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Thread: Magneto 500 Hour Inspection

  1. #1
    Member stroutmail's Avatar
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    Default Magneto 500 Hour Inspection

    Thoughts on this. Send it out for overhaul? Buy new?
    S4LN-21 or S4LSC-21 Bendix? Change over to Slicks?

    I am running C72AE Senenich Ground Adjustable..450 hours with Bendix mags. Running very well except for small resonant vibration at 1900 RPM.

    Opinions appreciated.
    Last edited by stroutmail; 12-26-2018 at 04:36 PM.

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    Member stroutmail's Avatar
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    Senior Member chipallen's Avatar
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    Default Re: Magneto 500 Hour Inspection

    First, the "always required" disclaimer: The following is simply to relay my personal experience with Bendix magnetos, and my opinions as a result of my own extensive investigation alongside Sensenich and Continental (manufacturer of the Bendix magnetos) prior to the issuance of the Sensenich Notification Bulletin. Any course of action you choose should only be the result of your own investigation and consultation with your maintenance technician.

    I owned a Beech Baron for 30 years, regularly ran engines (Continental IO-520E's with Bendix magnetos) well past TBO, and never, not once in those 30 years (7,000 hours and 6 engines) pulled a magneto (except for annual inspections). IMHO, they are remarkably dependable.

    Having also owned several Sport Cubs, there is a bit of an issue running the Sensenich Ground Adjustable Propeller with Bendix mags. If you haven't already seen it, you might want to review the Sensenich Notification Bulletin attached.

    I discussed this issue extensively with the manufacturers (CubCrafters, Continental, Sensenich) prior to the Sensenich Bulletin in 2013 and as a result of these communications, I believe there are three schools of thought in dealing with this issue. First, change out the mags (we replaced the Bendix mags with Slicks following a mag failure, and because we really liked the Sensenich Ground Adjustable Prop, it seemed to be right course of action). Or, secondly, change the prop; because the issue is related to harmonics, changing the prop to a McCauley aluminum (flywheel effect), is a good move, as well. Price-wise, I believe a new set of Slicks with harnesses or a "like new" McCauley aluminum prop are about the same money.

    The final option is to leave well-enough alone. If the mags are working well, and nothing "scary" is found during the annual condition inspection, run them another year. Small mags like those on the O-200 are not likely to disintegrate or cause any major engine damage, and that's why you have two of them. The two mag failures I have experienced over the years (both of them on Sport Cubs, and both with the Bendix / Sensenich prop combination) have been the result of a broken drive shaft (after which we replaced the mag). Also interesting that there doesn't seem to be any "time frame" where a failed magneto is more likely; if I recall correctly, one of our mag failures occurred at 150 hours total time and the other was at 600 hours. Further, I would venture a guess that of the 90 or so Sport Cubs in the fleet, there are a lot of airplanes still running the Bendix / Sensenich combination with no problems.

    A number of years ago, (early 2013) a Continental factory technician visited my hangar in Atlanta to personally inspect the magnetos (at the time, I was running Bendix magnetos and the Sensenich Ground Adjustable Propeller). Following his inspection, the recommendation was to continue running them, but also to check them carefully at every oil change.

    This all goes into the "for what it's worth" column.
    Attached Files Attached Files
    Chip Allen
    SWT Aviation, Inc.
    Cubcrafters Southeast Sales Center
    Marietta, GA
    www.swtaviation.com

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    Member stroutmail's Avatar
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    Default Re: Magneto 500 Hour Inspection

    Thank you Chip for the excellent feedback. Not having examined the failed parts it is hard to draw conclusions, but premature failure of different drive shafts at variable intervals sounds a lot like a metallurgical QC issue. Resonant frequency (harmonic) related failures should be more universal IMHO--plus a harmonic vibration strong enough to break a drive should be noticeable to the pilot. (SB643C calls for complete replacement/overhaul of certain units before they are five years old! (prior to older than Dl5FA000(R))

    http://www.tcmlink.com/pdf2/SB643C.pdf

    Was the changeover to Slicks an "easy" job-----like "bolt on"? (Same engine drive gear?)
    Did you use impulse drives on both of the new mags, or did you go with "Shower of Sparks" design?

    Will you replace, overhaul or IRAN the Slicks every 500 hours? (I have read the Champion-Slick SB's and it appears they have their own sets of issues.)

    I wonder if anyone changed to a metal or wood prop and still experienced a premature Bendix mag failure? The original wood Senenich W72GK44 like all wood propellers provides some protection (damping character of wood) against harmonic resonance.

    The more I read, the more it seems these devices (TCM-Bendix and Champion-Slick) are "not built like they used to be".

    And, it seems TCM made some sort of improvement in 2015 (after SN "D15xxxxxx)...Latest SB643C changes overhaul replace from 4 years to 12 on new mags.
    Last edited by stroutmail; 12-28-2018 at 06:34 AM.

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    Senior Member chipallen's Avatar
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    Default Re: Magneto 500 Hour Inspection

    Quote Originally Posted by stroutmail View Post
    Thank you Chip for the excellent feedback.

    Was the changeover to Slicks an "easy" job-----like "bolt on"? (Same engine drive gear?)
    Did you use impulse drives on both of the new mags, or did you go with "Shower of Sparks" design?

    Will you replace the Slicks every 500 hours?
    Yes, going from Bendix to Slicks is "super-easy". Pretty much plug & play, but you do have to buy new ignition harnesses with the new mags. Impulse drives are simpler and less expensive (and they are covered in the Continetal O-200 Type Certificate; no sense in reinventing the wheel, so that's the option we took. (I don't recall the SOS system being available on the O-200 mags; we just went with what was already on the engine).

    As mentioned previously, I think the Slick magnetos are extremely dependable and I prefer to take the IRAN route with a really good inspection at every annual.
    Chip Allen
    SWT Aviation, Inc.
    Cubcrafters Southeast Sales Center
    Marietta, GA
    www.swtaviation.com

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    Member stroutmail's Avatar
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    Default Re: Magneto 500 Hour Inspection

    Certainly seems that extra care and caution is merited here---even for those that have not yet experienced issues. I am approaching the 500 hours---no problems to date with the Bendix mags and Sensenich Composite Prop. Since it appears that the issue may be more than just vibration, but also metallurgy--I am a bit reluctant to IRAN or even rebuild my mags without changing major components--at which point the price of new seems (relatively) attractive. Add this to TCM's SB643C calling for replacement/overhaul of mags more than 5 years old:

    "3. Magnetos with serial number older than Dl5FA000(R)1, El5FA000(R)1, or Fl5FA000(R)1(June 1, 2015) must be overhauled or replaced at the expiration of five years since the date oforiginal manufacture or last overhaul, or four years since the magneto was placed in service,whichever occurs first, without regard to operating hours. Also at this interval, CMI (formerlyBendix/TCM) high tension ignition harnesses with serial numbers K15E or older must bediscarded and replaced.4. In addition to the requirements listed above (Section D., steps 1. and 2.) S-20, S-200 and S1200 series magnetos with a serial number newer than Dl5FA000(R)1, El5FA000(R)1, orFl5FA000(R)1 (June 1, 2015) must be overhauled or replaced at the expiration of thirteenyears since the date of original manufacture or last overhaul, or twelve years since themagneto was placed in service, whichever occurs first, without regard to operating hours.Also at this interval, CMI high tension ignition harnesses with serial numbers Kl5F or newermust be discarded and replaced."

    Horror stories about mag failures...

    https://www.pilotsofamerica.com/comm...estruct.54654/

    Back in 2012, Adam Sloon (Cubcrafters) wrote: "Continental, on their own, have inspected customer aircraft and determined the magnetos to be in good shape and offer that the first sign of a problem is fretting on the drive gears."

    Fretting is caused by vibration and/or issued related to surface hardness.

    So, I am wondering if in addition to replacement of the mags, would it be prudent to replace the drive gears SA36066????? They are very expensive though--like $600-700 each. Maybe a visual inspection and a magnaflux would be enough. (Read the link above about the broken drive gear--two teeth broke off--of a Slick mag at 1000 hours.)

    The "Kit" for two 4301 Slick mags, harness and plugs is around (K4520-40) $2700. The "Kit" for two new Bendix mags and new harness (10-400452) is around $3200.

    Ignoring the 12 year TBO on a low hours engine seems prudent, given oil analysis, compression leak testing, and bore-scope inspections, but figuring out when a drive gear or shaft in a mag is going to break seems less transparent. So, replacement of "questionable" mags at 12 years seems wise. And replacement of mags at 500 hours might be wise for those who fly with "an abundance of caution".

    Any other opinions?




    Last edited by stroutmail; 12-28-2018 at 10:44 AM.

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    Senior Member chipallen's Avatar
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    Default Re: Magneto 500 Hour Inspection

    Quote Originally Posted by stroutmail View Post
    Back in 2012, Adam Sloon (Cubcrafters) wrote: "Continental, on their own, have inspected customer aircraft and determined the magnetos to be in good shape and offer that the first sign of a problem is fretting on the drive gears."

    The visit by Continental to my hangar prior to the Sensenich Bulletin was precisely as you (and Adam Sloon) quote; the technician pulled both mags and "inspected" them along with the drive gears, under magnification and very bright light to determine condition. I'm not expert, but I assume the guy that Continental sent to Atlanta was.

    No doubt that your investigation into this is making all of us smarter!! Thank you for your effort and for taking time to post.
    Chip Allen
    SWT Aviation, Inc.
    Cubcrafters Southeast Sales Center
    Marietta, GA
    www.swtaviation.com

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    Member stroutmail's Avatar
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    Default Re: Magneto 500 Hour Inspection

    It is difficult to judge "what is best product" these days. Careful reading of opinions and anecdotes of Slick vs Bendix seems very much like the Ford vs Chevy discussion.

    Also, corporate and management change over the years has been quite profound. And, all the while, we have traveled thru a change in values regarding reliability, engineering safety factors, outsourcing of suppliers. quality control. and demands for growing profitability.

    Read "Google" the history of Unison, TCM, Transdigm. Slick Electro is bought in a leveraged buyout by a Harvard MBA. Unison sold to GE, then to Transdigm, aka Champion Aerospace. Bendix goes to Continental which gets taken over by Chinese. Oh my. The decision by one new purchasing manager to change suppliers of one component can change the reliability alot. Moving production from one facility to another can also introduce changes in quality.

    Kind of makes the anecdotes, "I ran my 1960 Bendix mags over 4000 hours" less relevant. A modern telephone with an ATT logo is nothing like that bulletproof Western Electric one my family used in 1970. Maytag and Amana appliances are not what they used to be.

    Probably need to make decisions based on experience with recent designs and production.

    Recent info seems to favor Champion Aerospace (Transdigm) "Slick". Their support videos and literature seem to signal a positive/superior program.
    Last edited by stroutmail; 12-29-2018 at 06:04 AM.

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    Default Re: Magneto 500 Hour Inspection

    Chip's advice earlier, "Any course of action you choose should only be the result of your own investigation and consultation with your maintenance technician." is very wise. For "what it's worth", I will share the "result of my investigation" and my decision, just in case someone else is pondering the same issue.

    First, sound decisions are almost always based on inadequate information and probabilities of less than 100%. That said..facts..

    1. My observation (other people's experience) is that mags (Bendix and Slick) have a high probability of requiring significant maintenance over a 500 hour run. Seems prudent to remove/disassemble them for a serious and careful visual inspection at 500 hours--maybe even more often. This inspection should probably include drive gears.

    2. All rotating machinery is subject to "harmonic resonance". Every rotating machine and component has a "critical" speed or "resonant frequency" where stress increases to a level significantly higher than desired for long life. Most machines are designed to be operated "under-critical" or at a speed (RPM) below "critical". In the early days of aviation, it was the engine crankshafts that failed! (Read about the Graf Zeppelin that lost four of their five engines due to harmonic resonance. As a nerdy engineer, I find technical articles to be interesting--in the past few weeks I have spent considerable time reading the literature regarding torsional vibration.) Critical RPM is increased by a reduction in mass or an increase in stiffness. So, a mag with less inertial mass will have a higher critical RPM for "resonance".

    Conclusion: The Bendix mags are heavier with more inertial mass and probably less damping. Changing to the lighter Slick mags probably increases the "critical" RPM of the mags to a level outside normal operating range and maybe even less stress overall from torsional vibration. The Sensenich
    2EK/C72AE composite prop probably changed the torsional vibration input to the mag drive to match the "critical" or resonant frequency of the Bendix mags at certain RPM's. Relatively continuous periods of "cruise" operation at this critical RPM where stress was above normal led to premature failure of the mag drive---with some drives failing earlier due to metallurgy or machining at the low end, or outside of the spec. (Important to consider that Continental's Recommended Max Cruise RPM for a 200-A is 2500 RPM.) The only indication of potential failure or "early warning" would be thru a visual inspection of the drive gears looking for fretting or an actual crack in a drive gear or shaft. Bendix mags with drives at the higher (stronger) range of metallurgical and machining tolerances and or planes operated at "under-critical" or seldom at critical speed have survived--so far--and a certain population have a probability of a very long life--especially if operated at lower RPM. (Redline RPM on these little engines over the years may be as much related to harmonics and critical resonance as it is to valve train and connecting rod life.) My plane has been operated since 2009 with the 52 cartridge, so it has been running at a lower RPM..climb performance is good..with a 48 it must be truly amazing.

    3. TCM's SB643C (July 2017) with the recommendation to overhaui or replace pre-2015 Bendix mags after five years sends a signal that there is a higher than acceptable (to me) failure risk of a certain group of their mags. These recommendations are almost always a compromise joint decision of engineering, marketing, and legal. One should always remember that although "recommendations" may not carry a legal obligation for the pilot to comply--a manufacturer essentially creates a legal defense and avoidance of liability in the pilot's "failure to comply with recommendations".

    4. The nature of a mag drive failure is different from an electrical failure. A broken drive gear tooth can damage the crank cluster gear and lead to complete engine failure--having a second functioning mag might not be any benefit. Yikes! While I practice engine off, dead stick landings and try always try to be prepared---I hope that I never have to actually experience a complete engine loss of power.

    5. Other pilots have had good experience continuing use of the Sensenich composite prop after changing to Slick mags--even when running the 48 cartridge with higher RPM's.

    Decision: A) Remove and replace my 2007 Bendix mags at 475-500 hours (this year's annual). Even if no signs of drive gear fretting are evident, the probability of possible failure is too high for me. The reduction of risk is worth the $ cost--to me. B) Carefully examine drive gears (visually and magnaflux or other crack checking). C) Replace the mags with new Slick mags--new harness and new plugs. (I considered buying new post 2015 Bendix mags---but though I guess they are "stronger" than the "questionable" batch, they are still heavier and likely have a very similar critical speed issue. I think the probability is high that the Slick mags are "under-critical" if engine RPM is maintained below 2700, meaning I can use the awesome for climb 48 cartridge with the Sensenich propeller. (I will still "cruise" in the 2200 to 2400 RPM range.)

    Note: IMHO, It may very well be that Bendix mags "in general" are more "robust" than Slick mags in most applications (Just generally heavier and more "meaty"--but in the unique case of the
    2EK/C72AE prop in a low and slow plane like the CC11-100 running a 0-200-A, they are not the ideal. BTW, CubCrafters has confirmed that an MRA is NOT required to replace the Bendix mags with the appropriate Slick mags..

    Last edited by stroutmail; 01-08-2019 at 05:37 PM.

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    Default Re: Magneto 500 Hour Inspection

    Another insight, Chief of Technology at Champion Aerospace, Joe Logie recommends that we run REM37BY plugs in the 0-200 A. They can be ordered with the kit of two mags, wires and plugs..although probably not in stock at distributors. (Kits may not be in stock but the components are and not much price discount in the kit.) The REM37BY resist lead fouling and present the spark further inside combustion chamber for better starting and fewer misfires. They are listed in latest Champion Product Catalog as applicable to 0-200 A.
    Last edited by stroutmail; 01-08-2019 at 07:55 AM.

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