TM10-3930-660-20 18-6. MAIN CONTROL VALVE ASSEMBLY  - ADJUST/REPLACE (Cont’ d) 7. INSTALL MAIN RELIEF VALVE PLUG ASSEMBLY. Screw main relief valve plug assembly (1) into port (2) and tighten. 8. REPLACE TRANSMISSION COVER, PARA.  16-6. ADJUSTMENT   - BOOM HOIST RELIEF VALVE 1. CONNECT PRESSURE GAUGE TO VALVE PORT. The main relief valve pressure must be adjusted above normal operating pressure to permit the boom hoist relief valve pressure to be adjusted. Main relief valve pressure is then returned to normal operating pressure at the end of this procedure. a. Remove main relief valve plug assembly  (l). b. Connect O to 5000 psi pressure c. d. gauge to plug assembly port (2). Remove acorn nut (3) covering slotted head adjusting screw. While holding adjusting screw, loosen and back off jam nut (4) which secures adjusting screw. 2. ADJUST MAIN RELIEF VALVE PRESSURE TO 3,100 psi. Engine may be operated at idle or full throttle when performing pressure tests. 18-24