Kohler K91 Owner's Manual page 207

Valve Plates Note the difference between the pump and motor valve
plates (Fig.
44).
Ensure the correct valve plate is ordered when
replacing,
as the motor plate will fit in place of the pump plate, but will
not function properly. Scratches in the brass surface of the plate that
can be felt with a fingernail indicate an unserviceable valve plate. The
cylinder block may also be unserviceable in this case.
Charge and Implement Valves Note the location of these valves,
depending on whether the tractor has manual or hydraulic lift (Fig.
61).
Using the appropriate valve parts in the correct hole permits setting up
any
piston-piston unit for either type of lift system.
Charge Pump Refer to the installation of the charge pump (Fig.
49).
With the pump end cap positioned
as shown, note that the dowel pin is
down (nearest the sealing surface of the pump end
cap).
The charge
pump can be put on upside-down, and will fail to function.
Also note that the charge pump needle bearing, Fig.
54,
must protrude
above the housing surface, to hold the valve plate in place. Use care to
prevent accidentally pressing the dowel
pin
into the housing. Be
sure
the valve plate notch is over the dowel pin on assembly, or the valve
plate will be ruined.
Control Shaft/Stub Shaft On
1978
and later transmissions, the longer
control shaft is used on both sides of the pump housing (Fig.
57).
Using a later transmission on an earlier tractor may require cutting a
clearance hole in the tractor's sheet metal for the longer shaft.
Acceleration Valves Original equipment valves are different (Fig.
68)
and must not be exchanged during repair. However, the forward valve
is used
as
the service replacement part for both locations.
If an acceleration valve seems to be malfunctioning, ensure the metering
plug hole is open (Fig.
70).
If clogged, it will prevent the valve from
closing. The hole is extremely small,, and it may take a magnifying glass
to see
it.
Motor Section Note that the webbed section of motor housing must
be "up" (Fig.
74),
or motor will run opposite the intended direction.
Special Assembly Note
Ensure you use retaining parts i n the motor section (Items
23,70,73,74,
Pages
61-62),
to ensure the integrity of the cylinder block
attachment to
the
motor
shaft.
On assembly, make absolutely sure
the
cylinder block is locked securely on the motor shaft. Be sure the notch
in the valve plate is over the dowel pin in the motor end cap.
Supplement
3