Ignition leads

So a few weeks back I posted here about large mag drops and electrical noise
on the radio. Many posters prognosticated that an ignition lead was to
blame, and when the mechanic opened the cowling, this was confirmed- one
lead gone beyond repair.

He put all leads on a tester, and said the other 7 looked fine, so we
elected to simply replace the one bad lead, which cost $45 for the lead and
about $130 for the labor (2 hours IIRC). We initially siggested replacing
the whole harness, as 7/8 leads were original 1979 vintage, but the mechanic
siad, "why bother?"

A week later two of my partners are flying back from a short tripe
(basically one hour after the bird came out of the shop) and back comes the
magneto drop and popping sound. They find a mechanic, and sure enough,
another lead's shot. So now we're back to replace the whole set and keep the
two newer leads as spares.

Is the moral of the story that on any repair that involves multiples of the
same item (plugs, valves, etc.) to just replace the whole set if they're
more than X years old? We've also got cylinders reading 63, 68, 70, and 73.
If one dips down, do we just top the whole thing (it has about 1800 tach
time) or just replace the bad jug? Or do we declare surrender and major it,
even though it's a 100% part-91 airplane and the engine doesn't turn into a
pumpkin when the meter hits 2000?

I don't mind spending money to fix things once, that's just life, but
there's nothing I hate more than fixing the same damn thing twice.

-cwk.

I don't mind spending money to fix things once, that's just life, but
there's nothing I hate more than fixing the same damn thing twice.

Nothing worse than sending good money after bad, but that just seems to
happen every time I try to save a few bucks.

This rule holds true on almost everything, from remodeling the inn, to
buying appliances, to working on my plane. Every time I try to take the
cheap way out of a problem, it comes back to bite me. I've finally gotten to
the point where fixing it right is my first inclination, but then I always
wonder if I couldn't have gotten away more cheaply.

Bottom line: You can't win.

;-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

On Thu, 30 Sep 2004 21:49:37 GMT, "C Kingsbury"
wrote:

do we just top the whole thing (it has about 1800 tach
time) or just replace the bad jug?


What kind of engine is it and are you making any metal? Do an oil
analysis or two to give yourself a little better idea of what's
happening inside the engine. If all seems good and its either an
O-470, or O-540, I'd top it. Other engine models I can't really
comment on from experience.

From a monetary point of view, if you've got 3 partners and are
running a 4 cylinder why not chip in 5K a peice if/when needed and get
a complete overhaul. I'm not a big fan of squirling money away every
flight hour toward O/H, but when you're as close as you are and know
something's coming, why not plan ahead and start to save.

HTH.
z

On 30-Sep-2004, "C Kingsbury" wrote:

We've also got cylinders reading 63, 68, 70, and 73.
If one dips down, do we just top the whole thing (it has about 1800 tach
time) or just replace the bad jug? Or do we declare surrender and major
it, even though it's a 100% part-91 airplane and the engine doesn't turn
into
a pumpkin when the meter hits 2000?


I think it depends on what is wrong with the "bad" jug. If it has no cracks
or other problems besides low compression, my inclination would be to have
it (the jug) overhauled (i.e. reworked) if possible. We had a very similar
situation with the IO-320 in our Skyhawk when it had about 1750 SMOH. We
pulled the jug, sent it out for repair, and flew on it with no preblems for
the next 300 hours, until general engine condition (and calendar time SMOH)
dictated a major,

--
-Elliott Drucker

I had a similar event happen last year when I only got "2 green" on
lowering the LG. The plastic housing on one gear down switch had
become brittle with age and broken the wire. That landing made me
sweat enough to just replace all 3 wiring assemblies when I got it on
the ground. The question gets harder to answer as the cost goes up
(jugs), and as Jay says you can't win. "It all depends..." My
general rule on a 1969 aircraft is "replace 'em all" when one goes
bad.

Those compression numbers sound like our Lyc 0320 E2D powered 172M.
It never has had particularily good compression since it was new 25
years ago. If we get one that won't make 60/80, we check it again 5
or 10 hours later and it always is up again. It has been doing this
to us for 20 years.

I've always felt that a moderately (say 50/80)low compression number
without any other obvious cylinder trauma isn't automatically a reason
to pull a jug, at least not without a later recheck. If there are
other signs like high oil consumption, plug fouling, or rough running
etc then I could see pulling it.

wrote:
: I've always felt that a moderately (say 50/80)low compression number
: without any other obvious cylinder trauma isn't automatically a reason
: to pull a jug, at least not without a later recheck.

If the compression is that low (basically, anything under 70/80), there's a
definitive REASON for it... leaking valves or leaking rings. Neither one is a good
thing, but the valves in particular are a very bad thing. Rings may be gunked up or
never seated, but there's something wrong if compression is that low.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************