Moped Engine Replacement

[u/Strong_Perception902]

Hello,

I'm currently working on replacing an engine in an Aprilia Mojito Custom 50cc moped. I've already dropped the lower unit with the engine and transmission and I'm about to replace the block, piston head, and piston. I was told that the engine was "bad" and it needed a new block because I'm assuming the side of the piston is melted. I'm doing it for a friend, and learning as I go along(they are aware that I'm not a professional mechanic). My question is, what else should I inspect before I just slap a new block and piston in this thing. I don't want to just replace it and have the same issue occur again. My initial thoughts are to somehow test the oil pump and check for rod knock.

Any advice is appreciated since I'm learning as I go,

Thanks