Kohler K91 Service Manual page 111

PISTON AND RINGS
Identification
Three different styles of pistons are cu rrently being
used in Kohler K-Series engines.
Style pistons
" A" can be used in all K-Series en­
gines . The style A piston can be identified by its
full skirt and its lack of an installation direction
identifier on its crown (a new piston can be in­
stalled facing either direction) .
No I nstallation
Difection IdeA, t if,ie,r
The Style piston
" e"
is used on the K34 1 engines
only. It can be identified by its partial skirt and
raised criss-cross design in the recessed area
around the piston pin bore . In additio n , it has an
installation direction identifier (a notch) at its top .
The style C piston is to be installed with the notch
facing the flywheel .
Installation
Direction
Identifier
(Notch)
Style C Piston
The Style piston
II on
has been used on the K1 8 1 ,
K30 1 , and K32 1 engines. It can be identified by its
partial skirt and rectangular recessed area around
the piston pin bore . In additio n , it has an installa­
tion direction identifier, Fly, which is stamped into
the top of the piston. The style D piston is to be
installed with the arrow of the Fly mark pointing
towards the flywheel .
1 1 . 8
factory. Cylinder blocks are honed to the Standard
sponding pistons . Blocks using the oversize are
are used in these blocks to prevent possible fail­
ure such as a noisy engine or eventual piston skirt
cracking. These pistons are available from Kohler.
Standard Service Rings should be used with both
Standard and . 003 " oversize pistons . Ring end
gap will increase slightly when installed on . 003 "
oversize pistons; however, sealing is maintained
due to the ring desig n .
Inspection
Scuffing and scoring of piston and cylinder wall
occur when internal temperatures approach the
melting point of the piston . Temperatures high
enough to do this are created by friction , which is
usually attributed to i mproper l ubrication , and/or
Partial Skirt
overheating of the engine.
with Raised
Normally, very little wear takes place i n the piston
boss-piston pin area . If the original piston and
connecting rod can be reused after new rings are
installed , the original pin can also be reused but
new piston pin retainers are required . The piston
pin is included as part of the piston assembly - if
the pin boss in piston , or the 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 . oif is allowed to enter the combustion chamber
where it is burned along with the fuel . High oil
consumption can also occur when the piston ring
end gap is incorrect because the ring cannot
properly conform to the cylinder wall under this
condition . Oil control is also lost when ring gaps
are not staggered d uring installation .
When cylinder temperatures get too hig h , lacquer
and varnish collect on piston causing rings to stick
which results in rapid wear . A worn ring usually
I nstallation
Direction
Ide. n tl,fier
Style 0 Piston
Piston Sizes - All Styles
In order to ensure a correct fit between piston and
cylinder we utilize two cylinder bore sizes at the
(STD) size or . 003 : ( .075mm) oversize with corre­
stamped on the cylinder head gasket surface with
. 003 " . It is essential that . 003 " oversize pistons
Partial Skirt