Hole in Piston...

Hey riders, new on the board and hoping you guys can throw some ideas at me. I picked up a 79 KZ650 that wasn't running but looked real clean. I thought I got a good deal until I pulled the plugs and upon inspection with a flashlight saw a penny sized hole in one of the pistons. The hole looks to be broken out not burned. Bike has 25K miles on the odometer. I'll be pulling it apart this weekend and possibly looking for a replacement motor depending on how everything looks upon disassembly. Any ideas on what could have caused the piston to blow a hole? I've seen burnt but not broken before...

Anyone in Socal have a 650 or 750 motor for sale?

Thanks,
Brian

Sounds like the timing chain jumped and made the valves hit. Any other pistons hurt?

I won't know until I pull it apart this weekend but appreciate the response. I'll check the timing chain for tension and the other pistons for damage.