(25) Assemble pipe nipple (19) in oil sump (121); assemble pipe tee (18), street elbow (14), guide (17) to nipple (19). Place o-ring (16) on oil level gauge and install gauge (15) in nipple (19). (26) Assemble pipe nipple (13) in street elbow (14), attach hose (11) to nipple (13) and crankcase filter (7) with two hose clamps (12). (27) Install gasket (4)  air breather (1) using locknuts (3) and screws (2) to 1st stage cylinder head (5, Figure 8-14). 6-16  Air Cleaner  Assembly  (See  Figure   8-13).  The following paragraphs contain disassembly, cleaning, inspection.  repair or replacement and assembly instructions for the air breather assembly. a. Disassembly.  Disassemble the air cleaner assembly only to the extent necessary to repair or replace a defective part or parts. (1) Unscrew and remove wing nut (1) and washer (2) from top of air breather assembly. (2) Remove breather cover (3), element (4) and gasket (5) from base (6). b. Cleaning.  Refer to paragraph 6-3.a for general cleaning instructions. c. Inspection.  Refer to paragraph 6-3.b for general inspection instructions. d. Repair or Replacement.  Refer to paragraph 6- 3.c for general repair or replacement instructions. (1) If spot welds should crack or break loose on the stud or stud bracket of the base (1) repair by spot welding the crack or break. e. Assembly.  To  assemble the air cleaner assembly, proceed as follows:  (1) Place gasket (5) on base (6), install element (4) cleaner cover (3). NOTE Position breather cover (3) for proper breather hose attachment prior to tightening wing nut (1). 6-17.  First Stage Cylinder and Piston Group.  (See Figure 6-24  8-14).  The following paragraphs contain disassembly, cleaning, inspection, repair or replacement, and assembly instructions for the first stage cylinder and piston group. a. Disassembly.  Disassemble the first stage cylinder and piston group only to the extent necessary to repair or replace a defective part or parts. (1) Remove the piston and pin assembly (1) with piston rings (2) from cylinder (17). NOTE The piston and pin (1) are matched and are not to be replaced separately. Replace as an assembly only.  The compression rings (3) and oil control ring (4) are supplied in the form of a piston ring kit.  Replacement of rings should be by kit set only. (2) Remove cap screws (6) and lock washer (7); remove cylinder heat (5) gasket (8), valve assembly (9) and gasket (16). (3) To disassemble valve assembly (9), remove cotter pin (11), remove castle nut, and separate upper plate from lower plate. Fixing pin need not be removed from upper plate. NOTE The lentoid springs (12), valve ring (13), valve plate (14), spring plates (15), and the cotter pin (11) are supplied in the form of a valve repair kit and shall be replaced as such. (4) Remove valve plate (14), two lentoid springs (12), valve ring (13), and two spring plates (15). (5) The center bolt is secured in the lower plate with dowel pin peened over and neither should be removed. b. Cleaning.  Refer to paragraph 6-3.a for general cleaning instructions. (1) Remove caked grease or dirt with a nonmetallic brush after immersing part in solvent.  Scrape carbon, grease, and old gasket material from affected surfaces. (2) Clean parts with ’care.  Do not mar or scratch contact or seating surfaces.  Valve components should not be wire brushed. 6-24