which goes back to the "walking" pin, id say the circlip has been pushed out and trapped below, or on the bottom rings, and thats why the score goes near to the top of the cylinder
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is it safe to assume that the crack was on the same side of the piston as the scores ?
bit chicken and egg really isn't it did it crack to release the circlip or did the circlip releasing cause the crack
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just like the rest of the guys have said..........................
by the looks off it the circlip has come off! and with that the pin as started to move ...........as soon as the pin worked its way out this would have put all the "load" on one side of the piston, ...................
IMHO.........this comes down to bad installation off the piston's i would say.........i think you need to take this up with who did the installation ................ and not the guy who SOLD you them ;)