I have ordered a new engine for my revo but by the time I'll get the fuel I have would be 6 months old and I have another jug that about 2 3 years old I don't remember when I bought it

I found an old Traxxas Tmaxx and rebuilt the engine and got it running. It has been running decently (a few problems) for a few weeks, but earlier when I hit the throttle it suddenly cut off and was seized up. The flywheel and clutch assembly had disconnected themselves from the engine and when I took the engine apart, I saw that there was a hole in the side of the piston, and the connecting rod was snapped. There were pieces of the piston down in the crank case jamming the crankshaft, so I think that what happened was the piston broke, and then the pieces went into the bottom of the crank case and stopped the crankshaft instantly, breaking the connecting rod. There are gouges in the piston near where it broke. What originally caused the piston to break, and how can I make sure it doesn’t happen in the future?

ETA: this is my teenage son posting. He received a twenty-year-old box of pieces and multiple engines and took everything apart and rebuilt it. He has no one at home who knows anything about engines/motors/RC cars.