Kohler Courage 3000 Series, Руководство по обслуживанию, Страница: 41 / 56

41
Disassembly/Inspection and Service
18 690 01 Rev. F KohlerEngines.com
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.
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 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 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.
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
specifi 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 diff erence 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
Intermediate
Compression Ring
Gap
B
Top Compression
Ring Gap
C Bottom Oil Rail Gap D
Oil Ring Expander
Gap
E Expander Ring F Bottom Rail
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.