43
Disassembly/Inspection and Service
18 690 06 Rev. --
KohlerEngines.com
Replacement ring sets are also available separately
for STD pistons. Always use new piston rings when
installing pistons. Never use old rings.
Some important points to remember when servicing
piston rings:
1. Cylinder bore must be deglazed before service ring
sets are used.
2. If cylinder bore does not need reboring and if old
piston is within wear limits and free of score or scuff
marks, old piston may be reused.
3. Remove old rings and clean up grooves. Never
reuse old rings.
4. Before installing new rings on piston, place top 2
rings, each in turn, in its running area in cylinder
bore and check end gap. Compare ring gap to
Clearance Speci
fi
cations.
5. After installing new compression (top and middle)
rings on piston, check piston-to-ring side clearance.
Compare clearance to Clearance Speci
fi
cations. If
side clearance is greater than speci
fi
ed, a new
piston must be used.
Measuring Piston-to-Bore Clearance
Piston Detail
A
A
15 mm (0.5905 in.)
NOTE: Do not use a feeler gauge to measure piston-to-
bore clearance, it will yield inaccurate
measurements. Always use a micrometer.
Before installing piston into cylinder bore, it is necessary
that clearance be accurately checked. This step is
often overlooked, and if clearances are not within
speci
fi
cations, engine failure will usually result.
Use following procedure to accurately measure piston-
to-bore clearance:
1. Use a micrometer and measure diameter of piston
15 mm (0.5905 in.) above bottom of piston skirt and
perpendicular to piston pin.
2. Use an inside micrometer, telescoping gauge, or
bore gauge and measure cylinder bore. Take
measurement approximately 7.0 mm (0.2756 in.)
below top of bore and perpendicular to piston pin.
3. Piston-to-bore clearance is difference between bore
diameter and piston diameter (step 2 minus step 1).
Install New Piston Rings
C
D
E
F
B
A
A
Top Compression
Ring
B
Middle Compression
Ring
C
Oil Control Ring
D
Top Rail
E
Expander Ring
F
Bottom Rail
Piston Ring Orientation
E
A
D
B
C
A
Middle Compression
Ring Gap
B
Bottom Oil Rail Gap
C
Oil Ring Expander
Gap
D
Top Oil Rail Gap
E
Top Compression
Ring Gap
NOTE: Rings must be installed correctly. Install oil
control ring assembly (bottom groove)
fi
rst,
middle compression ring (center groove)
second, and top compression ring (top groove)
last. Oil control ring assembly is a three-piece
design, and consists of a top rail, expander ring,
and bottom rail.
To install new piston rings, proceed as follows:
Use a piston ring expander to install rings.
1. Oil control ring assembly (bottom groove): Install
expander
fi
rst then bottom rail and top rail last. Make
sure ends of expander are not overlapped. Adjust
ring gaps.
2. Middle compression ring (center groove): Install
middle compression ring using a piston ring
expander tool. Make sure identi
fi
cation mark is up or
colored dye stripe (if contained) is left of end gap.
Adjust ring gaps.
