Magneto Woes

[Graueradler]

The right mag (non-impulse) died on my Cherokee today. Engine RPM would initially drop about 500 RPM while bucking and backfiring. If the switch was left in that position, the engine would die fairly quickly. It was working fine on two earlier flights today. I haven't done anything with it yet but park the plane. It is a Slick 4200 series. Replacement seems to be a 4370. I'm tempted to just bite the bullet and buy a new one (~$500 if I get credit for the core) but I guess I at least need to look at this one first. Maybe it is something easy to fix. Problem must be electrical and not mechanical since it is obviously still generating some spark at near the proper time. What do you expect I'll find when I open it up? Replacing points, coil and condensr would take care of just about any elctrical problem but then I'm a good way toward the cost of a new one and still have a pretty old mag mechanically.

 

[Michael]

Sounds alot like my mooney when the plugs get fouled. Did u run it real lean for a while at runup speed? That usually clears mine up. I thought when the mag went, it goes. nothing left.

 

[Tom-D]

I thought when the mag went, it goes. nothing left.

Not always. but most of the time.

carbon tracking on the distributor block can cause a bunch of missing and back fireing.

 

[Graueradler]

Sounds alot like my mooney when the plugs get fouled. Did u run it real lean for a while at runup speed? That usually clears mine up. I thought when the mag went, it goes. nothing left.

I didn't try that because when I've had a fouled plug before, I got rough running and an RPM drop but not like yesterday and no back firing. Since it seemed different, I just assumed it was the mag. I keep a spare set of 4 spark plugs in the plane with tools for changing them out. I'll try that first today before pulling the mag.

 

[Tom-D]

I didn't try that because when I've had a fouled plug before, I got rough running and an RPM drop but not like yesterday and no back firing. Since it seemed different, I just assumed it was the mag. I keep a spare set of 4 spark plugs in the plane with tools for changing them out. I'll try that first today before pulling the mag.

Save your time and energy, pull the mag.

 

[Graueradler]

Save your time and energy, pull the mag.

You were right (as usual). I did change the plugs and the result was still unacceptable. I fully expected it to be but its easier to change plugs than to re-assemble the mag, re-install it and time it. It ran better this morning than yesterday but yesterday, the engine (and mag) was already hot. This morning it was a cold start. I took the mag apart and other than carbon and posssibly low spring force on the points, I could see nothing wrong. I cleaned up the carbon with q-tips and alcohol, cleaned the points with some 600 paper and increased the spring force just a tad. I'll take it back to the airport tomorrow and see if that did it. This mag has consitently had a greater drop than the other one.

 

[Henning]

You were right (as usual). I did change the plugs and the result was still unacceptable. I fully expected it to be but its easier to change plugs than to re-assemble the mag, re-install it and time it. It ran better this morning than yesterday but yesterday, the engine (and mag) was already hot. This morning it was a cold start. I took the mag apart and other than carbon and posssibly low spring force on the points, I could see nothing wrong. I cleaned up the carbon with q-tips and alcohol, cleaned the points with some 600 paper and increased the spring force just a tad. I'll take it back to the airport tomorrow and see if that did it. This mag has consitently had a greater drop than the other one.

Even with 600 sandpaper, your points won't last now. If you haven't assembled yet, polish the points. I use a matchbook cover to clean points (BTW, in a pinch you can also use it to set them).

 

[gismo]

Even with 600 sandpaper, your points won't last now. If you haven't assembled yet, polish the points. I use a matchbook cover to clean points (BTW, in a pinch you can also use it to set them).

I thought that points were plated with a thin layer of something real hard and that any "sanding" would cut through that and leave you with really short lived ones whether or not you polished the result. I used to have a contact "burnisher" that was used to polish light corrosion on points. Of course if there is serious corrosion or pitting nothing but a new set will be much help in the long run.

 

[Graueradler]

Burnished the points with a regular burnishing tool. Put it all back together and got an acceptable run-up. I'll move it back to home base tomorrow and check again after it is hot. If the troubles return when it is hot, would that be an indicator of a bad coil?

 

[Henning]

Burnished the points with a regular burnishing tool. Put it all back together and got an acceptable run-up. I'll move it back to home base tomorrow and check again after it is hot. If the troubles return when it is hot, would that be an indicator of a bad coil?

Possible, also possible bad condensor. Were the points pitted? Typically pitting is caused by a bad condensor and they can have a bad effect on the running as well. You may still need to replace the points if this is the set you took the 600 to, typically they don't last long after you sand them.

 

[zephyr]

The right mag (non-impulse) died on my Cherokee today. Engine RPM would initially drop about 500 RPM while bucking and backfiring. If the switch was left in that position, the engine would die fairly quickly. It was working fine on two earlier flights today. I haven't done anything with it yet but park the plane. It is a Slick 4200 series. Replacement seems to be a 4370. I'm tempted to just bite the bullet and buy a new one (~$500 if I get credit for the core) but I guess I at least need to look at this one first. Maybe it is something easy to fix. Problem must be electrical and not mechanical since it is obviously still generating some spark at near the proper time. What do you expect I'll find when I open it up? Replacing points, coil and condensr would take care of just about any elctrical problem but then I'm a good way toward the cost of a new one and still have a pretty old mag mechanically.

4200 series Slick coils are notoriously bad. Don't bother to fix it unless you replace the coil. The real fix is the 4370. Charlie Melot Zephyr Aircraft Engines

 

[gismo]

4200 series Slick coils are notoriously bad. Don't bother to fix it unless you replace the coil. The real fix is the 4370. Charlie Melot Zephyr Aircraft Engines

I've got a 4230 that appears to have a bad (heat sensitive) coil. Works fine for a while after startup but starts to miss once it gets heat soaked from the engine. A replacement 43xx just arrived from Aircraft Spruce and will be going on the plane soon. Hopefully the other mag won't suffer the same fate soon. The current ones have something like 1000 hrs on them spread over 25 years so I guess I'm due, but at close to $600 each, it seems a bit pricey.

 

[Graueradler]

Well, it must be a bad coil. I flew back to my home base today. Good mag check pre-takeoff, perfect mag check (couldn't tell any difference between left and right and totally smooth) in the air near destination (20 mile flight) and total failure on the ground when I got ready to shut it down. The right mag was totally dead. I'm think I'm headed for putting a new 4370 in it.

 

[Graueradler]

Just ordered a new 4370.

 

[Graueradler]

Installed the new mag today. Runup was great )both mag drops nearly identical, right mag has always been worse that the left mag before, plus static RPMs were higher than I've ever seen. In the past, I've been seeing 2300, sometimes a little more, maybe 2320. Today with the new mag, it was 2340-2350. Unfortunately, while I'm doing this testing, I noticed fuel stains on the side panel below the tank selector valve.