TM 55-1520-240-23-4 5-9 INSTALL ROTARY-WING HEAD     (Continued) 5-9 WARNING Dry cleaning solvent (E162) is flammable and toxic.  It can irritate skin and cause burns.  Use only in well-ventilated area, away from heat and open flame.  In case of contact, immediately flush skin or eyes with water for at least  15 minutes.  Get medical attention for eyes. WARNING Check rotor hub data plate serial number to ensure that it does not read UW3018.  If rotor hub (S/N UW3018) is found, do not install.  Immediately contact the technical point of contact in TB 1-1520-240-20-134. CAUTION Horizontal hinge pins with serial numbers of UW2407 and prior that do not have a suffix "A" vibro engraved after the serial number and with total time since new of  4800 flight hours or more must be replaced. NOTE Procedure is similar to install rotary-wing head with or without blades attached.   Installation of rotary-wing head with blades removed is shown. Task is similar for forward and aft rotary-wing heads.  Differences are noted in text.  Forward rotary-wing head can be installed with forward transmission package in workstand. 1. Remove barrier material from driveshaft (1). Clean splines (2).  Use cloth (E120) damp with dry cleaning solvent (E162). Wear gloves (E186). Wipe splines dry.  Use clean cloth (E120).  Apply thick coat of grease (E190) evenly to splines. Use brush (E86). 1.1. Check weight cavity drain hole in pitch-varying housing to ensure it is clear of debris.  Use pipe cleaner (E469). 2. Check that spacer (3) is installed on shaft (1) of forward transmission. 3. Check that centrifugal droop stop (4) is installed on shaft (1) of aft vertical shaft. 5-56 Change 2