My sons KX 65 locked up one day and I took it apart and found that the piston skirt was broken. The bore was also damaged so I sent it out to be welded, plated, honed and purchased a new piston. I put the bike back together and it ran great for a month before it locked up again. I took it apart and found the piston skirt is broken again. Does any have some information on what I should be looking for that would cause this? I have attached some photos. Any help would be greatly appreciated!