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Magneto overhaul necessary?

What mag type and what engine type was it?

It is possible for Champion spark plugs, the ones with the defective resistors, to destroy a magneto, by internal flashover taking place for hours.

It seems the Bendix mags are OK but other makes are not as robust.

I use Tempest fine wire plugs now, having seen a nearly 100% resistor failure rate on all my Champion plugs going back to 2003.

Administrator
Shoreham EGKA, United Kingdom

Not sure about mag type, but engine is Lycoming IO-360. That was something with mechanical part of magnetos, with gears as I remember…

EVCA

They would AFAIK been Bendix mags. Can they be Slicks? Slicks are “throw-away” mags.

My guess is that your mags were rebuilt by a monkey. It does happen.

Administrator
Shoreham EGKA, United Kingdom

It concerns a four-year life limit which has been at times incorrectly interpreted.

It does depend on some factors, suchs as your maintenance program, kind of operation and regulatory body your under. Under EASA AOC you would be required to follow this limit. For private fliers it depends on how the state or registration decided, their is not a single YES/NO for this for aircraft under EASA regulations. The linked document is valid, but only for N flyers. I don’t see any benefit from overhual, but do see for inspection.

How does a Magneto typically fail?

It does depend on which type of magneto. In general they contain mechanical parts, such as coupling, bearings, contact points, which require proper lubrication. This is a problem on some engines, suchs a Continental engines with the magneto’s on the top side of the engine / facing forward. These don’t get lubricated as other design, so are when left installed for long times weak points.
Contact points on all “modern” magneto’s will wear out in out about 500-1000 hours. It does make sense to have these replaced every 500 hrs.

On bendix magneto’s the plastic gear tend to loose teeth occasionally, which is something you don’t want. On Slick magneto’s that doesn’t happen, but the distributor electrode can get loose, firing to a random cilinder if left uncorrected. Condensators are often overlooked, especially on D2000/D3000 magneto’s, as these often stay with the aircraft. Bad condensators will wear out contact assy very fast, and can cause rough running. With single Bendix and Slick magneto’s these are to be tested every 500 hours.

The coil can fail at random. Sometimes a broken coil will still work, so it is good to get a 500 hours inspection done, to detect this early. Sometimes the coil is dead without any announcement. A D2000/D3000 has two coils, so it would only affect one of two magneto’s.

I don’t know what ‘mandatory’ means in relation to impulse coupling spring replacement, as there is no AD on them that I’m aware of.

It is mandatory according the magneto service manual. It might be different on N and EASA how these are looked at.

It seems the Bendix mags are OK but other makes are not as robust.

I don’t agree on this. In the past (say 20 years ago) Slick produced poor quality magneto’s. I think the design of both magneto’s is quite good now. On quality I would say they are equally well, or Slick a little better. The craftsmanship at the factory is much better at Slick then at Bendix / TCM. Some assemblers at Bendix/TCM really doesn’t seem to know how to assemble one / poor QA.

It is possible for Champion spark plugs, the ones with the defective resistors, to destroy a magneto, by internal flashover taking place for hours.

In my experiance it is very rare that it does damage bendix mags with newer brown distributor block. The older black blocks seem to be more senstive to this internal flashover fire issue. Offcourse, the flashover happens somewhere else then. So change of damage on your ignition leads.

JP-Avionics
EHMZ

Slicks are “throw-away” mags.

Not true! They are good mags as well. They do need maintenance, just like others.

My guess is that your mags were rebuilt by a monkey. It does happen.

Based on the discription it sounds how I have seen many factory bendix single magneto’s. Sometimes they do have a lot of play. On helicopters factory rebuilts do tend to fail before reaching 500 hrs. The additional vibration will ruin the complete inside if it has play on the bearings.

Due to the difference in construction between Bendix dual and single magneto you won’t see that on dual magneto, as the axle support is designed completely different to a signle one.

Slick magnetos also have a different much more simple axle support, which is less likely to develop that kind of damage. Though even on a single bendix this doesn’t need to happen, if it is assembled correctly.

Last Edited by Jesse at 27 Apr 15:55
JP-Avionics
EHMZ

To clarify: I would never factory rebuild mags. I send them to a specialist overhaul shop (USA).

If I bought a new Lyco engine I would not fly it. I too would first send it to a specialist engine shop (Barretts, Tulsa), to make sure all the screws are done up, etc

Most people I know who use Slicks say they throw them away when OH time comes (500hrs or whatever).

The capacitors (condensers) get changed at magneto change on mine. The OH firm sends two new ones. Curiously they don’t look new at all; they look very old. Perhaps they are re-using old casings?

Last Edited by Peter at 27 Apr 16:57
Administrator
Shoreham EGKA, United Kingdom

Most people I know who use Slicks say they throw them away when OH time comes (500hrs or whatever).

Slick magneto’s have a 500 hrs inspection interval. (or 250 hrs for single magneto installation suchs a motorgliders) Overhaul limits are equil to engine limits. Overhaul of Slick magneto is more expensive then new magneto’s, and their quality is quite ok from factory, so I just doesn’t make sense to overhaul these.

The capacitors (condensers) get changed at magneto change on mine. The OH firm sends two new ones. Curiously they don’t look new at all; they look very old. Perhaps they are re-using old casings?

That is very sensible. This is often overlooked by many shops and aircraft owners. They are a bit of dull finish, so the might look a bit old.

JP-Avionics
EHMZ

I am just a bit pi$$ed off. Had my magnets overhauled, because my examiner told me to do so. They worked perfectly fine and had run 200 hours (but had more than 4 years).

So I plopped them off the engine, sent them to the overhaul shop and am presented a bill of more than 2.5k. What was that?

What the heck is happening here? I haven’t dropped another clanger so far, but this one definitely was a big kick in the … wallet.

It was beyond my imagination that it could cost so much, else I would have contacted other shops before. First Quote on phone was 700 if all was fine so I just said just do it.

I’ll definitely go for minimum programme as soon as possible 😬😬

Germany

What I do in the Cirrus SR22 is after 5 years, I get an inspection done, then run them another 5 years. After that, I replace them with overhauled exchange ones (largely the same cost as overhauling yours, and no downtime). Then the same again. This has been the perfect solution in 17 years so far. Of couse, I am N-reg. Part 91, so no maintenance program BS, and no „mechanics“ telling me what to do, etc.

Last Edited by boscomantico at 11 Oct 19:32
Mainz (EDFZ) & Egelsbach (EDFE), Germany

Sorry to hear that. Now you know how to handle it next time. Disregard the calendar time and fly it to 500 hrs or so before any action if they perform well.

For this money you could have (almost) gotten an electronic one.

ESSZ, Sweden
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