The ignition harnesses on our Aztec are not the newest items on the airplane
by any means. In fact, if somebody told me that they were original, I
wouldn't be able to refute it. Our's show some fraying of the outer cover,
some of the cigarettes are looking pretty old, showing fatigue, some of the
contact springs look tough, ect. Relatively speaking, new harnesses are
also not the most pricey items I've investigated, especially for the
performance that we get out of them.
So, what say the group?
Replacement Ignition Harnesses...
Who's replaced them?
Reason(s)?
Engine Make/Model?
Airplane Make/Model?
Straight or 90 degree?
Standard or all weather?
Best or worst brands or manufacturers?
Custom features or wire sizes?

Thanks as always.
Jim

On Thu, 26 Jan 2006 13:03:16 -0600, "Jim Burns"
> wrote:

>Replacement Ignition Harnesses...
>Who's replaced them?

Me.

>Reason(s)?

You name it. old-and-trashed, oil soaked and deteriorated, burnt,
abraded by water, corroded hardware, chafed, pinched, cut..primarily
because I allegedly got paid to do it.
..
>Engine Make/Model?

Pick one. 4-to-1 Lyc-to-TCM

>Airplane Make/Model?

Every "modern" Piper except a TCM Malibu, lotsa Cessna/Beech singles,
couple of Barons.

>Straight or 90 degree?

Both, depended on the install.

>Standard or all weather?

Both, depended on the install. Don't recall ever "converting" one from
standard to all weather.

>Best or worst brands or manufacturers?

Standard Unison/Slick harnesses are inexpensive and relatively easy to
repair, you can usually shorten them a couple times before poking in a
replacement lead. The silicone coating will gradually abrade and get a
little funky looking. Downside is they don't like the heat, and unless
they've changed the plug nut from the aluminium I'm familiar with, the
nuts will gall if you try to force them onto a boogered or corroded
sparkplug. Poking on a new nut on is fairly simple.

Have also used Bendix/TCM harnesses. They are pretty much mandatory on
turbo installs (w/90 degree elbows) depending on the wire routing so
you can keep them away from the exhaust stacks. They hold up a lot
longer, are a little tougher to repair/poke in a new lead. Cad-plated
steel nuts won't gall on funky plugs.

>Custom features or wire sizes?

Didn't have any real need for them.

On our Aztec's we always used the standard Unison harness with
straight (all weather) ends, secured the lowers to the intake pipes,
uppers to baffle bolts extending through the head to the "inside" with
plain nuts/lock washers. We used the Unison's 'cause when (not if,
when) an exhaust gasket blew or a stack dropped and semi-torched the
lead they were easy and cheap to replace.

Really doesn't make a big difference whose leads you use if you are
careful routing and securing them.

TC

In article >,
wrote:

(good stuff snipped)
>
> On our Aztec's we always used the standard Unison harness with
> straight (all weather) ends, secured the lowers to the intake pipes,
> uppers to baffle bolts extending through the head to the "inside" with
> plain nuts/lock washers. We used the Unison's 'cause when (not if,
> when) an exhaust gasket blew or a stack dropped and semi-torched the
> lead they were easy and cheap to replace.


This is a good reason to use blowproof exhaust gaskets -- I have never
seen one blow. I would never use the copper/asbestos type again!

Yes -- I have also replaced harnesses on my Johnson Rocket (Lycoming
O-435) a couple of times. I am currently using Slicks, but have used
Bendix. The most common problem I have had is carbon in the plug
cigarettes. Removing the cigarettes and cleaning with a Q-Tip and
lacquer thinner (both plug and lead) does the job.

I have the old "lunchbox" Bendix mags (SF-6LN-8), which have removable
fingers and a rotating drum distributor.

--
Remve "_" from email to reply to me personally.

On Fri, 27 Jan 2006 02:36:32 GMT, Orval Fairbairn
> wrote:


>This is a good reason to use blowproof exhaust gaskets -- I have never
>seen one blow. I would never use the copper/asbestos type again!

We yanked the exhaust every 100 hours (2-4 months) to free up the
ball- and slip-joints, inspect for cracks, and r/r the exhaust
gaskets. Used either the crappy c/a's or 2 stacked "all coppers". The
exhaust studs weren't long enuff to accommodate the heavy metal
blo-prufs, the flange, a washer and a nut. Am thinking toward the end
we were using low height stainless lock-nuts on 'em (from another OEM
exhaust install) and some would still would shake loose in 100 hrs.
When we switched to stacks with thicker flanges, the stacks lasted
longer, but it made the "thickness" problem worse.

At least we didn't have to worry about seized nuts...

TC

Jim Burns wrote:

> Who's replaced them?

Me, for one.

> Reason(s)?

One wire went bad and the second plug on that cylinder fouled due to the poorer
flame front (I suppose). It made for an unpleasant flight (SEL, 4 cylinder). I
did not want to repeat the experience and figured the rest would go soon, one at
a time. It would also be cheaper to pay the mech once, rather than uncowling 8
times.

> Engine Make/Model?

Continental O-200-A.

> Airplane Make/Model?

Cessna 150J.

> Straight or 90 degree?

Straight.

> Standard or all weather?

Standard.

> Best or worst brands or manufacturers?

Mechanic's choice - I don't know.

> Custom features or wire sizes?

No.

George Patterson
Coffee is only a way of stealing time that should by rights belong to
your slightly older self.

wrote:
/snip/
>
> Standard Unison/Slick harnesses are inexpensive and relatively easy to
> repair, you can usually shorten them a couple times before poking in a
> replacement lead. The silicone coating will gradually abrade and get a
> little funky looking. Downside is they don't like the heat, and unless
> they've changed the plug nut from the aluminium I'm familiar with, the
> nuts will gall if you try to force them onto a boogered or corroded
> sparkplug. Poking on a new nut on is fairly simple.
>
> Have also used Bendix/TCM harnesses. They are pretty much mandatory on
> turbo installs (w/90 degree elbows) depending on the wire routing so
> you can keep them away from the exhaust stacks. They hold up a lot
> longer, are a little tougher to repair/poke in a new lead. Cad-plated
> steel nuts won't gall on funky plugs.
/snip/

I have also replaced many sets on various aircraft over the years, and I
agree the TCM harnesses are very well made. I also really like the
Champion sets: They, too, have plated steel "B" nuts, offer 90 degree
ends on any application (makes for a neater installation, usually), and
have a very durable rubber wire coating. I've never seen a set break
down under normal use and care. Prices are reasonable, as well.

Happy Flying!
Scott Skylane
N92054