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S20's
Continental/Bendix S20's. The lightweight propped Cirrus's are seeing too many mag gear failures. Specifically the ones with lightweight props (Hartzel or MT composite - the MT is STC'ed the Hartzel is stock) and lightweight starters (ST-3 for example). Usually it is only one mag but I have helped replace a dual mag failure (not an in flight failure) before.
I don't think we have seen or heard the last of this. Quote:
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More info
I am flying with a sensi ground adjustable prop. Do you have any info about these mag failures. How does he know it had anything to do with the prop? What failed in the mags. Same problem all three times. Would like to hear about this
Cm |
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Locking tool
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Mags
I wonder if those mags were current on the 500 hour inspection??
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Mags do fail for other reasons. 30 years ago, rented 172, landed at an airport with the same FBO. Plane wouldn't answer mag check, and I was told to, "Fly it home." I refused, took a 182 back, and they tried to fly the 172 the 20 miles, only to have the other mag fail on the way. No damage, thankfully. I had a single failure on my 9A. BTW, no failures so far on my E-Mags.
My guess on those failures was too many hours, too little service. Bob |
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Best, |
Slick Mags..
BTW my Cherokee 180 has "cushion blocks" on the mag. Also, when I overhauled the engine at 2460hrs it had gone through 6 mag failures in about
15 years, all Slicks. I think the cushions do help, but the failures were a great deal more than Bendix mags I've flown. John |
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Could you get me a link or pointer to this service letter? Thanks. Johan |
Possibly we should stop confusing Bendix and Slick type mags, they are significantly different designs.
Bendix mags use a red mark on one tooth of the nylon / composite distributor gear, which when lined up in the witness hole, is the #1 firing position. The SB concerning the use of a lock tool only applies to Bendix type mags. I have an old type brass lock tool that screwed into the witness hole. The issue with it was that when you screwed it in, it was possible for the gear teeth to get damaged if the lock tool teeth didn't line up properly. Slick mags use a pin inserted through the back of the distributor which aligns the gear in the #1 firing position and the is no way to damage the gear teeth with the alignment tool pin. (unless you jam it in or turn the mag with it installed) Use of "non-flexible" gear lock tools has been covered by the SB for a very long time. Most current looks are now made of flexible material that do not screw in (press in) and should not damage the gear teeth. In practice, you really don't need the lock tool, unless you bump the main drive gear out of position during installation of the mag to the engine. TCM IO-550s (6 cylinder mags) use a two eared male drive couplings instead of gears, which fit into the female coupling with rubber dampers. The rubber dampers are supposed to reduce shock loads from the engine drive to the magneto. It is not that uncommon for the nylon distributor gears in the magneto to get shock damage from the engine drive due to starter kick back or impulses from the engine. Vacuum pumps sometimes suffer the same fate. I spoke with a Slick mag engineer once about using nylon / composite distributor gears and I was told that it has to be a non conducting material, so nylon seems to work the best. That is why there is a 500 hr inspection, to inspect the gears and points etc. The failure at 200 plus hours might be attributed to a starter kick back issue or even excessive RPM excursions or possibly faulty drive gears. I had one fail in less that 20 hrs on a Baron after a 500 hr insp due to installation error. |
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