Engine Service Manual

79
Disassembly/Inspection and Service
17 690 01 Rev. J KohlerEngines.com
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.
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. Refer to Specifi cations.
5. After installing new compression (top and middle)
rings on piston, check piston-to-ring side clearance.
Refer to Specifi cations. If side clearance is greater
than specifi ed, a new piston must be used.
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
C
D
E
B
A
A 2nd Ring Gap B Bottom Oil Rail Gap
C
Oil Ring Expander
Gap
D Top Oil Rail Gap
E Top Ring Gap
NOTE: Rings must be installed correctly. Install bottom
(oil control) ring fi rst and top compression ring
last.
Use a piston ring expander to install rings.
1. Oil control ring (bottom groove): Install expander and
then rails. Make sure ends of expander are not
overlapped.
2. Middle compression ring (center groove): Install
center 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.
3. Top compression ring (top groove): Install top ring
using a piston ring expander tool. Make sure
identifi cation mark is up or colored dye stripe (if
contained) is to left of end gap.
Crankshaft Inspection and Service
Inspect gear teeth of crankshaft. If teeth are badly worn,
chipped, or some are missing, replacement of crankshaft
will be necessary.
Inspect crankshaft bearing surfaces for scoring,
grooving, etc. Measure running clearance between
crankshaft journals and their respective bearing bores.
Use an inside micrometer or telescoping gauge to
measure inside diameter of both bearing bores in vertical
and horizontal planes. Use an outside micrometer to
measure outside diameter of crankshaft main bearing
journals. Subtract journal diameters from their respective
bore diameters to get running clearances. Check results
against values in Specifi cations and Tolerances. If
running clearances are within specifi cation, and there
is no evidence of scoring, grooving, etc., no further
reconditioning is necessary. If bearing surfaces are worn
or damaged, crankcase and/or closure plate will need to
be replaced.