When observing a disassembled engine, the outer crown edges of all six pistons show signs of melting and erosion. What could be the cause?

Advanced timing can lead to excessive combustion temperatures within the engine. When the ignition occurs too early in the compression cycle, it can result in pre-ignition or knocking, contributing to higher thermal stresses on components such as pistons. The outer crown edges of the pistons are particularly susceptible to this extreme heat, causing melting and erosion as the temperatures exceed the material's limits.

In contrast, a dribbling injector typically causes issues like poor fuel atomization or fouling, which can lead to incomplete combustion, rather than directly increasing combustion temperatures to the point of causing significant damage. Retarded timing may lead to incomplete combustion and reduced efficiency, but it generally results in lower combustion temperatures compared to advanced timing. Fuel with high sulfur content can create corrosive substances and fouling, but it doesn't directly correlate with the thermal erosion observed on the pistons in the same way that advanced timing does. Therefore, the signs of melting and erosion on the pistons align most closely with the effects of advanced timing on engine operation.