16-21.PISTON PUMP - REPAIR (Cont’d) b.  Measure face thickness of each shoe. The face thickness of all shoes must be within 0.001 inches of each other. 7.   INSPECT CYLINDER BLOCK (17). a.  Inspect cylinder block bore for wear,  scratches,  and/or erosion between cylinders. Check the spring,  washers,  and retaining ring located within the cylinder block for wear. b.  Check each cylinder block bore for excessive wear by sliding the piston and shoe subassemblies through the bores. If binding is evident,  clean cylinder block and piston,  lubricate parts with clean hydraulic fluid and again check for binding. 8.   INSPECT CHECK VALVE (43). a.  Press check valve (43) against spring (44).Valve (43) should return and hold firm against seat (42). b.  If replacement is necessary, spring (44),  valve (43),  and seat (42) must be replaced as a set. ASSEMBLY 1.   IF REMOVED,  INSTALL TWO PLUGS (50) TO COMPENSATOR (1). 2.   IF REMOVED,  INSTALL ALIGNMENT PINS (49) INTO HOUSING (6). 3.   INSTALL NEW DRIVE SHAFT BEARING (38) AND SEAL (41). a.  Use fabricated tool (App.  C,  Fig. C-12) and an arbor press to press shaft (15) through bearing (38). Press shaft until bearing (38) bottoms against drive shaft (15) shoulder. 16-134