I am on my third set of these.
The first set were Champion RHM38S and they had the big problems with the resistors disintegrating. (Champion later claimed to have fixed this). But the electrodes never showed any wear, after about 1000hrs.
The second set were Tempest URHM38S and they did another 1000hrs, at the end of which they also showed no wear.
The third set will come with my new engine. I could have re-used the last plugs but decided one should change plugs when fitting a new/overhauled engine. Not a cheap decision!
So I have the second set (of 12) if anybody wants to buy them. But would anybody want them? I suppose the Q is whether plugs are considered to have a life limit. I can clean them up and put them on Ebay…
It isn’t just the electrodes. There is also the ceramic insulator, etc.
Obviously I could keep them as spares but they seem to last for ever and in the TB20 the insulator never seems to break.
US owners claim 2000h problem free.
What do they say happens to them at 2000hrs? It would surprise me it would be electrode erosion, since none is evident at approximately 1000 hrs.
There have been problems with some plugs in some engines. The SR22T has suffered massively with cracked insulators – that was all over the US sites for years. But that engine uses a different plug, with a longer reach and more of the insulator exposed to the combustion.
To answer myself 
I bet nothing happens to these plugs at 2000hrs… not in a non-turbo engine anyway.
I have put my extra 12 plugs under Classifieds for €200 plus delivery
I just bought a set of new plugs so I could pre-clean a set to keep in the tool box – that way, when I do my 50 hour check I can slam a “cleaned” set in as the oil drains…………which is handy when doing it on the Airfield in the open!
Also to be deliberately provocative ………….I bet nothing happens to your (in your case…..regularly used) engine either at 2,000 hours either Peter! Perhaps you are scrapping engines at the safest part of their life? 2,000 – 3,000 hours.
It’s a shame there are no statistics on regularly used engines well past TBO. All of the reading I have done hints that they are probably a lot safer than a 0-400 hour old engine? (As long as they have not been left standing, no corrosion, the filter is cut open, 25 hour oil changes, compressions are checked etc)
So my argument is running a known, regularly used engine “on condition” is a good idea, not to save money, but is actually safer than a new one!?
BTW – thanks for a really interesting forum – I have learnt a lot.
The spark plugs have found a new home
I have 3 spares also which I think is enough.
