BLADE,BLADE HOUSING
UNEVEN CUTTING
To check the blade track:
Uneven cutting can be attributed to a warped
at Same
housing,individualwheelsnotSet
cutting height, incorrect blade tracking, bent
blade o r blade stiffener, or bent crankshaft.
Blades out-of-balance can also cause uneven
cutting.
SAFETY WARNING
WHEN SERVICING BLADE, ALWAYS
DISCONNECTSPARK
PLUGLEAD
TOPREVENT
ACCIDENTALLY
STARTING MOWER.
1. Place the mower on a flat, level surface, making
Blade cuts high on one side low on other,
grass is cut uneven. Warped housings very
seldom occur, check all items above.
sureall wheels are set at the same height.
(The self-propelled mower must have the drive
rollers engaging the tires and be in the drive
position.)
2.Measurethedistancebetweenthelevel
surface and
end of the blade in four
90 degreepositions-front,side,rear,
side.
Zeroto
1/8" low or high from a level
condition at front, rear, side "A" andside
“B” is acceptable.
3.
Shim
spacers No. 602913 (.010), NO.
602914 i(.020) or No. 604563 (.025) can be
used between
the
mower
housing
and
muffler! plate to bring the blade back to
thepropertrack.
A .025 shim.adjusts
the
end, of the blade approximately 1/8".
The blade stiffener and blade must always
be straight and in balance.
Re-tighten'theblade nut to 50 ft. lbs. Replace blade nut if removed o r installed more
than four (4) times.
one
All four wheels must be at the same
height to assure operator of even cut.
INCORRECTBLADETRACKING
Swirl,arc,or
half-moon cuts on smooth
level lawns can be caused by the blade being
too high, or too low on front or rear a r e a of
the housing. Also check UNEVEN CUTTING
above.
The
blade
should
be
tipped
down
no more than 1/8" from a level position at
any place checked.
0 1/8” LOW OR
HIGH (OK)SIDE A
FRONT
o TO 1/8”
LOW OR
HIGH (OK)
OF 1/8” UPINSIDEHOUSINGFRONTANDREAR
AT ALL POINTS EXCEPT FRONT
SIDE B
o TO 1/8” LOW OR
HIGH (OK)
A SAFETY
REQUIREMENT
BEGINNING,
PRIOR
TO
THIS
TIME
STANDARD
BLADE
MUST
NOT
EXTEND
HOUSING.
9-12
1973
MODEL
YEAR.
BELOW
SERVICE BULLETIN REFERENCES
REVISED 1978
BLADE,BLADE HOUSING
MOWER BLADES
The blade should be checked periodically for the following conditions:
A dull blade will cut ragged and
deprive the engine of power.
This is a good blade
Plenty of lift
A blade with no lift will not
discharge grass won’t cut
grass evenly.
will cutvery
Twistedblade
ragged.
ALWAYS REPLACE BLADESTHATAREQUESTIONABLE.VIBRATIONFROM
AN OUT OF BALANCEBLADE OR BENT STIFFENER
CANCAUSE SEVERE ENGINE DAMAGE
OPERATOR FATIGUE.
AND
If excess vibration exists with blade & stiffener balanced
and knowing engine is notdamaged, align blade with the
piston, follow steps listed below.
1. Take the spark plugout
of thecylinder.
2. Loosentheblade,stiffener
on the shaft SO that they
hand.
4. Filemarkthecrankshaft
the blade.
end inline with
and adapter
turn easily by
5. Mount the blade in direction
of file mark
thereafter.
3. With thepiston at thetop of thecylinde.r,
mountthebladeperpendiculartothe
piston (at a 90° angle).
NOTE
“C” and “D”series engines.
6. Always
tightentheblade
nut to 50 ft.
lbs
NOTE: F SERIES ENGINES
PISTON
Excessivevibrationcanbereduced
by aligning the blade parallel
WITH
the piston at top dead center.
DEADCENTER
BLADE
I
90°
Turn file mark and blade90’°
BLADE’
I
9-13
SERVICE BULLETIN REFERENCES
REVISED 1978
BLADE,BLADE HOUSING
A blade collar that was damaged and bent when
being removed from crankshaft should always be
replaced. If not replaced, a vibration in the mower
and a rough, unevenor ragged cutting may result.
KEEPBLADESHARP
AND BALANCED
Always keep blade sharp and properly balanced.Tocheckbalance,placeblade
on
saw as illustrated. Mounting holemustbe
centered on saw. If necessary,grind off
is
heavy end of bladeuntilproperbalance
attained.
SAFETY WARNING
PREVENT
TO
POSSIBLE EYE
INJURY WHENGRINDING,ALWAYS
WEAR PROPER EYE PROTECTION.
SAFETY WARNING
ALWAYS
USE
ORIGINAL
EQUIPMENT REPLACEMENT BLADE TO
INSURE
COMPLIANCE
WITH
SAFETY
SPECIFICATIONS.
WHEN
REINSTALLING BLADE, BE SURE
PARTS ARE REPLACED IN THE
SEQUENCE IN WHICH THEY WERE
REMOVED.
ALWAYS REPLACE
BLADE
WITH
CURVED EDGE U P
(TOWARD HOUSING).
1. Collar
2. Stiffener
3. Washer (20 and 21 inch
models only)
9-14
4. Blade
5. Nut
SERVICE BULLETIN REFERENCES
REVISED 1978
BLADES
Until 1983 the blade cutting assembly illustrated
here’ wasused on Lawn-Boy mowers. A new TRICUT blade with abuilt in stiffener now replaces all
blades on 19”. 20”
and 21” mowers manufactured in
1959 through 1982.The new TRI-CUT blade eliminates theuse of the stiffener and washer. The collar
is still required.
1. collar
2. Stiffener
3. Washer (20and 21 inch
models only)
4. Blade
5. Nut
ZONE AND P0W.ER RESTART
The 19”, 20”
and 21” TRI-CUT Blades are used on
zone and power restart models only.
The collar remainson the crankshaft if it is not bent
or damaged. The twolugs of the collar locate inthe
outside holes of the blade to drive it.
BLADE NUTTORQUE IS 45-50 FT.LBS. ON
ZONE AND POWER RESTART MODELS.
BBC MODELS ONLY
BBC TRI-CUT BLADE
Only one TRI-CUT blade
is used onthe blade brake,
clutch model mowers. Thedistance between the outside holesis greater and will not fit other models with
the collar.
BLADE BOLT TORQUE ON BBC MODELS IS
28-31FT. LBS.
SERVICE BULLETIN REFERENCES.
.9-15
REVISED 1983
,BLADE,BLADE HOUSING
BROKEN OR CRACKED HOUSING
Housing breakage is nevercovered under
flaw
is
warranty except when a definite
found in the metal. However, broken housings can be welded.
NOTE
For welding of the aluminum or magnesium housings, an experiencedwelder is
recommended.
A Heliarc Welder using alternating current (AC) will weld both aluminum and
magnesiumhousings.
I
NOTE
I
Do not attempt to weld these housings in
the Direct Current (DC) mode.
To Weld Aluminum Housings
Use the Heliarc Welderin AC mode with 40-43 aluminum roil.
To Weld Magnesium
Housings
Use the Heliarc Welder in AC mode with pure
magnesium rod.
SAFETY WARNING
WELDING MAGNESIUM HOUSINGS
WITH AN ACETYLENE TORCH IS
NOT RECOMMENDED. A POSSIBILITY OF A FIRE AND/OR AN EXPLOSION WILL EXIST.
NOTE
Allmagnesium decks have the word
"MAGNESIUM" cast-inplace on the
left side near "PLACEFOOT HERE
WHEN STARTING."
9-16.
.SERVICE BULLETIN REFERENCES
TROUBLE SHOOTING
BLADE, BLADE HOUSING
COMPLAINT
CAUSE
Blade dull, nicked, out of balance
X
Blade bent
X
Weak blade stiffener
X
Blade fastener loose
X
Unequal wheel heights
X
Mower housing bent or warped
X
Muffler plate warped/not straight
X
Bladel/Spacerwasher missing (20 & 21” only)
Insufficient engine speed
Insufficient blade tip speed
Cutting wet grass
Grass too long
Rough & uneven turf
X
Forward travel too fast for cutting conditions
Erratic mowing habits
a. Fast and slow movements of
mower (jerky operation)
b. Bouncing of handle, etc.
SERVICE BULLETIN REFERENCES..
X
X
9-17
ROTARY MOWER BLADE TIP SPEED
21” BLADE
RPM
19” BLADE
Ft. Per
Min
Miles
Per
Hour
3487
18,997
3400
210
18,523
*3300
204
17,978
*3200
198
17,434
*3100
191
18” BLADE
Ft. Min
M.P.H.
Per
215
Ft. Per Min
M.P.H.
195 17,299
189
16,799
180
16,305
185
i75 15,378
180
15,811
168 14,912
16,889
174
15,317
164
14,446
185
3000
16,344
168
14,823
159
13,980
2900
179
15,799
163
14,329
2800
173
15,254
157
13,835
167
2700
14,710
152
13,341
*2600
160
14,165
146
12,847
138
12,116
*2500
154
13,620
140
53
12,3
**11,650
132
*2400
148
13,075
133 **11,858
**11,184
127
15,844
*Minimum & Maximum Speeds Recommended For Operation Of Lawn-Boy Mowers
**NOTE: Blade Tip Speed Below 12,000F.P.M. Will Not Bag Grass Satisfactorily
SAFETY WARNING:
TO MINIMIZE THE HAZARDPOTENTIALOFPOSSIBLEFOREIGN,
OBJECTSSTRUCKBYTHECUTTINGBLADE,BLADE
TIP SPEED
SHOULD NEVER EXCEED19,000 FEET PER MINUTE
FEDERALSAFETYSTANDARDSDOESNOTPERMITBLADE
SPEED TO EXCEED 19ooo FEET PER MINUTE.
9-18
SAFETY RELATED.
TIP
.SERVICE BULLETIN REFERENCES