[Oz-mooney] Magneto inspections/overhauls

Sat Oct 27 05:40:34 CDT 2007

While on the subject of magnetos....the "J" has the so called dual mag (2 
magnetos on the same drive shaft) on the IO-360-A3B6D. This can be a 
cantankerous magneto to work on. When it came time to overhaul my engine a 
year ago I elected to convert to the IO-360-A3B6 which uses two single mags, 
either Bendix or Unison. This engine is listed on the "J" type certificate 
so no STC is required. Unfortunately Lycoming considers this to be an 
"upgrade" and charges a premium to trade in the A3B6D for the A3B6. Also, I 
don't believe that the A3B6 is used in many aircraft so it isn't easy to 
find. My A3B6 was actually converted from an A1B6 (used on the Cessna 
Cardinal). Was it worth it? No problems so far, and I noticed that according 
to the MAPA Log price guide there is a small premium in calculating value. 
The other nice consideration is that if I have a mag problem it will be much 
easier to find a replacement or repair the single mags.

Peter R
N201CM YHOX

----- Original Message ----- 
From: "John Hillard" <johnhillard at westnet.com.au>
To: "'Australian Mooney Pilots Assocation List'" <oz-mooney at mooney.org.au>
Sent: Saturday, October 27, 2007 7:09 PM
Subject: RE: [Oz-mooney] Magneto inspections/overhauls

> Peter/Mike,
> Your discussion regarding magnetos prompted me to check the status on my
> aircraft - not sure whether you use the same magneto as the J.  The 
> service
> manual for the J appears to require overhaul every 4 years but there is 
> also
> AD96-12-07 that requires inspection every 500hrs.  Is there any difference
> between an inspection and an overhaul for these Bendix magnetos?.
> While looking this up I also found an example of magneto problems having
> fatal consequences in the Uk - interesting read in the context of your
> discussion -
> http://www.aaib.gov.uk/cms_resources/Mooney%20Aircraft%20Corporation%20M20J,
> %20G-EKMW%2011-06.pdf
>
> Regards
> John
>
> -----Original Message-----
> From: oz-mooney-bounces at mooney.org.au
> [mailto:oz-mooney-bounces at mooney.org.au] On Behalf Of Michael Keating
> Sent: Saturday, 27 October 2007 10:26 AM
> To: 'Australian Mooney Pilots Assocation List'
> Subject: RE: [Oz-mooney] Magneto inspections/overhauls
>
> Peter,
>
> I too had many problems with a magneto. Initially thought to be a 
> recurrent
> fouled plug due excessive ring wear etc. That was partly the case and so I
> undertook a top overhaul. Of course once you start reassembling things,
> other things go wrong and so the overhaul blew out from 15K to 24K.
>
> However, after all said and done, the problem recurred and always with the
> right mag which coincided with the bad pot and fouled plug etc.
>
> The mag was pulled and serviced and the points were noted to be melted. 
> This
> was done twice and I was blamed for running the engine too lean and hot at
> the holding point trying to clear the "fouled plug". Even the JPI 
> indicated
> it was a fouled plug (to this dumbcluck anyway).
>
> When it happened yet again we went back through the logbook and noted it 
> had
> been happening to the same mag for years and it had been serviced many
> times. They then decided to pull a few more bits out and noted overheated
> grease in the guts of it somewhere (abdominal guts I know, maggy guts I
> don't!) The bottom line was they felt the bearings had been shimmed out to
> much by the factory when the mag was overhauled when the new engine was 
> put
> in 900 hrs ago in 98. The 'theory' is this caused the bearings to overheat
> and transmit the heat up the duff or something causing the points to
> overheat and melt and therefore not open properly.
>
> Bearings re-shimmed etc and all problems solved. Now, I am not saying I 
> did
> an unnecessary top overhaul, God forbid, but I think a lot of the problems
> we blamed on the poor engine were actually the maggy. When the pots were
> pulled they did need doing and I elected to put complete new cylinder &
> piston kits in rather than oversize.
>
> For what its worth, the extra cost went into the maggy overhaul, 
> alternator
> then new alternator gear rubber/clutch, which failed yet again within 25 
> hrs
> and had to be replaced, overhaul of the fuel pump which sprung leaks on
> reassembly after the top overhaul, new baffles, new vac pump which failed 
> on
> last flight at FL165 above cloud en route to top overhaul and probably a 
> few
> others that I have blocked out due to pain.
>
> Why oh Why we still muck around with maggys when electronic ignition is so
> much better I have no idea - apart from the initial cost. Probably the 
> same
> reason we still muck around with avgas instead of jet A1 in our turbines!
> Mind you, Spall burns up to 180 LPH in the climb and 115 in cruise but can
> do trans-continental in 5.5hrs or so I think.
>
> Cheers
> Michael
>
> -----Original Message-----
> From: oz-mooney-bounces at mooney.org.au
> [mailto:oz-mooney-bounces at mooney.org.au] On Behalf Of Peter Wordsworth
> Sent: Friday, 26 October 2007 8:04 PM
> To: AMPA
> Subject: [Oz-mooney] Magneto inspections/overhauls
>
> Just to update my magneto problem from several days ago:
>
> It is evident 500 hour magneto inspections are not magneto overhauls.
> For a "new" 500 hour magneto it is likely only the points would be
> changed. That may be the case at 1000  hours as well (at least that's
> all that was done to mine).
>
> The failure of my left mag appears to be due to a failed capacitor
> which caused pitting of the contactor points. The failure occurred 40
> hours after the 500 hour magneto inspection (total engine time just
> over 1000 hours.)
>
> I decided to have the right mag pulled yesterday and that too had a
> capacitor which, while functioning, did not come up to spec so it was
> replaced as a precaution.
>
> I think it's totally unsatisfactory that capacitors are not replaced
> at each 500 hour interval, particularly given the relatively low cost
> and critical nature of the item.
>
> Total cost of this exercise was $990 including GST plus one week's
> down-time. It was just lucky that it did not happen a long way from a
> workshop or the cost could have been thousands.
>
> Peter
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