4-33. PISTON AND CONNECTING ROD MAINTENANCE (Cont)
Do not allow ends of oil ring 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.
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
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.
. 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 groove with gap 180° from gap in expander. Install upper half (23) in lower groove wtih
gap 45° from gap in Iower half of ring and 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.
not spread rings any more than necessary to slip them over piston. Ring breakage
and overstressing will result.
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.