Piston Style B; Install New Piston Rings; Piston Style A - Kohler Courage SV710 Service Manual

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.
Pre-ignition or ignition of fuel charge before timed spark
can cause damage similar to detonation. Pre-ignition
damage is often more severe than detonation damage.
Pre-ignition 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:

Piston Style A

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. Top and center
compression ring end gap clearance is 0.25/0.56
mm (0.0100/0.0224 in.) for a new bore, or 0.94 mm
(0.037 in.) for a used bore.
5. After installing new compression (top and middle)
rings on piston, make sure top compression ring-to-
groove side clearance is 0.025/0.048 mm
(0.0010/0.0019 in.) and middle compression ring-to-
groove side clearance 0.015/0.037 mm
(0.0006/0.0015 in.). If side clearance is greater than
specifi ed, a new piston must be used.
32 690 01 Rev. G
Disassembly/Inspection and Service

Piston Style B

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. Top compression ring end
gap clearance is 0.189/0.277 mm (0.0074/0.0109
in.) for a new bore, or 0.531 mm (0.0209 in.) for a
used bore. Center compression ring end cap is
1.519/1.797 mm (0.0598/10.0708 in.) for a new bore,
or 2.051 mm (0.0808 in.) for a used bore.
5. After installing new compression (top and middle)
rings on piston, make sure top compression ring-to-
groove side clearance and is 0.030/0.070 mm
(0.0010/0.0026 in.) and middle compression ring-to-
groove side clearance 0.030/0.070 mm
(0.0010/0.026 in.). If side clearance is greater than
specifi ed, a new piston must be used.

Install New Piston Rings

NOTE: Rings must be installed correctly. Ring
installation instructions are usually included with
new ring sets. Follow instructions carefully. Use
a piston ring expander to install rings. Install
bottom (oil control) ring fi rst and top
compression ring last.
To install new piston rings, proceed as follows:
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 to 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 left of end gap.
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