TM  9-2815-202-34 4-33. PISTON AND CONNECTING ROD  MAINTENANCE    (Cent) CAUTION l Do not allow ends of oil tina expanders to overlap. An overlapped expander will cause oil ring to protrude beyond allowable limits and result in breakage when piston is inserted in ring compressor during installation in cylinder  liner. l Do not cut or grind ends of expanders to prevent overlapping. Cutting or grinding ends will decrease expanding force on oil control rings and result in high lubricating oil  consumption. NOTE Upper oil ring groove requires a one-piece oil ring and lower groove requires a two-piece oil ring (upper and lower halves). (b) Install two ring expanders (21 ) in oil control ring grooves in piston skirt (14) with legs of free ends toward top of piston. CAUTION l l . . For all models except 7083-7391, scraper edges of all oil control rings must face down (toward bottom of piston) for proper oil control. . For model 7083-7391, the upper oil ring in the lower groove must face up (toward top of piston) for proper oil control. (c) Install upper and lower halves of lower oil control ring by hand. Install lower half (22) in bottom  c!roove with Qap 180° from  qa~ in expander. Install urwer half (23) in lower wove Wtih l (d) gap 45° km gap in Io;er half of ring ;nd scraper edge facing down. For” model 7083-7391 only, the scraper edge of the upper oil ring half (23) in the lower groove MUST face up for proper oil control. Using piston ring pliers, install upper oil ring (24) by positioning it over upper ring groove with scraper edge facing down. Align oil ring gap 180° from gap in expander (21). Press ring against gap side of expander to prevent ends of expander from overlapping. Then align ring with groove and release tension on ring pliers permitting ring to slip in position. CAUTION not spread rings any more than necessary to slip them over piston. Ring breakage Do and overstressing-will  resu!t. NOTE l Compression rings have one mark on top of ring and fire ring has two marks on top of ring. Clamp connecting rod of piston assembly in soft-jawed vise. . Model 7083-7391 has a  nongrooved-face  fire ring. All other models have a grooved face fire ring. (e) Starting with bottom compression ring, install two compression rings (25) and fire ring (26) using piston ring pliers. Install rings with marks toward top of piston. (f) Stagger ring gaps around piston 90° from each other. l 4-140 Change 1