THE PLT HAD COMPLETED A PRIVATE PLT GROUND SCHOOL COURSE & HAD FLOWN APRX 4.6 HRS IN A CESSNA 172 BEFORE FLYING HIS HOME BUILT ULTRALIGHT VEHICLE. DURING A TEST FLT, HE WAS MAKING A GO-AROUND FROM A TOUCH-AND-GO LANDING WHEN THE VEHICLE CRASHED. A WITNESS STATED THAT THE ULTRALIGHT PITCHED NOSE DOWN TO ABOUT A 45 DEG ANGLE & THE NOISE OF THE ENG INCREASED AS IT PITCHED DOWN. AN EXAM OF THE WRECKAGE REVEALED THAT THE SHORT ELEVATOR PUSH-PULL ROD HAD SEPARATED FROM THE ELEVATOR CLEVIS FORK. REPORTEDLY, THE HALF NYLOCK LOCKNUT WAS INSTALLED ON THE CONNECTING BOLT IN A REVERSE DIRECTION. THE MANUFACTURER'S ASSEMBLY INSTRUCTIONS DID NOT PROVIDE DETAILS ON THE JAM LOCKING OF THE NUT. ON 10/12/82, THE MANUFACTURER HAD ISSUED SPECIFIC INSTRUCTIONS FOR INSTALLATION OF LOCK NUTS, BUT REPORTEDLY, THESE PROCEDURES WERE NOT APPLIED TO THIS VEHICLE. HOWEVER, THE FAA A&P MECHANICS HANDBOOK (AC65-9A) DISCUSSED PROCEDURES FOR SECURING PUSH-PULL TUBE LINKAGES/FITTINGS/JAMNUTS. MAINT INSTRUCTIONS DO NOT ALWAYS DISCUSS SPECIFIC SAFETY METHODS.