What caused my melted piston?

[Tomas Wallin]

As some of you know I melted a piston in the beginning of summer, I never found any answer to why but today something struck me...

Would a loose spark plug might been the cause? Or was it an effect of what happened. Both from lack of heat transfer and also maybe from causing a lean mixture due to the bad seal.

When I removed the spark plugs after the incident I found that #6 was loose but I always thought that was caused by the detonation or the heat, but is that really that common?

One thing that always bugged me was that all the other cylinders looked so good and this melted, why would #6 get so lean and no other???


I have plenty more pictures of the pistons, plugs, valves etc...



It's a carbed (2x Holley 800cfm) 509ci with Superchiller and 8-71 with 9.5PSI boost@6000rpm. Iron heads and 8.3:1 in compression, very little total run time on motor since rebuilt and 10minutes run time since dyno (warmup)... This happened at wot.