I lost another magneto coil

[biknut]

I'm still not sure what's going on with my magneto coils. This is the third or fourth one I've lost in a years time on 2 different motors. I'm losing count.

Each one has failed the same. The coil winding goes open. None of them had a bad solder joint. This tells me they all burned out.

The first 2 died within a few hundred miles of each other last summer when it was real hot outside. I was pretty sure a combination of high ambient air temperature, plus the stock kill switch shorting the coil wires together was probably the cause. This was just a guess though, and none of them actually failed when I hit the kill switch, now that I think about.

The symptoms are always the same. I'm always riding along at high rpm when the failure occures. The motor will studder a little, then will quickly get weaker and die. Testing reveals the coil winding to be open. A new magneto coil makes everything good again.

I attempted to stop this from happening by changing the kill switch from a momentary switch, to a single pole switch wired where it just opens the circuit to kill the ignition. This kind of switch doesn't short the coil wires together.

This latest failure happened on my newest bike at less than 200 miles. It's had the new style kill switch from day one, so it was never subjected to having it's coil wires shorted together even once. Plus it went into service in December so it's never seen high ambient temperatures either.

Sunday I rode it home from a long ride at over 7000 rpm for close to 20 miles. When it failed yesterday it was the next time I went riding after Sunday. It failed after about 5 miles, and shortly after getting up to high speed.

Lacking any better ideas, I guess the next thing I'll try is reducing my spark plug gap. I've been running 0.030". I'll try 0.024" for a while and see what happens.

I'm open to other suggestions.

 

[Kioshk]

I lost 3 in as many months...where are you getting yours from? My present one is about 2 weeks old; got it on eBay from BGF.

 

[biknut]

I lost 3 in as many months...where are you getting yours from? My present one is about 2 weeks old; got it on eBay from BGF.

2 that failed were stock Flying Horse coils. I have 2 BGF coils. I've also bought a couple from BikeBerry. At this point I can't really tell them apart.

I haven't noticed much difference between any of them. They're all about 350 ohms.

 

[Kioshk]

I've lost a few due to water-fouling...my last one just gave up the ghost after about two day's use. Like you, I lost it during an extended high-rev ride. I was "lucky" in that I had some carbon buildup in the chamber, and was able to continue riding to until I found civilization. I had actually received a replacement mag just that morning, so I had it on me fortunately. I'll have a look at the date-stamp on the last on that died. What's the date on yours?

 

[biknut]

I've lost a few due to water-fouling...my last one just gave up the ghost after about two day's use. Like you, I lost it during an extended high-rev ride. I was "lucky" in that I had some carbon buildup in the chamber, and was able to continue riding to until I found civilization. I had actually received a replacement mag just that morning, so I had it on me fortunately. I'll have a look at the date-stamp on the last on that died. What's the date on yours?

The one that just failed has 11.10.30 on it. I assume that's 2011, October, 30th. I bought the motor July 2012, and installed it December 2012.

None of failures were related to water. All of them seem to be high speed related.

I'm assuming the more rpm, the more current going through the coil.

 

[Kioshk]

No, I think that's November 10, 1930. That was a bad week for magnetos apparently; Great Depression related y'know.
I'll have a look at my stock and update here.

 

[biknut]

One other thing I've noticed lately that was probably a clue.

A few weeks ago I installed I wireless speedo. It's maker claims it to be very resistant to RF interference. After installing it I found that to be true. I never noticed any interference at any speed.

Then all of a sudden it started getting some interference starting, I think Sunday, or not more than one day before that. I only noticed it over 30 mph. I think that was a sign it was trying to tell me something when I started getting RF interference, and 2 rides later the mag failed.

Before the coil failed all together, it must have started getting noisy.

I'll be able to tell more after my next ride later today, now that I've replaced the coil.

 

[Wickedest1]

im staring at 4 dead mags with that same stamp on it...maybe its a bad lot because 2 came from bgf and 2 from bberry...strange biknut dont ya think...i kept thinking water damage but the last 2 havent even lasted a week a piece...this last one was from ebay but not bgf...all have that dreaded stamp and i didnt even bother to pay those stamps any attention until i saw this thread and read the posts...very strange

 

[biknut]

im staring at 4 dead mags with that same stamp on it...maybe its a bad lot because 2 came from bgf and 2 from bberry...strange biknut dont ya think...i kept thinking water damage but the last 2 havent even lasted a week a piece...this last one was from ebay but not bgf...all have that dreaded stamp and i didnt even bother to pay those stamps any attention until i saw this thread and read the posts...very strange

What's the time stamp on them?

 

[2door]

If you have some free time try disassembling(unwinding) the coil. I'd be very interested in seeing if the coil is failing internally. I suspect you're looking at a poorly isulated winding and the vibration is allowing the coils of wire to shake enough to shunt the winding.

Look for evidence of arcing where the current jumped between the wire or to ground against the core (laminated horse shoe shaped frame)

I have no idea what kind of amperage we're looking at being produced but the voltage is relatively low, somewhere under 100 volts at WOT. Usually around 80 volts nominal. If the guy winding the mag nicked the wire, damaging the insulation that coats the wire that can lead to premature coil failure, actually a short circuit, which could possibly burn a wire causing an open circuit.
I realize that unwinding a mag coil would be a labor intensive task but it might tell you where the coil is open and give some indication of what caused the failure. Think of it as doing an autopsy.

Are you absolutely positive about the solder joints being good? There have been several reported cases of broken solder joints or a broken wire at or near the frame. Some have not been obvious at a casual glance. Check them under magnification to be sure.
Let us know what you find if you tear one apart.

Tom

 

[Wickedest1]

biknut the only one of them that i can see is only the colon and 22...all the other parts are either too oily to see or just plain not there...ive sent an email regarding this to both bgf and bberry...have to wait and see now...maybe when i dont have a million things to do i will take the 2 hours to disassemble one...i may cause more damage than whatever small little whatever tho...results wont be conclusive

 

[biknut]

If you have some free time try disassembling(unwinding) the coil. I'd be very interested in seeing if the coil is failing internally. I suspect you're looking at a poorly isulated winding and the vibration is allowing the coils of wire to shake enough to shunt the winding.

Look for evidence of arcing where the current jumped between the wire or to ground against the core (laminated horse shoe shaped frame)

I have no idea what kind of amperage we're looking at being produced but the voltage is relatively low, somewhere under 100 volts at WOT. Usually around 80 volts nominal. If the guy winding the mag nicked the wire, damaging the insulation that coats the wire that can lead to premature coil failure, actually a short circuit, which could possibly burn a wire causing an open circuit.
I realize that unwinding a mag coil would be a labor intensive task but it might tell you where the coil is open and give some indication of what caused the failure. Think of it as doing an autopsy.

Are you absolutely positive about the solder joints being good? There have been several reported cases of broken solder joints or a broken wire at or near the frame. Some have not been obvious at a casual glance. Check them under magnification to be sure.
Let us know what you find if you tear one apart.

Tom

Tom, I did unwind one coil last summer. About a mile in, the wire was broken. I couldn't really tell by looking is it just broke, or was melted.

This coil that just failed, I can see where the wire comes out of the wrap at both ends. There's no continuity between those two points, so I don't feel the solder joint is an issue in this case.

I suppose vibration could be part of the reason, but this coil only has 200 miles at most, and this motor is pretty smooth.

A wider gap on the spark plug increases the voltage requirement needed to jump the gap, which in turn increases the current demand. Higher rpm also increases the combustion pressure, which again, increases the the voltage needed to jump the gap even more. I think that's the high rpm relationship. All that plus extended high speed running increases the heat that builds up in the coil. Heat probably degrades the insulation.

I'm hoping reducing the gap will help. I can't do much about the high speeds, I'm afflicted from an early age with speedsicitus, and wristlokupus.

 

[BigBlue]

Don't know the quality of the copper wire or the insulation that may be the problem. Make sure the coil is properly grounded by removing the varnish from the backside of the coil, as explained by Grubee: http://www.grubeeinc.com/USA/Magneto Mystery.html

Here's an article on possible issues that maybe causing the problem. Your spark plug wire may not be grounded at all times and maybe vibrating loose at high speeds and therefore the high voltage created by the CDI has no where to go and stays in the magneto coil, causing it to burn the insulation. http://lausonsmallengines.com/EngineAssemblies/LMH/magneto.htm

"While I’m ranting on coils, I’ll mention that one of the worst things you can do to a coil is turn an engine over with the spark plug wire disconnected. The magneto is generating tens of thousands of volts and with the spark plug wire disconnected and no easy path to ground, that energy is still going to want to go somewhere. With the insulation between the wires of the secondary winding of the coil having only a thin coat of insulation, the electrical energy will begin jumping the layers of the coil and burning through the insulation inside the coil. This, in time, will break down the coil and cause many shorts within the coil as part of the winding is short circuited. Eventually, the arcing within the coil will burn a wire through, causing a “open” or infinite resistance, or the coil will have so many “shorts” that it can no longer produce the required voltage to fire a spark plug. Either way, the coil is ruined and will need replaced".

By the way, you never stated if you had the original plug wire or replaced with an after market version. It would be interesting to know what the resistance value of a original wire compared to the after market. Possibility that plug wire itself may be the culprit.

Chris
AKA: BigBlue

 

[biknut]

I just went for a test ride after reducing my spark plug gap down to 0.025" from 0.030.

It started instantly. It could just be my imagination, but it felt like the bottom end was better. Top end seemed as good as before.

I still see RF interference above 30. It's possibly showing up more now because of the batteries getting lower than they were when the speedo was new. May not have much to do with the mag coil.

 

[Fugi93]

I just went for a test ride after reducing my spark plug gap down to 0.025" from 0.030.

It started instantly. It could just be my imagination, but it felt like the bottom end was better. Top end seemed as good as before.

I still see RF interference above 30. It's possibly showing up more now because of the batteries getting lower than they were when the speedo was new. May not have much to do with the mag coil.

Keep us posted on how that works out. This got me worrying when I am 20 miles out.

 

[biknut]

Keep us posted on how that works out. This got me worrying when I am 20 miles out.

I will. I have the same concerns, especially with Summer coming.

I have high hopes for this reduced plug gap.

 

[buba]

these kit magnetos certainly are fragile

especially after a high speed run

anyone able to rewind them with better material will certinly have a business!!!!

any taker able to do such a job???

 

[biknut]

I wonder if a rare metal spark plug would have less resistance, which might help the situation by lowering the voltage requirments?

 

[UVsaturated]

I seriously doubt coil failures are being caused by anything other than poor quality materials and/or workmanship of the coil windings and copper wire used. I have had many people say, it is vibration, or heat or this or that. The truth is, many things are substandard quality on these engines. This is a known fact, so why is it hard to imagine that the Chinese are only using poor quality copper wire for their coils?

The wire gauge is only .005" in diameter. If the gauge tolerance varies undersize by much it can cause a weak point in the wire where it cannot handle the electrical current flowing past that point. This could lead to a hot spot in the wire which can cause a pre-mature failure. Do you really think the Chinese use grade A wire for these coils? Did you know the cheapest I've seen 36 gauge wire on sale for here is about $25 for a 3000' roll. That will wind about 3 magnetos if I stand correct. That means that the Chinese are definitely buying cheap wire or making cheap copper wire.

Let me add, there is no failures inside the coil due to vibration. Maybe on a soldered joint that can move, but for all practical purposes the wire inside the winding cannot move and is not subject to vibrational failure or fatigue.

 

[biknut]

I seriously doubt coil failures are being caused by anything other than poor quality materials and/or workmanship of the coil windings and copper wire used. I have had many people say, it is vibration, or heat or this or that. The truth is, many things are substandard quality on these engines. This is a known fact, so why is it hard to imagine that the Chinese are only using poor quality copper wire for their coils?

The wire gauge is only .005" in diameter. If the gauge tolerance varies undersize by much it can cause a weak point in the wire where it cannot handle the electrical current flowing past that point. This could lead to a hot spot in the wire which can cause a pre-mature failure. Do you really think the Chinese use grade A wire for these coils? Did you know the cheapest I've seen 36 gauge wire on sale for here is about $25 for a 3000' roll. That will wind about 3 magnetos if I stand correct. That means that the Chinese are definitely buying cheap wire or making cheap copper wire.

Let me add, there is no failures inside the coil due to vibration. Maybe on a soldered joint that can move, but for all practical purposes the wire inside the winding cannot move and is not subject to vibrational failure or fatigue.

I don't think anybody will disagree with you. We all know the quality is very low. I feel the same way as you about the vibration. The coil is wound so tight I don't see how the windings could move.

Personally I think the problem is a combination of factors. Poor, inconsistant quality of the copper wire is one thing. Making the coil out of the thinnest wire possible to keep the cost down, and poor workmanship is another big factor. Then when you add to that, running at maximum output for extended time, it's easy to see why a coil would fail.

All we can do is try to understand what's happening and why, and then try to do what we can to make the coils life as easy as possible. Or at least try not to do anything that will increase it's load.