Singer 451k51 Troubleshooting guide

Form K6518
(1266)
SERVICE MANUAL
PARTS LIST
SINGER
451k51
HIGH SPEED
LOCK STITCH
SINGLE NEEDLE
VERTICAL TRIMMER
MACHINE
Machine 451K51
THE SINGER COMPANY
Copyright Under International Copyright Union
•A Trademork of THE SINGER COMPANY
Printed In Greot Britain
From the library of: Superior Sewing Machine & Supply LLC

CONTENTS
Page
DESCRIPTION 3
SETTING UP 4
LUBRICATION 5. 6
INFORMATION FOR OPERATOR 7-14
Page
TIMING AND ADJUSTING 15-22
REMOVAL AND REPLACEMENT OF
PRINCIPAL ASSEMBLIES 23-26
PARTS CHART 28, 29
PARTS LIST 30,31
INDEX
Alignment
Arm Shaft with Hook Driving Shaft
Arm Shaft 15i 25, 26
Arm Shaft Connection Belt 3, 25
Arm Shaft Connection Belt Pulley 25, 26
Automatic Lubrication 6
Ball Bearings and Needle Bearings 15, 25, 26
Bobbin 7
Bobbin Case 8-10,14
Bobbin Case Holder 16, 18, 23
Bobbin Case Holder Needle Guard 16, 18
Bobbin Case Slide
Bobbin Thread 7, 9
Bobbin Thread Tension 10
Bobbin Winder 5» 8
Broken Thread 7, 12
Carefree Operation Hints 14
Centralisation of Feed Dog 21
Change of Stitch Length 11,22
Check-Spring 18, 19
Cleaning 5, 12, 20, 24
Connection Belt, Arm Shaft 3, 25
Common Causes of Stitching Troubles 7
Cover Guard (Take-up) 12, 16
Daily Care 5
Damaged Needles 7
Damaged Parts 14
Dimensions of Machine 3
Drawing Up Bobbin Thread 9
Drip Pan, Installation 4
Face Plate, Removal and Replacement 19
Feed Dog 15, 21, 22
Feed Driving Eccentric Gib 22
Feed Driving and Reversing Mechanism 22
Feed Driving Eccentric 22
Feed Driving Eccentric Adjusting Disc 22
Feed Mechanism (Pendant Link) 3, 16, 21, 22
Feed Movement, Description 21
Feed Reversing Lever Stop Pin 22
Formation of Stitch 10
Fraying of Material 7
Gib
(Feed Driving Eccentric) 22
Hints for Carefree Operation 14
Hook
Clearance to Needle 17
Description 3
Lubrication 6
Removal and Replacement 23
Stringing • 18
Timing 17
Hook Driving Shaft 15, 25
Hook Oil Shield, Installation 6
Hook Oil Wick 6
Hook Section 23
Knee Lifter 3, 4, 14
Knee Lifter Rod Spring 22
Knives
Aligning Upper Knife to Lower Knife 13
Eliminating Side Movement of Knife (Upper)
Holder Bracket 13
Replacing Knives 14
Setting, Lower and Upper Knives to
Correct Height 13
Length of Stitch 3, 11, 22
Light Fixture Mounting Seat 3
Page
15
Page
Locking Feed Driving Eccentric 22
Loop Lift 15
Machine Pulley 3, 5, 14, 25
Machine Rest Pin 4, 14
Machine Storage 5
Needle 7
Needle Bar and Bushing 15-17, 26
Needle Bar Connection Link 26
Needle Bar to Presser Foot, Clearance and
Alignment 20
Needle Bearings 3, 15
Needle Beakage, Prevention 7, 14, 18
Needle to Hook Clearance 17
Needle Guard 16, 18
Needle Threading 7
Needle Thread Tension 10, 18, 19
Needle Thread Tension Releaser 10, 20
Oil Reservoir 3, 5, 25
Oil Shield (Hook) 6
Oil
Wick ( Hook) 6
Pendant Link Feed Mechanism 3
Perfect Stitch 10
Position Finger 6, 17
Preliminary Inspection 15
Preparation for Sewing 9
Presser Bar and Bushing 20
Presser Foot 11, 14, 15, 19, 20
Pressure of Presser Foot 11,22
Prevention of Unauthorised Change of
Stitch Length 22
Puckering 21
Pulley
(Arm Shaft Connection Belt) 25, 26
Pulley, Machine - 3, 5, 14, 25
Removing Broken Thread 12
Rest Pin 4, 14
Reverse Feed 3, 11, 19, 22
Reversing Lever Stop Pin 22
Rock Shafts 24
Rotary Take-up (See "Take-up")
Sewing Hook (See "Hook")
Speed 3, 14
Setting the Needle 7
Specifications 15
Spillage of Bobbin Thread 8
Starting to Sew 12
Stitch Formation 10
Stitch Length 3, 11, 22
Stitch
Regulator 8, 11
Stitching Troubles, Causes 7
Stringing the Needle Guard (Hook) 18
Superfmish 14
Tacking 3, 11,19
Take-up.... 3, 15, 19
Take-up Cover Guard 12,. 16
Tension Devices 3
Tension Releaser (Needle Thread) 20
Threading 7, 9
Thread Beakage 7, 12
Thread Cutters 3, 12
Thread Tensions 10, 19
Trimmer
Adjusting 12
Changing Trimming Margin 12
Disengaging 12
Turning a Corner 12
V-Belt 3
Wearing Checks 6, 15, 20, 21
Winding the Bobbin 8
From the library of: Superior Sewing Machine & Supply LLC

DESCRIPTION
Machine 451 K51, for stitching and trimming
light and medium weight fabrics.
Lock stitch (Stitch Type #301)
Single needle, Catalogue 1361 (88x9)
Socket-type needle bar
Short arm, flat bed
Drop feed. Pendant link feeding mechanism
with reinforced feed bar insures level feed motion
and uniform stitch length at all speeds.
• Reverse feed, hand operated, with spring
return to forward stitch. Performs precise tack
ing and strong seam reinforcing with minimum
thread breakage.
• Maximum stitch length, 6 to the inch
forward and 7 to the inch in reverse.
Vertical Trimmer. Trims 1/8 to 5/16 inch to
the right of seam as desired.
Special fittings for trimming 3/32 inch from
the line of stitching can be furnished if specified
on order. Unless otherwise ordered machine
will be fitted to trim 1/8 inch to right of seam.
The upper knife may be thrown out of action at
will for straight stitching. Upper knife stroke
9/64 inch.
Modified, single rotary take-up maintains
constant thread control to meet hook require
ments. Easy to thread. Simple to adjust.
Long point rotary sewing hook on horizontal
axis (belt driven); automatic lubrication can be
regulated.
One oil reservoir and three easily accessible oil
holes serve all principal bearings in machine.
Rotary tension and pre-tension devices achieve
precise thread control throughout speed range of
stitching with all types of natural and synthetic
threads and materials of light and medium
weight—permitting lightest tensions for perfect
"wash and wear" sewing.
Tension guard, mounted on face plate, protects
rotary tension from broken threads, lint and
other hazards.
Two thread cutters; One, on face plate, pre
vents wrapping of broken thread around rotary
take-up. The other, on rear of thread guard,
removes excess broken thread from take-up.
Durable, steel - reinforced, rubber driving belt
270926, from arm shaft to hook driving shaft, is
readily accessible when rear arm cover is re
moved.
Large rim, aluminium machine pulley 276445,
for 3/8 inch V-belt, is designed for safety. Out
side diameter of belt groove, 2.9 inches. Effective
diameter for 5/16 inch round leather belt, 2-3/8
inches.
Tapped hole and seat in rear of arm provided
for mounting a light fixture.
Compact stitch length mechanism is easy to
read and to set.
Enclosed knee lifter rod and connection to
knee lifter 228710.
Needle bar stroke, 1-9/64 (1.140) inches.
Presser bar lift (capacity of machine), 9/32
(.281) inch.
Bed dirnensions: Length, 15-11/16 inches.
Width 7 inches. Working space at right of
needle, 8 inches.
Double shielded ball bearings at both ends of
arm shaft and at pulley end of hook driving shaft.
Needle bearings for feed driving and feed lifting
connections and for needle bar connecting link.
Nylon insert bearings for feed driving rock
shaft and feed lifting rock shaft.
Controlled pressure lubricated bearings on
hook shaft.
TOP OF MACHINE PULLEY TURNS OVER
FROM THE OPERATOR.
CAUTION
Do not start machine until it has been thor
oughly oiled, as instructed on pages 4, 5 and 6.
SPEED
Maximum speed recommended is 5000 stitches
per minute, with these exceptions . . .
• Run a new machine at a more moderate
speed the first few days.
• A machine that has been idle, for a long
period of time, should be run slower than maxi
mum speed for the first few minutes to allow
time for oil to reach the moving parts. Check
principal bearing points for freedom of move
ment and adequate lubrication before running
machine at top speed.
• Reduce speed of machine when sewing
closeiy woven or treated material.
Maximum efficient speed is dependent upon ,
the nature of the operation, the ability of the
operator and the type of thread and material in
use.
Never force machine beyond its maximum
efficient speed for the work being accomplished.
Disregard of this precaution could result in con
siderable damage to machine.
From the library of: Superior Sewing Machine & Supply LLC

SETTING UP
DRIP PAN
Position drip pan on underside of table, as shown
in Fig. 2, with its right end even with right inside
edge of machine cut-out in table.
Using four 3/4 inch wire nails, fasten drip pan low
enough in table cut-out to avoid interference with
rock lever rod (shown in Fig. 2).
KNEE LIFTER
Using three 7/8 inch wood screws (shown at 1,
Fig. 2)
fasten rock lever bracket 2 to underside of
table. Locate bracket 2 so that rock lever rod can rise
and fall through hole provided for it in drip pan with
out striking edge of hole.
Locate rock lever extension 3 to hold rock lever rod
equidistant from front and rear edges of hole in drip
pan. Make certain that platform at top end of rod
will be directly under knee lifting rod A, ^g. 5, page 5,
in machine; then securely tighten clamp screw 4.
Raise rock
lever rod 5 to bring Its platform just
below knee lifting rod in machine, when at rest. Make
certoin platform is turned as shown in Fig. 2 and se
curely tighten clamping screw 6.
Knee plate 7 may be raised, lowered or turned to
suit the requirements of the operator, after loosening
clamping screw 8. Knee plate arm 9 may also be
moved toward the left or right and toward front or
rear, as required after loosening clamping screw 10.
Tighten both screws 8 and 10 securely when correct
position is obtained.
Set stop stud 11 to stop the action of the knee lifter
as soon as knee lifter raises presser foot high enough
to trip hand lifter on machine. Securely tighten clamp
ing screw 12.
MACHINE HEAD
Machine head should rest upon cushioning pads in
four corners of cut-out in table. Machine is not fas
tened. Machine hinges must not be required to support
head except when machine is tilted back upon ma
chine rest pin on table.
BELT GUARD
NOTE: Belt Guard 106505 is supplied with
the machine only when requested on order.
Remove arm side cover screw and fit belt
guard bracket 1, Fig. 3 with long hinge screw 2.
Insert belt guard support 3, Into bracket 1, and
belt guard 4, as illustrated. Adjust belt guard
so that It just clears the machine pulley, then
tighten the Allen screws in the bracket and belt
guard with the special key.
FRONT EDGE OF TABLE
PLATFORM
ROCK LEVER ROD—
Fig. 2. Drip Pan and Kne« Lifter
beneath the Table
•>;
Fig. 3. Belt Guard In Position
I ^
'f I
i# ;
From the library of: Superior Sewing Machine & Supply LLC

OIL
FILL OIL reservoir:
OIL SHOULD SHOW
AT HIGH MARK —
DIRECTION
OF
ROTATION
NEVER AlToW oil
O FALL BELOW LOW
MARK ON* GAUGE
OIL
OIL
Fig. 4. Oil Reservoir and other
Oiling Points on Machine
Fig. 5. Priming Points beneath
Machine Bed
Fig. 6. Bobbin Winder Lubrication
MACHINE PULLEY
When machine Is In operation, machine pulley
always must turn over away from the operator,
as shown in Fig. 4.
CAUTION: Do not start the machine, not
even to test the speed, until it has been thoroughly
oiled as instructed below.
LUBRICATION AND CLEANING
Use SINGER* OIL 'TYPE A" or "TYPE C". See inside
front cover of this book for description of these oils.
Keep machine clean end well oiled at oil times.
OIL RESERVOIR
Fill by lifting out oil gouge and applying oil to hole
in machine bed, as instructed in Fig. 4. Reservoir sup
plies oil to sewing hook race, to eccentrics and to
front bushing on hook driving shaft.
DAILY CARE
Apply a few drops.of oil to the four oil holes
shown In Fig. 4.
Check oil level in reservoir before starting machine.
Add oil, when necessary to maintain level at HIGH
mark. Never allow oil level to drop below lower mark
on gauge.
Occasionally remove the cover for the trimmer
driving crank and apply oil to the oiling points
shown in the insert Fig. 4. Always clean the
cover before replacing it.
AFTER INSTALLATION
New machines and machines installed after several
weeks of idleness should be primed before using.
Residual lubricant
may have congealed or disappeared
entirely.
Apply a few drops of oil to priming points shown
in Fig. 5, beneath machine bed.
Oil hook assembly by hand. Check oil flow
and adjust when necessary, as instructed below
and on page 6. Proceed with "DAILY CARE"
as instructed above.
BOBBIN WINDER
Apply a few drops of oil daily, or more often when
necessary, to oil wick in bobbin winder frame as in
dicated in Fig. 6.
CLEANING
Remove all lint and abrasive matter from around
hook and from between feed rows on underside of
throat plate.
Remove dirt from clean-out hole C, Fig. 4 in needle
bar, pushing shank of a needle through hole. Wipe
off all excess oil from
areas of machine that may
come in contact with material to be sewn.
Machines not in use should be kept well oiled, clean,
dry and covered.
From the library of: Superior Sewing Machine & Supply LLC