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Rough runner and Pmags

exercise

Well Known Member
Hi Guys,
During the second flight in a week, my recently rebuilt(90 hours) Lyc 320 E2A , dual Pmag, Airflow Performance Bendix FI, 8.5 pistons, engine started running rough after about 10 minutes after level off at 3500'. Temps and pressures were all ballpark while I varied prop, throttle, mixture, fuel tanks (fresh mogas in one and fresh 100LL in other) and altitudes with no improvement. WH???

I'll cut to the chase so once I landed back at home, I called Bill Repucci of EI Commander. He walked me through a few pages of the EIC I have installed and with that information, he suggested that my rough runner was either a bad pmag shaft bearing or a bad mag gear. This all happened within 30 minutes
of getting back to the hanger. I pulled both pmags and saw that one of the pmag gears was loose.

How and why the castle nut became loose after 90 hours of flying will be explained in the next thread I submit but this one is to offer my opinion that anyone that flies with Pmags would be well off having an EIC in the cockpit and the accompanying outstanding service that Bill R provides.
 
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Pmag gears

Hi Guys,
To continue with the recent rough runner thread, I brought the two Pmags to a very reputable aircraft repair facility in my area with the thought of replacing the old gear I had pulled off a traditional magneto. The shop owner brought out two new gears with the same part # as my loose one and it turns out that all three had shafts too long. The result was that they just barely touched the Pmag back wall and a perfect tapered fit was unable to be had. After 90 hours, the castle nut therefore became loose. The other gear I had installed was also the same part # but with a shorter shaft that did not reach the Pmag back wall.

Lycoming tech said that magneto gear 68C19622 has gone through multiple revisions due to different manufacturing processes/product improvements and they will all fit great on standard mags.

It makes sense that the Lycoming part # is designed specifically for the magneto used on the Lyc engines and only on those mags. It's not their problem if it doesn't fit the Pmag shaft.

Brad at Emagair said that he has encountered only a very few(maybe 3) gears that customers had had problems with. Page 2 of his manual mentions that 'The back wall of the accessory case will be close to the end of the shaft.' I missed that. He may in the future highlight this potential problem in a manual change or service bulletin.

My suggestion is to check for gear shaft clearance from the back wall during your next Pmag inspection.
 
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Johh, your posts are timely. I have dual PMAGs on my IO-390. I was climbing out this afternoon passing through 11,000 MSL when I got a rough running engine. CHTs were normal and EGTs were lower than normal. A quick ignition switch mag check verified that left ignition is malfunctioning. I landed uneventfully and will inspect the PMAGs tomorrow morning. I'll look for the internal gear issue you mentioned. Who knows, it could be fouled plugs too, but I think it felt more like a bad magneto.
 
My suggestion is to check for gear shaft clearance from the back wall during your next Pmag inspection.

John, to be clear, the clearance problem is between the p-mag body and the gear, not gear to crankcase wall? At the red arrow?
 

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I’d like to figure this out too. doing the startup LED test I’m getting flashing yellow which indicates a sensor magnet range check failure. The gear and shaft look and feel just fine. Is there anything left to do but remove the unit and send it in?
 
I’d like to figure this out too. doing the startup LED test I’m getting flashing yellow which indicates a sensor magnet range check failure. The gear and shaft look and feel just fine. Is there anything left to do but remove the unit and send it in?

After your first post, I was going to suggest that if a P-Mag suddenly starts running rough, the first thing I’d check for is a disconnected plug lead- at either end (the P-Mag or the plug).

But if you’re getting a flashing LED - I think you need to call Brad!

We’ve got three airplanes with dual P-mags (the fourth is in the process of being converted now during an engine overhaul), and in the ten or so years we’ve been flying them I’ve had ONE case where the P-Mag failed the sensor check at start-up And then it turned itself off (on the ground, before the run-up) because of that failure. It was the very old software, and that has been changed, so I’m not sure how the failure manifest itself these days.

Paul
 
Very early on, I had a rough-running engine (Dual P-Mags) and discovered that it was due to loose wire terminal screws on the factory installed blocks.
 
Thanks guys. I checked all harness ends secure, terminal blocks secure, wires inside the terminals secure. I pulled the PMAG and there's no unusual movement in the shaft, and rotation is perfect. Drive gear condition is perfect. But the flashing yellow LED really says it all. It's failing the Sensor Magnet Range Check per p. 24 of the manual. It's a failed PMAG, no way around that.

I did notice that the inside of the #1 harness post on the PMAG was burned, black and sooty. I can't figure that out. The harness is new, passed a resistance check this morning, no cuts, etc. But something caused the PMAG harness post to turn black.

This PMAG is fairly new. Less than one year old and has 170 hours on it. I just got off the phone with Brad at Emagair. What a great guy--totally stands by his product and will bend over backwards with the warranty repair. I am stranded in Provo, Utah though until I can get a new one shipped in. General aviation is an adventure, that's for sure!
 
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Hi Dan,
Your diagram showing the space we want to see is exactly what we want to see and I'll attempt to also upload my first photo to this message as well.
 

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