My monster truck has an engine rattle and im not sure on what it is.. It wont idle and it lacks power. what could it be?

sounds like conrod is really worn out or crank pin. may alo be broken piston, might want to tear it apart and check it out. might save you a few bucks in the near future.

i have it apart and the rear crank Bering has some play and the piston pin has play in the piston but not the rod and the rod feels good on the crank