there are a couple of possibilities.
1stly these might sound simple but are you using the right temp plugs, and are they gapped the correct distance ???
I had a similar problem using 7's and switched to 6's :shock: but I have never had a problem since, I now other people running 8's and some even running 9's. So that might be something to look at.
Also another simple thing but worth mentioning. are you dropping the plugs in or are they slipping out of the socket before you get them in as if this is happening your damaging the plugs and what you have mentioned is the normal result. I suggest using long nose pliers and taking great care when fitting the plugs.
Also since this has happened I strongly suggest you get your hands on a bore scope or take your car somewhere and get the bore looked at as the little bits of metal might have caused some damage. Hopefully they burn up under the extreme heat and didn't damage the bore but best get it checked.
There are some simple things worth checking and looking at
