Is that a bit of damage aroung the gudgeon pin hole too?
Sorry if it's me but are the top rings on the other two pistons stuck?
If you're going to do a full recon of bearings, pistons and rings why bother what caused the prob as it is full of so many variables .. but do check out the crankshaft trueness of the con rods , bores & lub system etc. along with everything else to make sure nothing has dropped in from elsewhere..
how do you check that im only going to do the pistons un less i find something else wrong
I would offer that someone with your level of skill ( not being nasty either ) would be at a disadvantage doing it yourself for if you put the piston on the wrong way to the thrust side face or rings upside down ( if directional ) or put the conrods on the crank wrong you may end up trashing everything in a few seconds.
Have you looked online for the engine specifications or do you have them ?
how did you guess i have marked everything as it came out
but i need the work shop so it might have to be a quick fix
i have a mechanic coming tomorrow to have a look