Kohler Command Pro CV173 Service Manual page 49

Normally, very little wear takes place in piston boss or
piston pin area. If original piston and connecting rod can
be reused after new rings are installed, original pin can
also be reused but new piston pin retainers are required.
Piston pin is included as part of piston assembly – if pin
boss in piston or pin itself is worn or damaged, a new
piston assembly is required.
Ring failure is usually indicated by excessive oil
consumption and blue exhaust smoke. When rings fail,
oil is allowed to enter combustion chamber where it is
burned along with fuel. High oil consumption can also
occur when piston ring end gap is incorrect, because
ring cannot properly conform to cylinder wall under this
condition. Oil control is also lost when ring gaps are not
staggered during installation.
When cylinder temperatures get too high, lacquer and
varnish collect on pistons, causing rings to stick, which
results in rapid wear. A worn ring usually takes on a
shiny or bright appearance.
Scratches on rings and pistons are caused by abrasive
material such as carbon, dirt, or pieces of hard metal.
Detonation damage occurs when a portion of fuel charge
ignites spontaneously from heat and pressure shortly
after ignition. This creates two fl ame fronts, which meet
and explode to create extreme hammering pressures on
a specifi c area of piston. Detonation generally occurs
from using low octane fuels.
Preignition or ignition of fuel charge before timed spark
can cause damage similar to detonation. Preignition
damage is often more severe than detonation damage.
Preignition is caused by a hot spot in combustion
chamber such as glowing carbon deposits, blocked
cooling fi ns, an improperly seated valve, or a wrong
spark plug.
Replacement pistons are available in STD bore size.
Replacement pistons include new piston ring sets and
new piston pins.
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 de-glazed before service ring
sets are used.
2. If cylinder bore does not need re-boring 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 Specifi cations.
5. After installing new compression (top and middle)
rings on piston, check piston-to-ring side clearance.
Compare clearance to Clearance Specifi cations. If
side clearance is greater than specifi ed, a new
piston must be used.
14 690 12 Rev. --
Disassembly/Inspection and Service
Install New Piston Rings
Top Compression
A
C Oil Control Ring
E Expander Ring
Piston Ring Orientation
A Top Oil Rail Gap
Oil Ring Expander
C
E Bottom Oil Rail 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.
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 identifi cation mark is up or
colored dye stripe (if contained) is left of end gap.
Adjust ring gaps.
KohlerEngines.com
A
B
D
E
C
F
Middle Compression
B
Ring
D
F
E
D
C
Top Compression
B
D Compression
Gap
Ring
Top Rail
Bottom Rail
A
B
Ring Gap
Middle
Ring Gap
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