all.
 
The first key turn to the left causes very little drop probably means that you are grounding the magneto, and the engine is running on only the Pmag, providing very little rpm drop.

Why would your newly rebuilt magneto have a broken tooth? Who rebuilt it the first time?

How does turning on the master switch while a battery is being charged damage a magneto? There’s no reason for that to happen..
 
How does turning on the master switch while a battery is being charged damage a magneto? There’s no reason for that to happen..

Unless there is something wonky in the wiring.

A properly set up mag is not effected by either the master switch or charging the battery.
 
Regarding the P-Mag being damaged by a battery charger, see my earlier thread at https://vansairforce.net/community/showthread.php?t=192972

Their service documents note that the P-Mags are susceptible to damage from battery chargers.

To clarify, the broken tooth was found on the aviation magneto. I don’t know why it passed inspection 200 hours ago. I was not the owner at that time.
 
Epilogue: My RV-8 and I left AirVenture 2021/KOSH on Saturday, July 31, and finally arrived at our homebase in Raymond, Mississippi together on Saturday, August 28. She spent a few weeks with Clint and the great folks at St. Charles Flying Service at KSET while they diagnosed and repaired both mag problems. The aviation mag was shipped off and a gear and condenser were replaced. The ignition cables and the coil on the P-Mag were replaced, then E-Mag graciously repaired the P-Mag gratis, since they had to do the same for me earlier this year at my cost.

Clint was complimentary of the customer service they received from E-Mag, and I really appreciate E-Mag for standing behind their work.

If you need service for your RV in the St. Louis area, check out St. Charles Flying Service at KSET.
 
Let's see: they rebuilt the mag, and that did not fix it; they found some bad wires, and that did not fix it. Then they sent e-mag for rebuilt because they don't know what else it could be? There are rarely multiple problems causing one symptom. Did e-mag say they found a problem, or did they just go through and do a standard service? My guess is that the shop broke the tooth on your magneto inspecting it. If the magneto was not working properly the aviation plugs would have been fouled.
I am not following what the problem was - a 150 RPM drop? For how long? You said it returned to normal. You can loose 150 rpm in a slight climb (FP I assume?) I would not have let the shop touch it until you established that there was a real problem.
 
Let's see: they rebuilt the mag, and that did not fix it; they found some bad wires, and that did not fix it. Then they sent e-mag for rebuilt because they don't know what else it could be? There are rarely multiple problems causing one symptom. Did e-mag say they found a problem, or did they just go through and do a standard service? My guess is that the shop broke the tooth on your magneto inspecting it. If the magneto was not working properly the aviation plugs would have been fouled.
I am not following what the problem was - a 150 RPM drop? For how long? You said it returned to normal. You can loose 150 rpm in a slight climb (FP I assume?) I would not have let the shop touch it until you established that there was a real problem.

The real problem was that one mag was only making 1450 RPM on the ground.

1) The mechanic removed the cap from the aviation mag in my presence and we saw oil in the case. He then removed the mag and shipped it off for repair, so there was obviously an issue with that mag not caused by the mechanic.

2) Once the aviation mag was re-installed and the aircraft tested, it became obvious there was an issue with the P-Mag only making 1450 rpm. Initial troubleshooting on that mag was that two cables were bad, so they were replaced. Discussing this with E-Mag, the troubleshooting indicated a bad coil, which was then replaced, but did not fix the problem. Then E-Mag recommended sending the P-Mag in, which they fixed and returned within 4 days.

3) The 150 RPM drop in level cruise at 8,500, autopilot and altitude hold engaged, was only a symptom. Once I landed at KSET (400 miles from my home base), I was getting only 1450 on the right mag. As I noted in my first post in this thread, I was thinking the right mag was the aviation mag, so my confusion led both the mechanic and me to check out the wrong mag, which obviously had an issue, just not the one causing the problem.

Again, I'm 400 miles away from home with an aircraft with an ignition problem that I don't want to fly. The mechanic went out of his way on a Sunday morning to help diagnose the problem, then drove me to two different car rental locations so I could get back to work by Monday morning.

I stand by my appreciation of the shop and the mechanics who worked on my airplane. I now have a flying aircraft at a cheaper cost than flying my own mechanic up for the work, or removing the wings and shipping the airplane to my hangar.
 
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