Well the cylinder can sometimes become severely worn from dust and dirt in the air intake and it will out of round the cylinder causing it to rock a round a bit.I'd just se if it's bent and if not if it needs shimmed.
Have u checked 2 see if that is the right size piston? Cuz i saw what happened one time when the wrong size was put in and it looked exactly like that. Like 2 the T same cracks same look ill see if i can find the piston i got and take a pic but its scary how simaler that looks.
first thing to check is the crank rod..check for up and down motion..side to side also..that is either from a bent crank rod..or wrong piston was put in it..if the rod bearing is so worn out..it will cause a side to side problem..which in turn..puts to much stress on the piston's wrist pin area..soo..check your crank rod bearing play..start there..then check to make sure you got the right piston..from the looks of that piston..from what i've learned..it looks like the crank bearing is so worn..that on the down stroke..it smacked into the main crank..soo..check all the bearing's in the crank first.
Are you sure it hasn't been apart before? The inside of that piston looks pretty low mileage. Look at the crank real close too and see if you can see where it hit. It looks like it hit on both sides of that side of the skirt. I'd say contact with the crank counterweights. It had to be making some noise too.
yup jrl305..that's what i think..it hit the crank's counter weights..bad crank rod bearings..allowing to much slack on the down stroke..posb a bent crank rod..it could also have been undersized at the factory on the crank where the rod connects to..causing it to slam into the counter weights from to high rpm..either way..before you put the top end back together..put the new piston on..rotate the engine by hand a few times..and check for piston/crank clearance..if it hit's the crank's counter weights..your going to need to tear the whole bottom of the engine down..too check your crank play..grab the rod..try to move it up and down on the crank..without it turning on the crank..see what kinda play you have..you shouldnt have very plug play at all..now..after you check the up and down play..move the crank rod side to side..same goes here..you cant have alot of play on the side to side motion..some..but not much.