Post if your magneto failed due to moisture

I know not all are really interested in some very fine details of failure, but seems that if you’re going to dissect a failed part after ordering a new one already I want to mention this.

Seeing the part of your post where you write: “(but I do take a look at the soldering to ensure it hasn't been compromised from vibrations.)”

I know that vibrations on a cold (bad) solder joint make possible intermittent failures or even sold failures that are easier to diagnose, but one type of cold solder is one I never thought could happen.

I learned a while ago a soldered terminal post, just like on the old through hole circuit board component were mounted, can be insulated to a point that there is no connection if the rosin flux from the work make a complete sleeve around the post and the wire attached to it.

The connection looks good without a magnifying glass and is rigid and so gets by. If a manufacturer tests the part and it actually does conduct for a while when maybe in like a test fixture it would conduct, later it may be an intermittent that eventually goes to an open when in the final product.

I know from some Honda products that I got they are sold after a put into service in front of the customer. These kits I might think possibly that the motor as a whole is not tested, but rather as separate parts. It is not really quite the same thing to knowing what you get runs.

The other case where a non-connection (insulation) is needed to be, is where inside the windings the magnet wire insulation coating does not rub off between two adjacent wires causing a short.

I have seen a similar kind of failure where a manufacturer had mounted the old style through metal film resistor next to an adjacent one of the same. The problem was that the wattage rating of the resistor was not available so the parts they use where of a higher wattage rating just to get by temporarily.

This would have been OK, except that the space on the board had the two adjacent resistors rub the thin outer coating off and they shorted. Maybe if a coil magnet wire is wrapped to tight the same situation essentially happens.

MT

I have had 3 magnetos fail, all due to moisture. When I first got this engine, the gasket that came with it did not fit correctly. I took a round trip of approximately 40 miles one day, the return leg of which it rained profusely during. The next day, I got about a quarter of a mile down the road, maybe a 1/2 mile, and the engine suddenly died. I ran without a magneto cover gasket for awhile, and replaced the magneto. The next time the bike got wet, the mag failed again. I put some red rtv around the magneto cover, and that sealed out moisture for awhile. However, at some point the rtv began to peel away, most likely due to spilling gas on that side of the engine when disconnecting my fuel line for one reason or another. One day it rained again, and the next day the bike would not start. I did some troubleshooting because I was hoping it was not the mag, but nothing else I did was helping. Finally, I broke down and removed the magneto cover. Water came dripping out, and the paper/cloth or whatever that covers the windings had gone from its usual white to a tell-tale rusty brown. I had a spare mag, so I swapped it out. I remembered someone recommending using silicone spray on exhaust wrap to seal out moisture and prevent rust between the wrap and the pipe, so I thought maybe this silicone spray is good for waterproofing, and I just so happened to have some. I shot the mag up profusely with the stuff before installing it. I also had a new magneto gasket which fit better. However, the next time I went to remove the mag cover, it had rained in between then and the time I had replaced the mag. When I removed the cover to install a generator to run my headlight, water again dripped out. I decided to take the bike around the corner to see if it would start, and lo and behold, it did! The silicone spray saved my mag. What I discovered about the magneto cover gasket I had was that it was a paper/cloth material, and water absorpent. When it could no longer absorb water, it allowed the excess into the magneto compartment. Even though the silicone spray had protected my windings, I still did not want water in my magneto compartment. I first considered spraying the gasket with silicone spray, but I did not have much left, and was not sure I would have enough to coat the entire gasket thoroughly. What I did have, however, was almost an entire can of spraypaint that I did not use because it was the wrong color for what I wanted to paint. Paint is waterproof, so I decided to paint the gasket to make it waterproof. put the gasket on the end of a length of twist wire and coated both sides profusely with paint until it began to drip off the gasket and spatter on the ground. I hung the gasket by the twist wire on a hook outside of my back window and left it outside to dry overnight (it was well after midnight when I did this). I reinstalled it the next day, taking extra care to make sure that all the screws holding the magneto cover were as tight as they could be. I have not opened my mag compartment to check for moisture, but I have not had any issues with starting since. I forgot to mention that when I painted the mag cover gasket, I also shot the mag with more silicone spray as an extra precaution. Long story short, silicone spray on the windings in addition to spraypainting the mag cover gasket were the best precautions I felt I could take, and they seem to have worked out well for me so far.

I'm not sure what moisture does to cause a mag to fail, but have seen it several times. I suspect that it is a mechanical failure due to vibration causing the windings to rub together and short out within the coil. My guess is that the water loosens the binding material that wraps the coils tight around the core.

I've got an old coil-winding machine here from the 50s, but as cheap as these are I haven't even unwound one to look for the cause.

crassius said:

I'm not sure what moisture does to cause a mag to fail, but have seen it several times. I suspect that it is a mechanical failure due to vibration causing the windings to rub together and short out within the coil. My guess is that the water loosens the binding material that wraps the coils tight around the core.

I've got an old coil-winding machine here from the 50s, but as cheap as these are I haven't even unwound one to look for the cause.

Click to expand...

copper corrodes, corrosion increases resistance, also, moisture conducts current, which will short out a mag.

That actually makes a lot of sense, mooner. I never thought much about it, but that explanation is very logical.

the coil windings are coated with enamel for their entire length except for the very ends - I doubt any corrosion would occur within the coil

crassius said:

the coil windings are coated with enamel for their entire length except for the very ends - I doubt any corrosion would occur within the coil

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They come from china, and given how cheap they are and the quality of some of the other parts in these kits, do you REALLY think those windings are properly protected? And if they are, why do so many of them fail? Think about it, bro.

have you seen the quality? i know the wires are insultated, but tell that to the few who got junk mags from the factory that never worked once. also, if there is any cracks in the coating moisture will find it.

but that moisture would need to find two cracks in two places to short out that area

my bet is on friction caused by water loosening the mounting wrap wearing between two wires and getting a short right there, right now

no biggie really as these are too cheap to try to do anything about it

I dont know. When my one mag went out, it was fine the last time I drove it before it rained, wasn't driven during the rain at all, and when I went to start it after it stopped raining, the magneto was shot. It was still wet when I tried to start it, but it didn't fire once. Corrosion can definitely short a connection. I have seen things that run on batteries not work due to corrosion on the terminals. If the corrosion can be sufficiently removed, the device will work again. Perhaps corrosion occurs somewhere in the windings somehow, even though they are insulated, and thats what stops a wet mag from working. Perhaps there is some place on the windings where moisture can seep in and corrosion occurs very quickly.

what friction, there is no contact with any moving parts in the mag,and it would not need 2 cracks, one crack and the exposed soldered end is all it takes. i have had a mag fail 3 times in 3 seperate rain storms and each time i threw it in the over at 250 for 2 hours to dry out, worked fine after that, after the third time it toasted for good

Hey measure twicw,

What I meant by the comment " that I check the soldered point" is that if I encounter an electrical issue, I just go back to all the soldered point I have done previously (which I knew were good when done) just to make sure that vibrations from me riding hasn't caused any of therm to be compromised. I was a certified welder back in the 80's and a Senior Systems computer engineer since the 90's, so I agree wiy
th everything you wrote, I have seen many weld and soldered joints that looked pretty on the outside but had no bonding or strength after testing and x-rays. It was good you pointed it out, maybe someone will go back and redo a soldered connection they had done, which looked good, but actually was providing no connectivity and they thought they had a failed part.

Ron

I've seen vibration loosen these to the point that the whole winding slid up & down on the core. If these were worth the effort to rewind, I think I'd file the sharp edges of the core smooth and also set a pin thru to stabilize the winding. A better design would have put the winding horizontal at the top or bottom, rather than vertical at the side.