Could be a conrod alignment issue. If the gudgeon and big end are not parallell the piston will be cocked over in the bore. From memory the specs for rod alignent are .001" difference over 6 inches, e.g. if you put a 6 inch bar through the gudgeon and another through the big end the difference between both ends should not exceed .001"
My first thoughts though were the circlips had fallen out, and I'm with Pete345673 and am a big fan of teflon buttons.
I mentioned vegetables once, but I think I got away with it...........
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