Cranky mag?

[Fendermandan]

On mag check rpm drop is good on the left mag but it was struggling with firing if the plane was not flown in a week. If it did fly then it was ok. Last few days it started again even the plane was flown the day before and again after the higher 2000 rpm goes to normal. The mags were replaced last Fall and have 130ish hours. Just asking to get idea where to start looking before AME goes artsy on me


What do you guys think?

[Colonel]

Hard to tell without more information, but ...

With 130 hrs, the points and condensors [i]should[/i]
be ok on the mags.

How old are the plugs?  If they are showing any
signs of age at all, I would change them.

Also, buzz out the high tensions leads with a
tester.  And inspect them for damage generally
caused by abrasion.  If one of them starts
grounding out, the spark's not going to make
it inside the cylinder.

Also, I would pop the caps on the mags, and
inspect them for anything going wrong inside -
carbon, heat damage, etc.  Point contact surface
ought to be perfect.  Ensure that the mags are
bolted on tight and check the timing - make sure
both points open at the same, correct time.
Make sure the bearings aren't shot on the mags.

It's probably not the coils but you never know.

[Strega]

If you ares somewhat handy electrically, and have access to an oscilloscope, put the scope on the p lead and take a look at the ignition primary waveform.  easy to see what is going on... (ever wonder why there was a scope built into the panel on a lot of large piston engine transport aircraft)

[DonutHole]

Throw a heater on the mags for a few hours before your next flight (a flight you would expect the condition) then try a normals start and mag drop check.

I have seen condensation moisture cause premature issues with mags in the past.

[cgzro]

"130hrs" - could still be the capacitor, they dont always replace it during overhaul.
Failure mode is misfiring at higher rpms (shorts at higher voltages) but ok at lower rpms. Your mechanic wont debug it but simply send the mag off for a rebuild. Me id cut the capacitor wire and try it. $25 for a new one!

[Fendermandan]

Thanks for replies, I'll go loot at it tonight

[Colonel]

Let us know.  An airplane that sits outside in the rain and
sun and snow and ice, is a completely different one than
is in the hangar and covered with dust and birdshit  ;D

[img width=500 height=374]http://rangerairfield.org/wp-content/up ... n_barn.jpg[/img]

At my old airport (where that picture is NOT from) there
was a terrible problem with birds drilling holes - big ones -
in the fabric aircraft in the old flat-top hangars with no doors.

People were wondering if they were punched by falling
icicles, but I think it was Woody.

[img width=500 height=421]https://s-media-cache-ak0.pinimg.com/73 ... eckers.jpg[/img]

The wonderful thing about parking outside is the
bird's nests in the spring:

[img width=500 height=375]http://toritrueflight.com/wp-content/up ... rdnest.jpg[/img]

Paint that foam red and stuff it in all the corners!

[Gravel Digger]

Pretty great advice for the price, AND with pictures, so that guys like me can follow along.


This gets my highest rating: two fingers and a thumb.

[Colonel]

[quote]my highest rating: two fingers and a thumb[/quote]

[img width=333 height=500]https://s-media-cache-ak0.pinimg.com/73 ... -girls.jpg[/img]

People get upset when I post pictures of interesting
aircraft, like that one.  DJ doesn't like ex-military
aircraft or biplanes, for example.  He's hard to please.

I'm a little worried what you would do, with two fingers
and a thumb in that situation.

[img width=500 height=472]http://www.bowlerx.com/media/Basic%20Dr ... 016(1).jpg[/img]

[David MacRay]

Holy smokes! Was that picture taken in strega's mythical hanger?  8)