Melted #4 piston

[Kpro22]

After doing a compression test 60-120-155-155 , I took out the head and found this on piston #4. It’s looks like it’s been melted. Does the block needs a new rebuild?

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[jakk220]

Your engine was detonating. Very badly I might add. You will need a bottom end rebuild for sure. Either you were running too lean or too much timing.

 

[motomattx]

I would say that it was a lean condition, if it was timing they all would exhibit similar damage, probably either an air leak, or an injector seal leaking or an injector or driver not allowing enough fuel flow in that cylinder, have that injector cleaned and flow tested before even thinking of putting it back into service.