a14 pistons have a larger distance from the gudgeon pin to the crown, therefor if u use an a14 piston in an a15, it protrudes out the top of the block. machine 2.5mm off the top of the piston and u end up with pretty much a flat top piston. However the top ring is close to the crown. i machined down an old piston to show what i am talking bout.

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