Thoughts about Plug Wires

[DaV8or]

I have one plug wire that has the outside shielding scuffed away to expose the plastic insulation. It was rubbing on a metal hose ID tag. I have since solved the rubbing issue, but I guess I need to replace the wire. The wires I have are the older exposed metal shielding type.

I plan to do the 500 hour mag inspection and so it got me to wondering about just putting all new wires on while the mags are out. I guess the newer style Slick wire harness is about $400. Do plug wires wear out much? These have about 500 hours on them. In my old automotive days, we used to change wires frequently as they were cheap and brand and type mattered. I'm inclined to change them, but am I irrational?

The question you all might have is, am I having a problem? The answer is yes, sort of. Two issues with my Lycoming IO-360 A1A with Slick mags-

1. The engine has never run all that well LOP. The entire fuel system has been cleaned adjusted and inspected. The intake gaskets have been replaced. I installed new plugs. I have never done anything to the mags or wires. My injectors are stock and I'm not able as of yet to be able to run the GAMI lean test because of erratic fuel flow indications, but I'm working on that. The rough LOP could be the injectors, but it could also be ignition.
2. I recently had the engine start running rough in cruise and continued through taxi. Number 1 cylinder showed normal EGT, but low CHT. That means either ignition, or valves. Did a compression check and it was normal. Number 1 is the cylinder with the damaged plug wire. Checked both plugs and found lead fouling in the bottom of the bottom plug. Cleaned it out and taxied back for a run up. Run up seemed improved, but unfortunately, I couldn't fly because on the last run up, my prop cable connection failed. When it rains it pours I guess. I hope to have the prop fixed this week and I'll fly it.

Anyhow, I'm inclined to replace the plug harness in the pursuit of reliability and a good running engine that can run smoothly LOP. Is this crazy? Would you just replace the one wire, or the whole shebang? Is there a brand/type of harness that is better than another? So the lurkers can participate, there is a poll, but I would rather have opinions.

Thanks for the help!

[N601RX]

I purchased a new set with the 90 deg brass ends about 2 years ago. At the time they were cheap compared to others available, but have since been purchased by hartzell and the price has increased. Most mechanics have a boxful of old harnesses if you only need a single wire.

The ones with the AR in the pn have the angled boots.

http://www.aircraftspruce.com/catalog/eppages/aeroliteharness.php#review_tab

[Marauder]

Funny timing Dave. Going through the same discussion with my mechanic. I do a pre-annual of my plane before handing it off to the mechanic for the annual. I have one lead that I found on my airplane that was worn at the spark plug end. I asked about changing the entire harness out figuring that at 900 hours on this rebuild, it was time. He said save your money, I can fix this lead.

I'm not sure if he was saying this because he knows I am the President of the Cheap Bast&$rd Club, but I told him I have no run up problems and only found the lead going through the plane.

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[jetdriven]

Id replace the Slick harness for a Bendix harness, and put in OH Bendix mags as well. For the price of the 500hr mag inspection you can get Bendix mags.  perhaps it will run well LOP also.

[Guest]

Ditch the Slick mags and harness if you can. TCM Bendix is more reliable.

Glad my 720 can't use Slick.

Clarence

[carusoam]

Replace the old wires for sorta the same reason the automotive guys do... Newer materials will perform better over time...

That was my thought when I replaced eight wires on my O360. Took about an hour.... They got tied in place properly, the old wires were of unknown vintage, possibly original...?

16 wires... That's a winner Clarence!

[DaV8or]

Has there been any advances in wire technology in the last ten years or so? I noticed that what they sell now doesn't look like what I have. I guess there is no rule of thumb, or guidelines on wire life. One guy on another forum suggested that 1000 hours was when you should change them. Others seem to think as long as they test OK, run them forever I guess.

[cujet]

I'd simply replace the failed wire with a like kind new one. (if you can find one, or have one fabricated) 

 

Wires last a very long time, so it's quite likely your other wires are just fine. The problem is that it's now hard to find the components to make spark plug wires. What used to cost $20 in parts now requires an entire harness replacement at $400.