I’m wondering, why lycoming says in their SI 1042AH says DO NOT use a graphite-based compound. ?
Tempest compound designed for spark plugs is graphite based…
Do you mean the anti-stick compound you brush onto the threads?
I never thought about it before, but graphite can cause aluminium to corrode and marking up parts with pencil is a big no-no. On the other hand, engines are hardly short on Carbon deposits.
I had to put bronze inserts in my cylinder heads (VW, not Lycoming) because the threads were starting to corrode. I have no idea whether this was related to using graphite on the plugs or not.
I use this stuff (I think). No idea what it is based on.
I briefly used the copper based stuff and then found a dramatic jump in copper in oil analysis 
Might be that one; the Champion one seems identical.
URL fixed.
SI1042AH_Approved_Spark_Plugs_pdf is what says to not use graphite, but doesn’t say why.
If you use the copper compound, forget drawing much conclusion from oil analysis…
For years I used cooper based stuff however since I started to make oil analyze I have elevated cooper… I (and any of my customers) never had problems about corrosion/threads etc.
So I decided to swap to ultra professional stuff from tempest but its graphite based and this is forbidden by lycoming SI.
No idea what to do..
The plugs I use (UREM37BY) have plated threads, and I think that’s true for other aircraft plugs at this point. At least in theory (referencing automotive practice with plated threads) that would mean they don’t need to be lubricated for installation – it is for example
explicitly not recommended for plated automotive plugs. The Lycoming SB recommends either copper based thread lubricant or engine oil. With all that in mind and if you don’t want to use copper based lubricant, I’d chase the threads at installation with an appropriate tap to clean out lead deposits at the cylinder end of the female thread, and lubricate the male threads with engine oil. The plugs come out often enough that I don’t see that engine oil in combination with plated threads on the plug is going to cause any issues.
Uhm. Perhaps. Regarding this plating I would be carefull because on cleaning spark plugs thread is also cleaned, usually by metal brush. It can partially remove surface and plating. I think automotive plugs are not used for so long time as aircraft (so many in and out’s).
Metal brushes are not good because they leave bits of steel (the brush wire) everywhere, and that corrodes aluminium very well.
What does corrosion look like, in the cylinder head? I don’t think I have noticed this.
On reflection it may be that on my cylinder heads, bits of thread had bonded to the plugs and so gradually got removed over the years. Perhaps this is related to corrosion. Last night I found that the US Air Force has apparently banned all graphite lubricants due to the risk of corrosion – apparently only really an issue if you are next to the sea.
