Originally Posted by DanH
Bruce, if it makes a difference, I can't find any reason to replace the IKH27's until 200+ hours. It's typically been every other annual, but given how little I've been traveling recently, it might turn into three or even four years.
This 213 hours. The ground electrode has lost material near the tip, on the side facing the center electrode, which has eroded hardly at all. The result was increased gap, but no difference in operation. They could have been re-gapped and run more.
To expand on the post from DanH, I’ve read post on the VAF that indicate auto plugs should be discarded at 100 hours or once a year. I did so at first, but they always looked good and ran fine. I decided to run mine for as long as I could tolerate. At 350 hours I finally decide to replace them not because they failed but because I could. At 350 hours they had about twice the wear (on the ground electrode) show in the picture from DanH. They still ran perfectly well. You may consider leaving them in longer and monitoring the ground electrode.