Replace magnetos on over tbo engine?

[lukejb]

I have the Bendix Dual Magneto on my 77 201J. I have never had any issues and was wondering what is recommended for these. I can see from the logs that the mag has been visually inspected every year at annual inspection in compliance with AD 76--07-12R1 but it appears that it has been about 514 hours since the mag was last pulled and sent off for repair.

Question is with no indications of any mag issues should i send this off for repair at my upcoming annual? If so what does this service usually run on price or is there a range to expect dependent on what is needed?

I have heard that these mags have been phased out and that parts, repair and replacement may be hard to come by in the future. Is there any truth to that? I have also heard that these mags are junk and they really do not give you redundancy and safety of having two separate mags. Have several of these been phased out and replaced with two separate mags?

[jetdriven]

You have two options wih the dual mag. A 1200$ 500hr inspection or 9 grand to convert it to two separate mags.

I am of the common opinion that a properly conforming D-2000 or d-3000 mag from a shop that knows these mags very well is just as safe as two separate mags. After all, they all run from one crank gear and sometimes that fails. It happened to a friend of mine at night, 900 hours since major overhaul.

[lukejb]

Good to know. Think i will stick to the 500 hour inspection. I am in the Dallas/Fort Worth area. Any reputable shops around here that you know of?

[KSMooniac]

Aaron in Lancaster at Select Aircraft is your best bet for the mag work.

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[BigTex]

Aaron in Lancaster at Select Aircraft is your best bet for the mag work.

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I've used Aaron twice and can't recommend anyone higher.  He's also just down the street from you.  Stop by or give him a call.

[lukejb]

Thanks Scott!

[DonMuncy]

+1 for Aaron. A nice guy, knows his stuff, honest and fair.

[cliffy]

It's not the mag that's bad, it's the people who work on them. I ran duals on a Navajo years ago for 1800 hrs with no problems. Did 500 hr insps on them never had a mag problem. Make sure anytime the mag hold down nuts are loosened that NEW lock washers go on before retightening. NEVER just loosen the nuts, adjust the timing and retighten. Always loosen and remove nuts one at a time, install a new lock washer and nut and then do the other one. Once tightened, if you have to loosen again, get another lock washer. 

This actually goes for any mag not just duals. I do it on my O-360 also. 

I've known people who retime their mags for several years and never replace the lock washers. Had a 172 in the shop a while back with one mag actually falling off the engine because the hold down nuts had vibrated loose. 

[AESpecialists]

Bendix and Slick both recommend 500hr inspections. Should be roughly $350 each on average. Cheap insurance, along with checking/replacing the harness and plugs.

 

The Dual Bendix mag is more expensive proposition. Bendix is part of Continental and they saw no interest in supporting a magneto only used by Lycoming. They stopped making OEM parts about two years ago, and the PMA parts have only been trickling in.  Converting to seperate mags is an expensive task, provided it can even be done legally. Check the type certificate data sheet. Some a/c were certified with both single and dual mag variations, soe were not.

[KSMooniac]

Mooney changed to the -A3B6 engine (non Dual-mag) late in the M20J production run, and this variant is on the Type Certificate as approved so it is an easy change.  A new prop control bracket is needed, and perhaps something else simple.  Lycoming used to have an up-charge for a different core, but I believe they've pretty much eliminated that in an effort to encourage conversions to the split mag engine.

[lukejb]

Cliffy,

Do you know what size or part number lock washer and nut are used for this and what the quantity is for these. I would assume that my AI that performs annual inspection would have these on hand since he works on a number of different M20J but i would like to go ahead and purchase some from Aircraft Spruce if possible just so they are on hand and i can be certain that they are used when reinstalling the dual mag.

Thanks,

Luke

[jetdriven]

7/16 internal tooth star lock washer.

[cliffy]

Nuts don't change but jetdriven has the answer again!  :-)  7/16 internal star lock washers (AN aircraft quality only please)

1 lock washer per nut, 2 nuts per mag. A special heavy washer goes on the stud after the mag goes on, then the lock washer and then the plain nut. 

[lukejb]

Thanks! Is this what you are talking about? http://www.aircraftspruce.com/catalog/hapages/lockwasherstars.php If so stainless or cad plated recommended for this?

[jetdriven]

Curiosly, the latest edition of SB 1508 shows no standard washer, only the lock washer. I recommend the newest version of the clamps, even if they are 37$ each.

http://www.lycoming.com/Portals/0/techpublications/serviceinstructions/SI%201508C%20(02-10-2011)/Dual%20Magneto%20Attachment.pdf

[lukejb]

That was one of the items on our checklist for the mag. Ensuring that these clamps were on it.

Thanks!

[cliffy]

By washer I was referring to the clamps. My boo boo. Some mags have very thick washers and some have stepped clamps. 

jetdriven does it again :-)

Cad plated star washers as shown.

[KSMooniac]

Just buy a bag full of washers... 10-20 of them and leave them in your tool box and give two to the mechanic every time they monkey with the mag.  That way there is no temptation to re-use them.