Kohler K91 Service Manual page 96

•
Manual starting (rope start or retractable start)
is much easier. Without ACR , manual starting at
full compression would be virtually impossible .
•
E lectric start models can use a starter and bat­
tery size that are practical for the applications in
which these engines are used .
•
ACR eliminates the need for a spark retard/ad­
vance mechanism . A spark retard/advance
mechanism would be required on engines with­
out ACR to prevent " kickback" that occurs when
starting . ACR eliminates this " kickback" making
manual starting safer.
•
The choke control setting is less critical , and in
the event of flooding , excess fuel is blown out
of the lifted exhaust valve and does not hamper
starting .
•
E ngines with ACR start much faster in cold
weather than those without ACR .
•
E ngines with ACR can be started with spark
plugs that are worn or fouled . Engines without
ACR probably could not be started with those
same plugs .
INSPECTION AND S E RVICE
The ACR mechanism is extremely rugged and vir­
tually troublefree . If hard starting is experienced ,
check the exhaust valve for lift as follows :
1 . Check exhaust valve to tappet clearance and
adjust as necessary to specification .
2 .
Remove cylinder head and turn the crankshaft
clockwise by hand and observe the exhaust
valve carefully.
When the piston is approximately 2/3 of the way
up the cylinder during the compression stroke , the
exhaust valve should lift off the seat slightly.
If the exhaust valve does not lift , the ACR spring
may be unhooked or broken . To service the
spring , remove the oil pan and rehook spring or
replace it . The camshaft does not have to be re­
moved .
The flyweights are not serviceable. If they are
stuck or worn excessively, the camshaft must be
replaced .
NOT E : The tab on the flyweights is hardened and
is not adjustable . Do not attempt to bend the tab
- it will break and a new camshaft will be re­
quired .
9 . 2
COM PRESSION TESTING
Because of the ACR mechanism , it is difficult to
obtain an accurate compression reading .
To check the condition of the combustion cham­
ber , and related mechanisms , physical inspection
and a crankcase vacuum test are recommended .
AUTOMATIC COMPRESSION RELEASE
(ACR) CHANGES
New ACR Tabs
Engines with serial no. 9006 1 1 8 and after have
hardened and ground steel ACR tabs on the cam­
shaft assemblies. These new assemblies are
manufactured with improved techniques, which
permanently set the ACR mechanism, making ad­
justments to the mechanism unnecessary and im­
possible.
NOTE : Do not attempt to bend these hardened
steel ACR tabs . These tabs will break if bent .
Procedure For Checking And
Adjusting ACR On Engines Prior To Serial
No. 9006 1 1 8
On engines manufactured before serial no.
9006 1 1 8 the ACR can still be checked and reset
using the procedure described below.
ACR is set according to the amount of valve lift on
the exhaust valve . The correct amount of lift is
established by the height of the lifting tab in rela­
tion to the camshaft . If improper lift is suspected ,
the setting can be checked and adjusted as fol­
lows :
1 . Check valve tappet clearances and adjust as
necessary to specification .
2 . Remove cylinder head and turn the engine
over by hand until you reach BDC of the intake
stroke (intake valve will be closing) .
3 . Mount a dial indicator o n the top of the ex­
haust valve and set at O .
4 . Slowly turn the flywheel clockwise and watch
the dial indicator. When the piston is about 2 /3
of the way up the cylinder, the exhaust valve
should open for ACR . Exhaust valve opening
as indicated on the dial indicator should be
. 03 1 - . 04 2 .
I f the exhaust valve does not open t o t h e specified
amount , adjust the ACR according to STEP 5 .