The International Cessna 170 Association

A friend put 12 new Champion plugs in his engine (plugs came with a new set of Slick mags). Engine ran somewhat rough so plugs pulled and checked. Reinstalled and no improvement. (Don't know if they were cleaned in a plug cleaner or not, but shop has that equipment so I would think they did) He put in 6 fine wire Champions and sent the 6 that didn't ck out good back to Champion who after a lengthly delay agreed to send him 6 new plugs now and to give him another 6 if he goes to their booth at S&F in April. They claimed they cleaned the plugs and they tested OK, suggesting that when installed, thread lube probably got on the electrodes and shorted them out. I have always been cautioned not to let the lube get on the electrodes for that reason.
My question is that if lube did get on the electrodes (they say three were shorted) would cleaning the plugs return them to operating correctly?

I don't know what kind of thread lube was used..but the Champion lube is a graphitic-liquid and you'd have to saturate the plug thoroughly to cause a short, it would seem. I use Permatex Anti-Seize on my plugs. A bit brushed onto the main threads and a bit also on the upper threads where the harness fits onto them. Never had a problem at all.

Although that is possible that thread lube grounded the plug, cleaning them will often remove that part of the equation. The problem with plugs is that they are fickle. You dont know the history of the new plug. For example, just because they are new it does not mean they were not dropped and the insulators are damaged. best way to tell the condition of the plug is to check the resistance. if they are over 5K they are junk. Even if they are new. Bomb testing them will give the best test for the plug after cleaning. a lot of shade tree mechanics dont do this test but you said the shop does. YMMV Doug

I have a Mil Spec somewhere for plugs. For quite some time Champion did not make the requirements which is 5000 ohms. I am flying blind here so may be inaccurate. Champion for years said this was not true. I have heard they eventually changed the resistor to meet the specs. You can tell the difference in the old plugs had a slotted screw head in the bottom of the barrel. the new ones do not have that and meet the spec. You can check it with an ohm meter. I switched to Tempest and have eliminated all problems with Chamion plugs. Clif Orcutt at Aircraft Magneto in Montana can shed further light on this subject.

Tempest claims their T556 “doesn't drip, and more importantly, won't inadvertently run down on the firing end of the spark plug potentially causing an environment conducive to fouling or even pre-ignition.”

I recently ran across an EAA video clip about applying heat transfer paste to Rotax plugs. (Yeah I know, pretty exciting video. Insomnia, what better cure than a video on heat transfer paste?) Anyway Rotax uses Wacker P12. The video advised not to use cheap substitutes which turn to powder when they get hot.

If you put the lube on the second thread instead of the end you wont have that problem either.

Fortunately I’ve not had a problem either and we don’t think that was
the issue with Champions. Must’ve been defective plugs. I switched to Tempest yrs ago and am happy with them. Thanks for the comments.

Here's what Lycoming says in their Service Instruction 1042AE:

Use a copper-based anti-seize compound or engine oil on spark plug threads starting two full threads from the electrode, but DO NOT use a graphite-based compound.

Continental's M-0 maintenance manual says to "use only manufacturer's recommended spark plug thread lubricant".

I can't help but criticize Lycoming's advice to use engine oil for a thread lubricant. It will "coke" (carbonize) and seize. IMO.

I hate service instructions that only say "what" and not "why". I know graphite is bad for steel at high temperatures, but aluminum too?

Oil seems like the worst thing to use. I've tried using anti-seize, but it's grease-based and also makes burned crud in the threads. Not as bad as oil, though.

The Permatex Anti Seize I mentioned earlier is specifically recommended for spark plugs by it's mfr'r, ...contains copper and graphite, ....and withstands tempuratures up to 1600 degrees . See the "Applications" Tab at the bottom of this page:

https://www.permatex.com/products/lubri ... bricant-2/