TM  1-1520-240-10            2-7-1 SECTION  VII.  POWER TRAIN SYSTEM 2-7-1.  General. Engine power is supplied to the rotors through a mechan- ical transmission system (fig, FO-1). This system con- sists of a forward , a combining (mix), an aft, two engine transmission, and drive shafting. An overrunning sprag clutch  is  installed  in  each  engine  transmission.  The clutch provides a positive drive connection to transmit power and permits freewheeling of both rotors when in an actual autorotation or during a simulated power failure. Because  of  the  freewheeling  feature,  no  drag  will  be placed on the rotors if an engine (or engines) fails. Power   from   the   engine   transmission   is   transmitted through  separate  drive  shafts  to  the  combining  (mix) transmission.  The  combining  (mix)  transmission  com- bines the power of the engines and transmits it at re- duced shaft speed to the forward and aft transmissions. Further speed reductions occurs within the rotor trans- mission. Two  AC  generators,  the  No.  2  flight  control  hydraulic pump, and the utility system pump are mounted on and driven by the aft transmission. The No. 1 flight control hydraulic pump is mounted on and driven by the forward transmission. 2-7-2.  Transmission Lubrication Systems. The  forward,  aft,  and  combining  (mix)  transmissions have independent main and auxiliary lubrication systems which  operate  concurrently.  Each  transmission  has  a filter with an impending bypass indicator. If the differential pressure across the filter exceeds 15 to 18 psi, the by- pass indicator will extend to indicate a partially clogged filter. When the differential pressure reaches 25 to 30 psi, lubrication oil will bypass the filter. Refer to table 2-15-1 for transmission oil system capacities, oil specifications, and servicing procedures. 2-7-3.  Forward Transmission. The  forward  transmission  lubricating  system  supplies lubricating oil to the gears and bearings in the forward transmission.  Main  system  oil  flows  from  the  sump, through  the  main  oil  pump,  oil  filter,  cooler,  and  a  jet protection screen to jets from which the oil is discharged to the various gears and bearings. Auxiliary system oil flows from the auxiliary sump through the auxiliary oil pump, and the auxiliary system filter to separate auxiliary oil jets. An oil cooler mounted on the aft end of the trans- mission around the input pinion cools mains system oil. Air is forced through the cooler by a transmission-driven fan. 2-7-4.  Aft Transmission. The aft transmission lubricating system supplies lubricat- ing oil to the various gears and bearings in the aft trans- mission and to the aft rotor shaft bearing. In addition, the main lubrication system circulates cooling oil through the two AC generators on the aft transmission. Transmission oil  flows  from  the  sump  through  the  main  lube  pump, main filter, cooler, and the jet protection screen to jets where the oil is sprayed onto the various gears and bea- rings. In addition, after the oil leaves the jet protection screen, alternate paths routes some of the lubricating oil to the aft shaft bearing and cooling oil to the generators. Auxiliary system oil flows from the auxiliary sump through through the auxiliary pump and filter to the various gears and bearings. The auxiliary system does not lubricate the aft shaft bearing or the generators. An oil cooler mounted on the aft end of the transmission cools main system oil. Cooling air is drawn through the cooler by a transmis- sion-driven fan. 2-7-5.  Combining   and   Engine   Transmission   Lu- brication Systems. The combining (mix) transmission contains the oil reser- voirs to supply lubrication oil to the various gears and bearings in the combining (mix) transmission, No.1 en- gine transmission, and the no. 2 engine transmission. Two  lubricating  pump  assemblies  with  four  elements each are within the combining (mix) transmission: left- pump assemblies provides main lubrication to the com- bining (mix) transmission and the no. 1 engine transmis- sion.   The   right   pump   assembly   provides   auxiliary lubrication to the combining (mix) transmission and lubri- cates the No. 2 engine transmission. Each pump assem- bly contains two pumping elements and two scavenge elements. Combining transmission main lubrication oil flows from the combining (mix) transmission oil reservoir through the   left   pump   assembly,   filter,   cooler,   jet  protection screen, and to the jets which spray the oil onto the vari- ous gears and bearings. One of the scavenge elements of the left pump assembly returns the oil from the combin- ing  (mix)  transmission  sump  to  the  combining  (mix) transmission  oil  reservoir.  The  auxiliary  lubrication  oil flows from the combining (mix) transmission auxiliary oil reservoir to the right pump assembly, auxiliary lubrication filter, and to the jets which spray the oil on the various gears and bearings. One of the scavenge elements of the right pump assembly returns the oil from the combining (mix) transmission sump to the combining (mix) trans- mission oil reservoir. the right pump assembly does not route oil through a cooler. No. 1 engine transmission oil flows from the No. 1 engine transmission oil reservoir on the combining (mix) trans- mission through the left pump assembly, filter, cooler, jet protection screen, and to the jets which spray the oil on to the various gears and bearings. One of the scavenge elements of the left pump assembly returns the oil from No. 1 engine transmission sump through a debris indicat- ing screen and back to the No. 1 engine transmission oil reservoir. No. 2 engine transmission oil flows from the