THE PLT REPORTED THAT DURING A PULL-UP, THE PROP WENT TO A LOW PITCH ANGLE & THE ENG WAS NOT DEVELOPING FULL POWER. HE NOTED THAT THE TACHOMETER WAS NEAR THE RED LINE & HE RETARDED THE PROP PITCH CONTROL & THE THROTTLE. ALSO, HE NOTED THAT THE OIL PRESSURE GAGE INDICATED NORMAL. THE PLT THOUGHT HE HAD ENOUGH POWER TO FLY TO THE EDGE OF THE FIELD TO DUMP HIS LOAD IN ORDER TO MINIMIZE THE CROP DAMAGE. HOWEVER, HE REPORTED THERE WAS INSUFFICIENT POWER TO CLEAR TREES. SUBSEQUENTLY, A FORCED LANDING WAS MADE IN THE TREES & THE ACFT WAS DAMAGED. AN EXAM REVEALED THAT THE #6 CONNECTING ROD HAD FAILED ABOUT 1 INCH FROM THE ROD CAP. THERE WAS EVIDENCE OF LOCALIZED OVERHEATING. THE #6 ROD RECEIVED SPLASH & SPRAY OIL FROM AN OIL PORT IN THE MAIN JOURNAL. THE MAIN JOURNAL BEARING APPEARED TO HAVE SPUN & CLOSED OFF THE OIL PORT, REDUCING COOLING OIL TO THE #6 ROD. THE PROP GOVERNOR RECEIVED OIL FROM THE SAME PORT. OBSTRUCTION OF OIL TO THE GOVERNOR WOULD ALLOW THE PROP TO DRIVE TO A LOW PITCH/HI RPM POSITION.