OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk Ignition coil delaminating

Hello all...

I have another Briggs & Stratton 375 that I haven't spent much time on yet (because the base is cracked like you wouldn't believe so is falling to pieces). But I have started it, so it runs.

I noticed the coil is rusty and delaminating at one end. Its laminations are fanning/spreading out away from each other due to the rust.

Since it's still producing enough spark to run (and a new coil costs around $60-$90, it's not worth replacing. But is there a backyard fix to halt delamination of the coil? Like grinding the rust off with a wire brush in a drill - then painting with nail polish, or something similar?

Also, because it's fanning out - if I grind the rust off as best I can - I wouldn't then be able to compress the laminations with spring locking pliers, would I? (Because if it's the same as transformers in electronics, I think they coat the metal plates with some kind of insulating paint, then glue them together. Then they wind wire around that laminated core. So if I grind out the rust, then try and compress the plates, I'll be ruining the induction function of the coil, correct - because the laminations will now be touching?)

What about grinding that end of the coil on a bench grinder, or filing it down so the fanning is not as pronounced... I know I couldn't do this much, because that end would be shorter and therefore not close to the magneto anymore...

Suggestions/thoughts please?

Hi justallan, your coil sounds like it has just about reached the end of it's serviceable life, and should be replaced. With a bit of luck, one of our members on this forum may have a serviceable second-hand coil, that may get you out of trouble... Just put your request in the "Items Wanted" thread.

Rust occupies a greater volume than the steel it used to be, so when things rust they expand. (If it happens to reinforcing rods in concrete the expansion of the rods causes the surrounding concrete to burst, which is why they call it 'concrete cancer'.) Your coil has delaminated because rust formed in between the laminations, requiring space in between, which forced the laminations apart. It means water got into the coil and stayed there for a long time. I don't think you can really fix it without ruining the insulation. Rust converter would reduce the volume occupied by the rust by turning it into FeO instead of Fe3O4, but rust converter is extremely unfriendly to insulation.
The problem you have is that rust is hygroscopic: it absorbs water from the atmosphere and continues to rust. You might get some relief by warming your coil enough to dry it out without destroying the insulation - maybe about 80-90 degrees C - for an hour, then sealing it with suitable paint or epoxy. If you keep water out, it shouldn't get any worse for a while - maybe years. However I'm just guessing with that temperature - I don't know what they've used for insulation in various parts of the coil. Replacing the coil and keeping the next one dry is the real solution.
Grinding the rust off the outside of the coil is irrelevant to the problem: the problem is the rust in between the laminations. Yes, removing the varnish from the laminations would cause them to short-circuit each other and increase the hysteresis losses, but that is irrelevant too: the only insulation that matters is in between the laminations, and you can't remove that anyway.
If you can dry the coil out and encapsulate it, it shouldn't rust any more, in theory. Encapsulating it without drying it out will just end up causing your potting material to burst.

There is a ignition coil on eBayat the moment, almost new real cheap.

Link

Grumpy: I was hoping the wire brush on my bench grinder might be able to get most of it out (by whipping between the laminations). But thanks, I do take your point.

And thanks to deejay and Joe... It's had a pretty hard life, the alloy base is smashed into several pieces. So might not be worth another coil. Have to take another look before going that route.

hi all,
ill send a used but working coil if you pay for package and postage, as i have a plentiful supply of them for now. the only thing would be how to pay for postage???
regards jay

justallan, I've tried similar things in the past and the tips of the wire brush strands pushed some of the dirt and rust deeper in. This delaminated a larger proportion of the core: not a good outcome. Posting a few bucks to jay sounds more practical to me. However I must admit that long ago when I was young I used to spend many hours on doomed attempts to 'fix' broken car parts. Some of them worked for a while, but overall my record of success was woeful, and I usually fixed each two-dollar part several times before I weakened and bought a slightly better one from a wrecker. If somebody offered me the chance to be young again, I'd fall down laughing.

Hey grumpy, Amen to that!!

Yes Darryl, the worst thing about being old is the awful experiences you had to go through to achieve it.

Yeah grumpy, you're only here for a short time, but you've got to enjoy the ride!!

Hi Jay... Sorry for the delay. I wanted to check it didn't have anything else wrong first, before wasting your time - and I only got to do that today.

Your kind offer is appreciated. Taken to PM/email.