Page 1
Fig. 1
The model 8125 is new. It features rear discharge
with a die cast aluminum housing and is a gear
driven self-propelled mower. Fig.
1.
It is a zone start model with the flywheel brake
system. When the bail is released, both the engine
and blade will stop within the 3-second time limit.
Another feature is an adjustable driven pulley
which controls ground speed. It is located under
the pulley cover.
SAFETY
WARNING:
Disconnect the spark plug lead.
Remove two screws and lift cover off. Fig. 2.
.Fig. 2
With the engine operating at 3200 rpm, the ground
speed can be controlled to operate at 2.4, 2.6, 2.8,
3.0
or 3.2 mph.
MODEL
8125
SERVICING AND REPAIR
CHANGING GROUND SPEED.
Fig.
3
Loosen the nut on the idler pulley bracket which
will release the tension on the belt. Remove the nut
and thick washer from the top of the driven pulley.
When a spacer or spacers are not used, they are
stored on top
of
the pulley under the nut and
washer. Fig. 4.
Fig. 4
SERVICE BULLETIN REFERENCES
20-1
OCTOBER
1984
Page 2
With no spacers between the pulley halves, the
ground speed is 2.4 mph at 3200 rpm. Add
one
spacer
between the pulley halves, the speed in-
creases to 2.6 mph.
Two spacers
2.8 mph.
Three
spacers
3.0 mph.
Four spacers
3.2 mph.
Fig.
5
The lower half of the pulley is keyed to the driven
shaft in the transmission. Fig.
6.
After the ground speed has been selected, assemble the top half of the pulley onto the shaft. Fig.
7.
Fig.
7
Slide the pulley down making sure the two halves
are assembled correctly. Fig. 8.
Fig. 6
Fig. 8
Place the extra spacers on top of the pulley, assem-
ble the washer and nut. Tighten the nut. Fig.
9.
Fig.
9
20-2
SERVICE BULLETIN REFERENCES
OCTOBER
1984
Page 3
Move the idler bracket to apply tension on belt and
tighten idler bracket nut. Fig. 10-A. Belt should
deflect approximately 3/8” with firm finger
pressure. Fig. 10-B. Rotate engine several times to
seat belt in grooves. Recheck belt tension and adjust as necessary.
To
replace the belt, remove the pulley cover.
Loosen the nut on the idler pulley bracket which
will release tension on the belt. Fig. 12.
At this time, the belt can be rolled off the driven
pulley, or you can separate the pulley to remove it.
Fig. 10-A Fig. 10-B
BELT REPLACEMENT PROCEDURES
A special belt is used to drive the transmission. It
was specially designed and manufactured for use
only on this mower.
NOTE:
Use only the belt available from Lawn-Boy
No
other
belt will function properly on this mower.
SAFETY WARNING:
Disconnect the spark plug lead.
Fig. 12
It is necessary to remove the engine when replac-
ing the belt.
Remove the blade nut, blade and collar. Remove
three screws securing muffler and crankshaft sup-
port. Remove muffler. Fig. 13.
Fig. 13
Fig. 11
SERVICE BULLETIN REFERENCES..
20-3
OCTOBER
1984
Page 4
Remove the four bolts that retain the engine to the Install a new exhaust gasket. Fig. 16.
muffler plate. Fig. 14.
NOTE:
Hold the engine while removing these bolts. Don’t
let it drop.
Fig. 16
Place the new belt over the drive pulley and set
engine back onto the muffler plate. Fig. 17.
Fig. 14 Don’t disturb the new exhaust gasket when putting
Lift the engine up and remove the old belt.
Also
remove the old exhaust gasket and dispose
of
it.
the engine in place.
Fig. 17
Fig. 15
Page 5
Block one side of mower up. Fig. 18. Clean the
threads of the engine mounting bolts with LOC Quic
Primer, Part #384884. Apply OMC Ultra Lock, Part
#388517 to the threads of the bolts and assemble
all four into the engine mounting holes.
Fig. 18
Tighten all four engine mounting bolts to 150-190
in. Ibs. (11-15 ft. Ibs.)
Clean the threads of the three muffler screws with
LOC Quic Primer, Part #385884. Apply OMC Ultra
Lock, Part #388517 to the threads.
Assemble the muffler, crankshaft support (flange
down) and start the three screws.
Fig. 20
Slide crankshaft support gauge, Part #609968 over
the crankshaft with the thin wall of gauge going
between the support and crankshaft. Fig. 21.
Fig. 19
SERVICE BULLETIN REFERENCES
OCTOBER
Fig. 21
20-5
1984
Page 6
Tighten all three screws to 142-170 in. Ibs., 12-14
ft. Ibs. Fig. 22.
Fig. 22
Assemble the collar, blade and nut onto crankshaft.
Tighten blade nut to 45-50 ft. Ibs.
NOTE:
If
the blade nut has been on and off four times it
should be replaced.
If
not replaced, apply OMC
Ultra Lock to threads of crankshaft before installing nut.
SAFETY WARNING:
Check the torque of
all
fasteners under the deck.
for tightness. A loose fastener can become a
.thrown object.
Assemble the belt on the drive pulley of the
cranksha’ft. With the idler pulley bracket loose, the
belt should assemble over the driven pulley very
easily. Fig. 24.
Fig. 24
Move the idler pulleys to apply tension on belt. Correct tension will be approximately 3/8” deflection
with firm finger pressure. Fig. 25. Rotate engine
several times to seat belt in grooves. Recheck belt
tension and adjust as necessary.
After completing the belt replacement, start and
run the mower to check operation of the drive
system.
Fig. 25
Fig. 23
20-6
SERVICE
BULLETIN
REFERENCES
OCTOBER
1984
Page 7
Fig.
27
Fig.
29
BULLETIN REFERENCES
OCTOBER
1984
20.7
Page 8
To prevent dirt from entering inside of the wheel,
apply Lawn-Boy “A” grease in the groove of the
wheel cover. Fig. 30.
Fig. 30
Every
50
hours of operation the rear wheel bolts
should be lubricated. Remove and clean the wheel
bolt, liberally oil the bearing and each felt washer
and reassemble. Fig. 31.
The transmission assembly is filled with “A”
grease at the factory and should not require additional lubrication. However,
cant is noted coming from around the seals
if
seepage of the lubri-
or
from
the transmission housing gasket area (Fig. 32-A),
grease can be added through the zerk fitting
located on, the lower side of the transmission. Fig.
32-6.
NOTE:
Do
not put an excessive amount in transmission
because there is a possibility of a pressure buildup resulting in seal failures.
Fig. 32-A Fig. 32-6
Should it be necessary to add lubricant to transmission, watch for an
arm when putting grease in. When movement
upward
movement of the clutch
is
noted, stop the flow of lubricant immediately.
Fig. 33.
Fig. 33
20-8
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OCTOBER
1984
SERVICE BULLETIN REFERENCES
Page 9
FRONT WHEEL MAINTENANCE
It
is
not necessary to lubricate the front wheel
bolts.
For engine, exhaust and blade servicing refer
to
their respective sections in the Manual.
TRANSMISSION SERVICING AND REPAIR
WARNING:
Disconnect the spark plug lead.
Remove the hairpin retainers and detach the handle from the brackets. Lay the handle down over
front
of
mower. Fig. 34.
Remove the driven pulley assembly from the
transmission. Fig. 36.
Fig. 36
Remove the 7/16” nut from long transmission bolt
that retains the clutch cable bracket and spring
assembly to transmission. Lift the bracket, springs
and arm assembly off transmission. Lay to one
side.
Fig. 34
Remove two screws and lift cover off. Fig. 35.
Fig. 37
.Fig. 35
SERVICE BULLETIN REFERENCES
20-9
OCTOBER
1984
Page 10
An
“0”
ring
is
preassembled on the hub of the
clutch arm before final assembly. When removing
the arm from the transmission, the
“0”
ring slides
off into the hole and around the square shaft of the
shift fork. It will have to be removed from the hole.
Fig. 38.
Remove the right rear wheel bolt with a 314” socket.
Fig. 38
To
free the transmission from the housing, remove
the shoulder bolt and nut. Fig.
39.
Fig. 39
Fig. 40
Using a pair of expansion pliers, remove the retain-
ing ring from end of shaft. Fig. 41.
Fig.
41
Page 11
The pinion gear is driven with a spring loaded key
located in the shaft. Before removing the gear, turn
it in both directions. It turns forward freely with a
clicking or ratcheting noise. This noise is created
by the key dropping over the driving shoulder of the
gear. Turn backward and the shoulder of the gear
moves up against the key which provides the selfpropelling. This will be found on both rear wheels.
Fig.
42
When removing the gear from the shaft, be very
careful because the key, being spring loaded, can
pop out and be lost. The spring also can become
lost. Fig.
43.
Fig.
43
Behind the pinion gear is another retaining ring.
Remove it and slide the wheel cover off. Remove
the left wheel, pinion gear and wheel cover. Fig.
44.
SERVICE
BULLETIN
REFERENCES
20-11
OCTOBER
1984
Page 12
Push the bronze bearing and retainers out of the
bracket. Check the bearing surfaces for damage
and wear. Replace
if
necessary.
Also
note the six
lubricating holes in the bracket hub. When grease
flows in, it follows a passage around the hub and
out of each hole into the two holes in the bronze
bearing and lubricates the shaft. Fig. 46.
Carefully pull the transmission and shaft assembly
out of the ‘left hand bracket. Fig. 48.
Fig. 48
Unless there is leakage from around the seals or
gasket, or a failure internally, it will not have to be
disassembled.
Fig. 46
The plastic bearing retainers are in two halves. One
half has a lug or tab that locates in the recess of
the other half. The slots permit lubrication to flow
into the holes of the bronze bearing.
NOTE:
The bearing and plastic retainer assembly may be
installed in bracket hub as removed or reversed.
Either way is correct. Fig. 47.
Fig. 49
1.
Input Shaft
2.
Driveshaft
3.
Trans. Mounting Bolt Hole
4. Control Cable Mounting Bolt
5.
Seals
6. Shift Fork
Fig. 47
20-12
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SERVICE BULLETIN REFERENCES
OCTOBER 1984
Page 13
Remo’ve the input (worm) shaft
assembly.
Fig.
50
1. Packing
2. Input Shaft
&
Bearing
3.
Worm Wheel
4.
“0”
Ring Retainer
5.
Shift Collar
6. Shift Fork
7.
Driver Assembly
8.
Bearing & Seal Assembly Fig. 51
and bearing
Fig. 52
1. Bearing
&
Seal Assembly 10. Driven Plates
(7)
2. Thrust Race (Thin)
11. Driven Sleeve
3. Thrust Bearing
12. Pin
4.
Thrust Race (Thick)
13. Shift Collar
5.
Washer (Worm Wheel) 14. Shift Fork
6. Worm Wheel 15.
“0”
Ring Retainer
7. Snap Ring 16. Transmission Packing
8.
Driver 17. Transmission Gasket
9.
Driver
Plates
SERVICE BULLETIN REFERENCES
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20-13
OCTOBER
1984
Page 14
Wash and clean all parts. Inspect for wear or
damage. Replace any worn or damaged parts.
If
either the worm or worm wheel are worn or
damaged (Fig.
52),
always replace both at same
time. Also,
if
one or more of the driver plates or
driven plates are worn or damaged, replace all
of
them.
Whenever complete disassembly of the transmis-
sion is necessary, replace both packings and
gasket (Fig.
52).
Correct sequence in reassembly of the driver and
driven plates into the housing is very important.
If
reassembled incorrectly, the transmission will not
function properly. There are six driver plates (Ref.
2)
and seven driven plates (Ref.
3,
Fig.
54).
Starting
with
a
driven plate, place it in the housing. Next,
assemble a driver plate, then
a
driven and continue
alternating with every other one being a driver plate
and the last one being a driven plate. Assemble the
driven sleeve (Ref.
4,
Fig.
54)
into the plates, turn-
ing
so
it will go all the way down.
If
it has engaged
all of the driven plates, it will be fully seated.
Fig.
54
Fig.
53
1.
Driver
2.
Driver Plate
3.
Driven Plate
4.
Driven Sleeve
The clutch assembly
will
locate between the pin
hole and snap ring groove in the shaft. Fig.
55.
The
spline end of driver housing will locate next to the
groove with the slotted end
of
the driven sleeve be-
ing positioned over the pin hole.
Fig.
55
20-14
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SERVICE BULLETIN REFERENCES
OCTOBER
1984
Page 15
Holding the clutch assembly
in
your fingers, slide Assemble large spacer washer into recess of worm
it onto shaft. Assemble pin in hole and slide wheel. Fig.
59.
assembly over the pin.
Fig.
56.
Assemble worm wheel onto the spline. Fig.
58.
Fig.
58
SERVICE BULLETIN REFERENCES
20.15
OCTOBER
1984
Page 16
Page 17
Check to be sure the larger spacer washer is in the
recess of the worm wheel. Push both bearings up
against each end of transmission assembly.
Assemble the shift fork in the groove of the collar.
As you place the assembly in the gearcase, guide
the lower end of shift fork into pivot hole. Fig. 66.
Fig. 66
Fill the lower gearcase with Lawn-Boy type “A”
grea’se until it is level with gasket surface. Fig. 68.
Fig. 68
Assemble a new gasket and set cover in place.
Fig. 69.
Assemble the worm into the gearcase, Turn a few
revolutions to check its freedom. Fig. 67.
Fig. 67
NOTE:
Only Lawn-Boy type
in this transmission assembly.
“A”
grease is approved for use
If
another lubricant
is used, it will result in a failure of the transmission.
NOTE:
There are two assembly dowels molded into lower
case which locate in holes of upper case.
Fig. 69
SERVICE BULLETIN REFERENCES
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OCTOBER
20-17
1984
Page 18
Assemble the four short bolts into the housings
with the heads on top. Assemble the long bolt from
the bottom up through the long boss. Assemble the
washer, then the nut on the long bolt but don’t
tighten until last. Fig.
70.
The correct procedure in tightening the four short
bolts and nuts is to use a criss-cross pattern. The
required torque on each nut is
35-45
in. Ibs. To ob-
tain equal tightness, tighten one to
20
in. Ibs., then
cross over
to
the opposite corner and tighten to 20
in. Ibs. Tighten the other one on same side to 20
in. Ibs. and the fourth one the same.
Check the rotation of the shaft in both directions.
If
o.k.,
use the same procedure in tightening all
bolts to
35-45
in. Ibs. Recheck shaft rotation.
Fig. 72.
Fig.
70
Run all four nuts on short bolts up snug against
housing. Fig.
71.
Fig. 72
Slip the shaft into the self-aligning bearing of the
left bracket assembly.
A
twisting motion
will
posi-
tion the transmission into place in the mower hous-
ing. Fig.
13.
Fig.
71
Fig.
73
20-18.:
SERVICE BULLETIN REFERENCES
OCTOBER
1984
Page 19
Align the transmission with the mounting hole in
the mower housing. Insert the shoulder bolt
through the mounting hole, install the washer over
the threads, and assemble to the transmission.
Secure with the nut tightened to 35-45 in. Ibs.
Fig. 74.
Before installing the wheel cover on the shaft,
apply Lawn-Boy type “A” grease in the groove. This
grease stops dirt and debris from entering the gear
area of the wheel. Fig. 76.
Fig. 76
Fig. 74
Assemble the right bracket assembly onto the
shaft. Install three bolts and start the nuts. Tighten
to 142-170 in. Ibs. (12-15 ft. Ibs.)
Fig. 75
Assemble the washer, the retaining ring and the
spacer onto the shaft. Fig. 77.
Fig. 77
Apply Lawn-Boy type “A” grease to the keyseats
in the shaft.
Place the small ratchet spring in hole of the shaft.
Fig.
78
SERVICE BULLETIN REFERENCES
OCTOBER
Fig.
78
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iR
1984
20.19
Page 20
Place the pinion gear drive key in slot. Fig. 79.
Fig. 79
To install the pinion gear, it will be necessary to
push the spring loaded key down while sliding the
gear on. Be sure the key stays in place. Assemble
the second spacer and retaining ring. After the gear
is installed, turn it forward. It should turn freely and
you should hear a “clicking” sound which is the key
moving over and off the drive shoulder. Turn it
backward. The driving shoulder inside the gear
should come against the key and stop the rotation.
If
it doesn’t function as described above you have
assembled it backward. Remove the gear very
carefully to prevent losing the key and spring and
turn the gear end for end and reassemble it. Fig. 80.
Apply a film of Lawn-Boy oil to the wheel bolts. Fig.
81-A. Assemble the wheel and tighten the bolt. Also
apply a generous amount of Lawn-Boy
“A”
grease
in the planetary gear of the wheel. Fig. 81-B.
Fig. 81-A Fig. 81-B
Repeat assembly procedures following Fig. 76
through Fig. 81-B on the left wheel.
Fig. 82
Fig. 80
20-20
SERVICE BULLETIN REFERENCES
OCTOBER
1984
Page 21
Reassemble handle back on the mower. Install the
hairpin clips. Fig.
Fig.
83
83.
Attach both springs to the clutch arm and cable
mounting bracket. Fig.
Fig.
86
86.
Place the
“0”
ring retainer cup on the square shift
fork shaft. The open side must be facing up. Fig.
Fig.
84
Assemble the
arm. Fig.
85.
“0”
ring onto the hub of the clutch
84.
Slide the clutch arm onto the shift fork shaft and
press it into place. It will require effort to push it
down due to the resistance of the
Fig.
87
“0”
ring. Fig.
87.
Fig.
85
SERVICE BULLETIN REFERENCES....
OCTOBER
1984
20.21
Page 22
Assemble the clutch cable bracket on the long bolt
in the transmission. Make sure the edge of bracket
is
seated against transmission housing. Assemble
the nut and tighten to
Fig.
88
35-45
in. Ibs. Fig.
88.
Turn the clutch arm clockwise and hold it while
moving the cable spring in its hole. There should
be no tension on it. The hook of the spring should
be slightly loose when moving it with your fingers.
If
it’s too loose, there will be a
loss
of travel in the
clutch arm. This will cause slippage of the clutch
assembly resulting in a slipping transmission.
If
there is tension on this spring, it will cause
creepage or forward travel of the mower. Fig. 89.
Pulling the cable down, holding it against the up-
per part of the handle, place a tie wrap just above
the joint of the lower handle. Pull it tight. The second tie wrap should be placed approximately half
way down the lower handle. The third tie wrap
should be,
positioned
at the bottom of the lower
handle approximately 2-3 inches from the handle
bracket. Fig.
90.
Fig. 90
It requires two 1/2 open end wrenches to adjust
the clutch. Before making adjustments, move the
control handle back and forth 3 or
4
times and
check the connection of the cable spring on the
arm. If it’s out of adjustment as described (too tight
or loose), adjust the two 1/2” nuts at the upper end
of the cable.
If
the spring is too loose, back the upper nut off and run the lower nut up. Check the
looseness of the spring when doing this. If the
spring is tight, turn the nuts in the opposite direction to loosen. Tighten both nuts and, again, move
the control handle back and forth
3
or 4 times.
Check to determine that the adjustment did not
change. Fig. 91.
Fig. 89
If
the cable has been replaced, install new tie
wraps.
20-22
OCTOBER
Fig. 91
SERVICE BULLETIN REFERENCES
1984
Page 23
To
reassemble pulley, washer and speed control
spacers, refer to Figures
4
through
10-B
Assemble the belt cover. Fig. 92. Start, run and test
the mower
for
engine speed, carburetor ad-
ping time. Engine speed should be
3100-3300
rpm
at high speed and 2400-2600 rpm at low speed. It
should run smooth and even and start within two
pulls. The blade must stop within three seconds.
justments, transmission operation, and blade stop-
Fig. 92
SERVICE BULLETIN REFERENCES.
20.23
OCTOBER
1984
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