Service and Repairs

85
Disassembly/Inspection and Service
17 690 01 Rev. L KohlerEngines.com
Dimension C
C
Camshaft Journal Specifi cations
Engine Model Dimension C Limit
CH245, CH255
13.975 mm
(0.5500 in.)
13.966 mm
(0.5498 in.)
CH260, CH270
13.975 mm
(0.5500 in.)
13.900 mm
(0.5470 in.)
CH395, CH440
15.975 mm
(0.6289 in.)
15.900 mm
(0.6260 in.)
Inspect gear teeth of camshaft. If teeth are badly
worn, chipped, or some are missing, replacement of
camshaft will be necessary. If unusual wear or damage
is evident on either lobe or mating tappet, camshaft and
both tappets must be replaced. Check condition and
operation of ACR mechanism.
Measure cam lobe profi le, A and B, using an outside
micrometer and compare with specifi cations listed.
Measure camshaft journals, C, which fi t in ball
bearings, for wear using a micrometer. Compare with
specifi cations listed.
Remove Piston, Connecting Rod and Crankshaft
NOTE: If a carbon ridge is present at top of cylinder
bore, use a ridge reamer to remove it before
attempting to remove piston.
1. Remove screws securing end cap to connecting rod.
Remove end cap. Carefully guiding connecting rod,
slide piston and connecting rod from cylinder bore.
2. Remove crankshaft from crankcase.
Connecting Rods Inspection and Service
Check bearing area (big end) for excessive wear, score
marks, running and side clearances (see Specifi cations
and Tolerances). Replace rod and cap if scored or
excessively worn.
Service replacement connecting rods are available
in STD size and 0.25 mm (0.010 in.) undersize. 0.25
mm (0.010 in.) undersized rods have an identifi cation
marking on lower end of rod shank. Always refer
to appropriate parts information to ensure correct
replacements are used.
Piston and Rings Inspection
Scuffi ng and scoring of pistons and cylinder walls occurs
when internal engine temperatures approach welding
point of piston. Temperatures high enough to do this are
created by friction, which is usually attributed to improper
lubrication and/or overheating of engine.
Normally, very little wear takes place in piston boss-
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 are 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 2 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 wrong spark
plug(s).
Replacement pistons are available in STD bore size,
and 0.25 mm (0.010 in.) oversize. Replacement pistons
include new piston ring sets and new piston pins.
Replacement ring sets are also available separately for
STD, and 0.25 mm (0.010 in.) oversize 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.