Kohler K91 Service Manual page 22

9 . Low compressio n .
E n g i n e Uses Excessive Amount o f O i l
I ncorrect oil viscosity or type .
1 .
2 . Clogged o r improperly assembled breather
system .
3. Worn o r broken piston rings .
4 . Worn cylinder bore .
5 . Worn valve stems and/or guides.
EXTERNAL E N G I N E INSPECTION
o
Before cleaning or disassembling the engine,
check its external appearance and condition .
This inspection can g ive clues to what might
be fou nd inside the engine (and the cause)
once it is disassembled .
o
Check for build u p of dirt and debris on the
crankcase, cooling fins, grass screen and
other external surfaces . Dirt or debris in these
areas are causes of overheating.
D
Check for obvious fuel and oil leaks and dam­
aged components . Excessive oil leakage can
i ndicate a clogged or i mproperly assembled
breather, worn or damaged seals and gaskets
or loose or improperly torqued fasteners .
D
Check the air cleaner cover, element cover
and air cleaner base for damage or indications
of improper fit or seal .
o
Check the air cleaner element . Look for holes,
tears, cracked or damaged sealing surfaces or
other damage that could allow dirt to enter the
engin e . Also note if the element is clogged or
restricted. These conditions could indicate that
the air cleaner has been underserviced .
o Check the carburetor throat for dirt . Dirt in the
throat is further indication that the air cleaner
is not functioning properly.
o
Check the oil level . Note if the oil level is
within the operating range on the dipstick, or if
it is low or overfilled .
o
Check the condition of the oil . Drain the oil
into a container - it should flow freely. Check
for metal chips and other foreign particles.
NOTE : It is good practice to drain oil at a location
away from the workbenc h . Be sure to allow ample
time for complete drainage .
Sludge is a natural by-product of combustion ; a
small accumu. l ation is normal. Excessive sludge
formation could indicate that the oil has not been
changed as recommended, an incorrect type or
weight of oil has been used , over-rich carburetor
setti ngs or weak ignition, to name a few .
4.2
C LEANING THE E N G I N E
After inspecting t h e external condition o f t h e e n ­
gine, clean it thoroughly before disassembling .
Also clean individual components as the engine is
disassembled . Only clean parts can be accurately
i nspected and gauged for w ear or damag e .
There are many commercially available cleaners
that q uickly remove grease, oil and grime from
engine parts . When such a cleaner is used, follow
the manufacturer's instructions carefully. Make
sure all traces of the cleaner are removed before
the engine is reassembled and placed in opera­
tio n . Even small a mounts of these cleaners quickly
break down the lubricating properties of engine oil .
BASIC E N G I N E TESTS
Fuel System Test
To determine if fuel is getting to the carburetor,
disconnect the fuel line at inlet to carburetor - if
fuel does not flow out of line, check system back
to tank for clogged lines, wrong (unvented) filler
cap, blocked filter screen, faulty fuel pump, etc . If
fuel is getting as far as the carburetor, remove
the spark plug , crank engine and check for fuel
inside combustion chamber. If n o fuel is present
here , check for faulty carburetor.
Ignition System Test
To determine if the ignition system is good, re­
move the spark plug and place plug with side
electrode against cylinder head then crank engine
at sufficient speed to produce a good spark. If a
sharp, snappy spark is noted, this eliminates the
ignition system components as the cause, al­
though the ignition timing could be off .
If no spark or a weak spark is produced , check
the ignition system further. If points are pitted,
don't attempt to service them - replace points in
bad shap e . Dirty points may be cleaned . A bad
condenser will cause premature failure of pOints .
Check the breaker p ush rod for evidence of bind­
ing or sticking - replace as needed . Condenser
can be tested on commercial tester per tester
manufacturer's instructions. Check ignition coil on
coil tester for continuity.
Crankcase Vacuum
A partial vacuum should exist in the crankcase
when the engine is operating at normal tempera­
tures . Pressure in the crankcase (usually caused
by a clog ged or i mproperly assembled breather)
can cause oil to be forced out at oil seals, gas­
kets or other available spots.
Crankcase vacuum is best measu red with a slack
tube manometer . The manometer included in the