Overthinking dual magneto? - aircraft purchase

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Squall
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Overthinking dual magneto? - aircraft purchase

Post by Squall »

Hello all,

New to the board but long time reader. I am getting close to seeing aircraft ownership as a possibility. I am looking for a M7-235B and was sold on the B4B5 due to mogas STC possibility with the state of 100LL. There are two IO-540 W1A5 equipped planes that I like everything else about. I see the pros of injection and will likely be operating with fields with 100LL anyway, but is the dual drive magneto worth worrying about? I have read everything I can find and don't see reliability as a concern with proper 500 hour inspections, but wanted to see what the current state of parts availability was from user experience. It looks like Kelly Aerospace is manufacturing parts. It also looks like a certified electronic ignition/ single mag retrofit is still a ways off. I appreciate any insight!

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Post by Kirk »

Comes down to personal preference. The single drive dual magneto goes against what seems like common sense. I’ve been operating my M5 with the O540J1A5D for 14 years.

I was initially concerned but talked with some engine shops and all told me that they had not seen any higher failure rate. One pointed out that a drive failure within the case would trash all the accessories any way so in that scenario, separate mags would both fail anyway.

You are correct that any electronic ignition is a long ways off. Been hearing “next yearâ€￾ for 14 years on that issue.

Parts haven’t been a problem. Kelly Aerospace has stepped up.

I would prefer separate mags but sure wouldn’t turn down a really good airplane over that one issue.

So there you go, just one guys opinion. You will find many others.

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Post by captnkirk »

Funny I spoke to Electroair at OSH . They have gone to a dual cdi style set up as opposed to one mag and one electronic ignition. The 4 cal should be available late this year and they said the 6 cyl would be in 2019. We have heard that before but they said the feds where working with them a little better. Hopefully it will come about ,the fuel savings could justify the expense for a lot of us.
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maules.com
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Post by maules.com »

Squall, if the O540 B4B5 engined M7 doesn't already have the autogas kit and STC already fitted, it will cost well over $3500 by the time its fitted.
Most times you fill up you load 50 gals. Very few airports now have mogas and when you go out of your way to get it you have to test for ethanol content, so its not always the best choice, plus your engine will use an extra 1.5 gph over the IO540 W1A5 or W1A5D.
just some thoughts, though if the perfect Maule is in your sights don't shy away because its B4B5. I have a W1A5 I can give you the numbers on. pm or call me
Jeremy
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Post by StuporRocket »

I just sold my 1990 M-7-235 with the IO540-W1A5D (& I HATE myself for it). I had the same concerns about the single drive dual mag and talked to a buddy with a mag shop in ATL area. He gave the same advice as above & did my 500 hr service on them. With 2000TT on the original mags (always properly serviced) I never had any trouble & the airplane had no trouble prior to my ownership. I wouldn't hesitate again at all.
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andy
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Post by andy »

Mike Busch does a good presentation on mags at https://www.youtube.com/watch?v=cOr3b10zmrQ.

At 46:12 minutes into the presentation, he talks about Bendix single and dual mags and Slick mags. He's not a fan of the dual Bendix mag since not all of the parts are available anymore. Continental owns Bendix and only manufactured the dual mag for Lycoming engines (hmmmm). They decided to stop supporting the dual mag, which is why not all parts are available for it anymore. Mike is also not a fan of Slick mags and feels that they are not as durable as Bendix mags. At any rate, it's a good presentation.
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andy
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Post by andy »

The biggest consideration with a dual drive magneto is that the bearings and gear drive are single points of failure vs. two magnetos. I haven't seen the parts breakout for it but I think there's two of everything else inside the case.

The ideal arrangement would be electronic ignition, of course. Getting ride of mechanical points and a rotating distributor with air gaps eliminates many of the problems associated with older technology. Solid state circuitry is far from foolproof but years of use in the automotive industry have proven the reliability of electronic ignition.

However, electronic ignition requires an electrical power source to operate. The big benefit of magnetos is that they continue to operate (along with the engine) even when the aircraft's electrical system fails since they are mechanically driven off the engine.
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StuporRocket
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Post by StuporRocket »

Most electronic ignitions come with their own backup battery supply which is also kept charged by the onboard electrical system and monitored independently of the aircraft system.
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Post by VA Maule »

E-mag P model
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Squall
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Post by Squall »

Thanks for the replies - it definitely helps to get first hand experience. Jeremy - I emailed you a week or so back on 555. That is looking like a good fit and the other plane we were watching went under contract. I'll give you a call when I get more sure.

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Post by Squall »

Last question: Is the IO-540 V4A5 260 hp model independant or dual magneto? SL#70 leads me to believe that it is independent but I couldn't find anything searching the forum. Also going by the Service Letter, it looks like there are some IO 235 hp models with certain SNs that have independent mag. Any year guideline or has anyone come across this?

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maules.com
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Post by maules.com »

The only 540 engines used were the O540 J1A5D and IO540 W1A5D which was later changed for W1A5.
The letter D lets you know if it’s a Dualmag. No D and it is a separate mags engine.
I’m not sure if the date change but approximately the end of the ‘80s however at overhaul some engines had the accessory changed from D engine to separatemag engine
The D engines are lighter weight and since Maules first use of the engines at end of 1975 ihavenever had one fail on me
Jeremy
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Squall
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Post by Squall »

Jeremy- Is the 99 you have listed a W1A5 (no D)? If so I may have been misguided if the J/W series D engines were earlier production models. I got it in my head that all of the IO-540s were dual... until seeing SL#70. I understand the the dual is not a deal breaker either but it is a consideration on the serviceability front.

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Post by maules.com »

Correct, no D on a ‘99. Roughly no D since about ‘89 But in case an engine has been changed one should check each airplane ‘in case’ if it’s important.
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Post by StuporRocket »

My November 1990 M-7-235 had (has) the W1A5D. I believe it is SN: 4092C.
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