SINGER 251 User Manual

Tlrm 20549

r:ev. (557)

SERVICE MANUAL

AND

PARTS LIST

FOR

SINGER

MACHINES

OF CLASS 251

SINGLE NEEDLE LOCK STITCH

AUTOMATIC OILING SYSTEM

£275Si?

CAUTION—See that the oil reservoir is filled os instructe.d on page 6 before running the machine, even to test

•A Trade Mark of THE SINGER MANUFACTURING COMPANY

the speed. Special attention is olso called, to the hook lubricating instructions on page 7.

THE SINGER MANUFACTURING COMPANY

Copyright © 1957 by The Singer Manufacturing Company

Printed in U. S. A.

FIG. 2. X-RAY VIEW OF MACHINES OF CLASS 251

(LUBRICATING SYSTEM SHOWN IN SOLID BLACK)

FOREWORD

This book contains complete information covering operation, adjustment,

parts list, attachments and special fittings for Machines of Class 251- Descriptions
and exploded vievYS of all parts assemblies on pages 45 to 194 Inclusive, will be
found helpful when ordering any part of the machine requiring renewal.

DESCRIPTION

Machines of Class 251 produce top quality, straight-line, single-needle, lock stitching in fabrics as fine as

ladies' lingerie or as heavy as mens' overcoating.

General Features

Federal Stitch Type #301.

High Speed (see chart on page 4). Maximum speed

dependent upon nature of work and ability of

operator.

Gear driven, lubricated. Rotary Sewing Hook on

horizontal axis makes two revolutions for each stitch.

Upper gears are spiral-bevel. Lower gears are

hypoid-bevel.

Hook Shaft mounted .160 inch forward of vertical

axis of Needle Bar for improved stitch formation.

Drop Feed guided by mounted journal bearings to

prevent side movement of Feed Dog.

Length of stitch determined by a Push-Button Stitch
Regulator on top of machine arm. Regulator includes
Locking Device to prevent changing of stitch length

during machine operation: (For maximum possible

.stitch length, see chart on page 4). Stitch Length Indi

cations on Machine Pulley are in view of operator.

Automatic Lubricating System (see X-Ray View on
opposite page). Centrifugal Pump delivers oil under
pressure from Reservoir to all principal bearings. Oil
wicks lubricate bearing surfaces in head end of ma
chine and return excess oil to Reservoir. Oil Guard
covers entire path of Take-up Lever.

Oil Flow Window, in direct view of operator, reveals

circulation of oil inside machine arm.

Machine Dimensions: Bed length 18-3/4 inches,

width 7 inches. Space at right of Needle 1 1 inches.

Machine Head is supported by Machine Base and

Oil Reservoir, designed to fit the cutout in table.

Machine Pulley 147016. Outside diameter of belt
groove 2.90 inches for 3/8 inch V-belt. Effective diam
eter for 5/16 inch round leather belt is 2-3/8 inches.

When the machine is in operation, the top of the
machine pulley must always turn over toward the
operator.

Knee Lifter, regularly furnished, is an integral part

of the Machine Base and Reservoir.

SPECIAL CHARACTERISTICS OF

MACHINES OF CLASS 251

MACHINES (CLASS AND VARIETY)

TYPE OF
MATERIAL

MAXIMUM

SPEEDt

(R.P.M.)

MAXIMUM

STITCH
LENGTH

NEEDLE BAR
STROKE
(Inches)

251-1

Light-Weight

5000

7

per inch

1-9/64

251-2 251-3

Medium-Heavy

to Light-Weight

5000 4300

5-1/2

per inch

1-13/64 1-7/16

Heavy to

Light-Weight

5-1/2

per inch

251-3 (HEAVY)

Extra-Heavy to

Light-Weight

4300

5-1/2

per inch

1-7/16

PRESSER BAR

LIFT

(Inch)

NEEDLES:
CLASS
AND
VARIETY

SIZES

RECOM

MENDED

fDependent upon nature of material and ability of operator.

9/32

88 X 9

8, 9,10,11,12,
13, 14, 16,

17, 18, 19,

20, 21 and 22

5/16

16 X 257

8, 9, 10, 11, 12, 13,
14, 16, 17, 18, 19,
20, 21,22, 23 and

24

3/8

16 X 257

8, 9, 10, 11, 12,

13, 14, 16, 17,
18, 19, 20, 21,

22, 23 and 24

7/16

16 X 261

16, 18, 19, 21,

22 and 23

SETTING UP

TABLE

CUT-OUT

Fig. 3. Installation of Machine

on Base

When shipped, the base is held to the machine by

a single bolt through the bottom of the base. Discard

this bolt and plug the hole by inserting from inside

the base, the special cap screw K, Fig. 3, furnished
with the machine.

The base fits into a standard table cut-out, as shown

in Fig. 3 and rests on the four corners without

fastening.

Rasp the edges of the cutout, if necessary, as the

base must slide in without driving and must be located

so that the machine head does not touch the table
when it is placed on the base.

Use shims on the corners, if necessary, to prevent

the base from rocking. The base should also be level

in both directions so that the oil level will be accurately

indicated by the marks in the base.

See that the plunger L, Fig. 3 is in place inside the

base, before putting the machine on the base.

Fig. 4. Installation of Knee

Lifter on Machine Base

The machine head rests on the cork gasket in the

base and is not fastened. The machine hinges must

not support the head except when it is tilted back.

The knee lifter is shipped assembled to the base,

except for the knee plate and lever J, Fig. 4. After

the base is in position, loosen the set screws D and E,

Fig. 4 and slide the shaft forward to the position

shown in Fig. 4. Attach the knee lifter lever J. Set the
stop screw F so that there is only a little play of the

lifter before it starts to lift the presser bar, then hold

the screw and tighten lock nut G. Set the rear stop dog

H to allow the presser bar to be just raised to its limit

but not enough to permit further strain on the knee
lifter parts or to permit the action of the knee lifter

to lift the machine from its base.

CAUTION:—Before starting the machine, it must be

thoroughly oiled, in accordance with the instructions

on page 6.

The maximum speed recommended for Machines

251-4 and 251-2 is 5000 revol utions per minute and

for Machine 251-3, 4300 revolutions per minute ac
cording to the material being sewn and the type of
work being done. (See chart on opposite page.)

SPEED

It is advisable to operate these machines at a more

moderate speed the first few days, after which they

can be operated at maximum speed.

TURN BACK MACHINE

LUBRICATION

NEVER ALLOW
OIL TO FALL
BELOW LOW MARK

Fig. 5. Oil Reservoir

FILL TO

HIGH MARK

Machines of Class 251 have an automatic lubricat

ing system in which oil is circulated by means of a
centrifugal pump from a reservoir in the base. X-Ray
view of machine on page 2 illustrates automatic cir
culation of oil in this machine.

BEFORE STARTING THE MACHINE the oil reservoir

must be filled with "TYPE A" or "TYPE C" OIL, sold
by Singer Sewing Machine Company. "TYPE C" OIL
is used when an oil is desired which will produce a
minimum of stain on fabrics, even after a long period
of storage.

Tip the machine back on its hinges and fill the oil

reservoir as instructed in Fig. 5,

Fig. 6. Oil Flow Window

When in operation, the oil level in the reservoir

should be inspected at least twice a month or as oftei^

as necessary, to keep it from going below the LOW

mark, see Fig. 5, in the reservoir.

CAUTION: Correct lubrication is indicated by a con

tinuous stream of oil passing the oil flow window
while machine is running, as shown in Fig. 6.

Should this oil flow become erratic, STOP the ma

chine and do not run the machine again until the oil

flow has been restored.

At least twice each month check the oil level in the

reservoir.

Never allow oil level to drop below LOW mark,

shown in Fig. 5.

When a machine is NEW or has been idle for several

weeks it is advisable to remove the face plate and oil

the needle bar and take-up bearings. Oil the hook as
sembly by hand and check the oil flow, as instructed
on page 7. The automatic oiling system will function
efficiently, after the first few minutes and continue to

lubricate all bearings.

Oil your bobbin winder occasionally by applying

a few drops of oil to the oil well in bobbin winder,
as shown in Fig. 15, page 12.

See instructions, covering Oil Removing Wick As

sembly, on pages 38 to 41.

ADJUSTMENT OF ROTATING HOOK OIL FLOW REGULATOR

Fig. 7. Oil Flow Regulator in Hook Shaft Bushing

The sewing hook is automatically lubricated. The

flow of oil is controlled by Oil Flow Regulator 140551,

Fig. 7.

The Oil Flow Regulator 140551 is set at the factory

for automatic lubrication of the hook under overage

sewing conditions.

Turn Regulator Thumb Screw (see 140551, Fig. 7)

clockwise to increase the flow of oil to the hook as

indicated by the (-|-) sign under its arrow on the head

of the thumb screw.

HINTS FOR PERFECT OPERATION

If the sewing hook should become excessively warm,

it may be due to an insufficient supply of oil to the

hook (see instructions, above, for adjusting Oil Flow
Regulator).

Keep the oil level in the oil reservoir at the HIGH

mark.

Clean out any lint or other waste around the hook,
around the needle slot in the bobbin case holder
and between the feed rows on the under side of the
throat plate.

Clean out any lint or other foreign matter that may
have collected around oil return passages, particu
larly at oil return hole in rear arm shaft bushing.

Turn Regulator Thumb Screw counterclockwise to

decrease the flow, as indicated by the (~) sign under

its arrow on the head of the thumb screw.

To determine whether the oil is properly flowing

to the hook, withdraw the bed slide and hold a

piece of thin paper under the hook while the machine
runs for ten seconds. There should be a pattern of three
oil sprays on the paper; two light lines on the outside
and one heavier spray in the center. If there is no
trace of oil or an excessive amount of oil on paper,
adjust the Oil Flow Regulator, as instructed above, or

replace the oil filter 143350, Fig. 7, in the head of the
hook shaft, as instructed on page 28.

Always keep the bed slides closed when the ma

chine Is in operation.

Do not run the machine with the presser foot resting

on the feed without some fabric under the presser foot.

Do not run the machine when both bobbin case and
needle are threaded unless there is material under the
presser foot.

Do not try to aid the machine by pulling the fabric

lest you bend the needle. The machine feeds the work

without assistance.

When in operation, the top of the machine pulley

must always turn over toward the operator.

NEVER TOUCH THE STITCH REGULATOR PLUNGER

WHILE THE MACHINE IS RUNNING.

NEEDLES

The size of the needle to be used should be deter

mined by the size of the thread which must pass
freely through the eye of the needle. Rough or uneven
thread, or thread which passes with difficulty through
the eye of the needle, will interfere with the successful

use of the machine. (See chart on page 4 to determine

Size as well as Class and Variety of needle required.)

A bent needle may cause the machine to skip

stitches, or it may make it difficult for the operator to
keep a perfectly even margin. In many cases, a run
off will take place.

A hook or burr on the needle point will result in o

finish that looks blurred and when short stitches are

used (20 to 22 per inch), some materials may be cut.

TO SET THE NEEDLE

Check needles often to make sure that defects are

not present.

Orders for needles must specify the Quantity re

quired, the Size number, also the Class and Variety
numbers, separated by an x.

The following is an example of an intelligible order;

"100 No. 16, 88 X 9 Needles."

The best stitching results will be obtained by using

needles sold by Singer Sewing Machine Company.

The above needles are regularly furnished with
nickel finish but are also available with chromium
finish if so ordered.

Turn the machine pulley over toward the operator

until the needle bar moves to its highest point.

After loosening needle set screw, insert needle UP

into needle bar AS FAR AS IT WILL GO, as instructed
in Fig, 8.

The single continuous groove of the needle MUST

face the left end of the machine, as shown in Fig. 8.

Securely tighten needle set screw.

NOTE: The needle is held in place, in Machines 251-2

and 251-3, by means of a needle clamp, instead of the
set screw in needle bar shown in Fig. 8.

MOVE TO

-^-HIGHEST '

POINT

loosen

SCREW

INSERT
NEEDLE UP
AS FAR AS
POSSIBLE

Fig. 8. Setting the Needle

(Mochine 251-1 )

THREAD

On Machines of Class 251- use only left twist

thread in the needle. Either right or left twist thread
can be used in the bobbin.

To determine the thread twist, hold the thread as

shown in Fig. 9. Then roll the thread over toward you—
if the strands of the thread wind tighter, the thread

is left twist; if the strands unwind or separate, the

thread is right twist.

RELATIVE SIZES OF NEEDLES AND THREAD

The following sizes of needles and thread are recommended according to the class of work:

SIZES

OF

NEEDLES

8 to Shirtings, Sheetings, Calicoes, Muslins, Silks, Dress

14

16

and

17

Goods and all classes of general work with light
and medium weight fabrics.

All kinds of heavy Calicoes, light Woolen Goods,

heavy Silk, Seaming, Stitching, etc.

CLASSES OF WORK

SIZES OF

COTTON, LINEN

OR SILK

60 to 80 Cotton

A and B Silk

40 to 60 Cotton

C Silk

18 Tickings, Upholstery, Woolen Goods, Trousers, Boys' 30 to 40 Cotton

Clothing, Cloaks, etc.

19

and

20 60 to 80 Linen

21 to

24 40 to 60 Linen

Heavy Woolens, Tickings, Bags, Heavy Coats,

Trousers, Heavy Clothing generally.

Bags, Coarse Cloths and Heavy Goods.

D Silk

20 to 30 Cotton

E Silk

1 6 to 20 Cotton

10

UPPER THREADING

Fig. 10. Upper Threading

First, turn the machine pulley over toward the oper
ator until needle is at Its highest point, then pass
the needle thread from the unwinder through the

Fig. 11. Threading the Needle

threading points in the order shown in Figs. 10 and 11.

Draw about two inches of thread through the eye

of the needle with which to start sewing.

1. MOVE

TAKE-UP

TO HIGHEST

POINT

Fig. 12. Preparation

11

TO REMOVE THE BOBBIN

Turn machine pulley over toward operator,

until needle thread take-up lever is at highest
point, as shown in Fig. 12.

Reach beneath bed of machine with left

hand and remove bobbin, as instructed in

Figs. 13 and 14.

NOTE: While latch is kept open, bobbin will

be retained in bobbin case.

To remove bobbin from the bobbin case,

release latch and turn open end of bobbin case
downward. Bobbin will drop out, as shown
in Fig. 14.

2. OPEN

LATCH

3. HOLD LATCH
AND PULL CASE

FROM HOOK

Fig. 13. Removing Bobbin Case from Sevving Hook

4. RELEASE

LATCH \

5. BOBBIN 1

DROPS ▼
OUT

Fig. 14. Removing Bobbin

12

TO WIND THE BOBBIN

See Fig. 15

Fasten bobbin winder to table with its driving pulley

in front of the machine belt, as shown above, so that
bobbin winder driving pulley will make firm contact
with machine belt when thumb latch is pressed down
and pulley will be released from contact with belt
when sufficient thread has been wound upon the
bobbin.

Place bobbin on spindle, pushing it on as far as it

will go and pass thread through threading points, as

shown above.

Wind end of thread around the bobbin a few times.
Press down on thumb latch, pushing driving pulley
over against belt, as shown in Fig. 15. Start machine.

Bobbin winder will stop automatically, when the

amount of thread for which it is regulated is wound

upon the bobbin. For more thread on bobbin, turn

screw L inward; for less thread on bobbin, turn

screw L outward.

When winding a bobbin with fine thread, a light

tension should be used. Adjust the knurled nut

U, Fig. 15, to regulate the tension.

If thread winds unevenly on bobbin, loosen screw T
and move tension bracket Z to the left or right, as
required. Tighten screw T.

Bobbins can be wound while the machine is
stitching.

NOTE; Occasionally apply a few drops of oil to the
oil well, shown in Fig. 15, on top of the bobbin winder
frame.

Hold the bobbin so that the thread will

unwind in the direction shown in Fig. 16.

13

TO THREAD THE BOBBIN CASE

SLOT

NEAR

TOP

Hold the bobbin case as shown In Fig. 16

and place the bobbin into it.

/ \

I

Fig. 16. Placing Bobbin

in Bobbin Case

Pull the thread into the slot 1 and under

the tension spring 2, Fig. 17.

/

Draw the thread into the delivery eye at the

end of the tension spring, as shown in Fig. 18.

3. DRAW
THREAD

Fig. 18. Drawing the Thread

Under the Tension Spring

14

TO REPLACE THE BOBBIN CASE TO PREPARE FOR SEWING

1. REPLACE BOBBIN CASE

ON STUD

V

3. PRESS BACK
UNTIL LATCH CATCHES

GROOVE IN STUD

Fig. 19. Bobbin Case Threaded

and Replaced

After threading, take bobbin case by latch in the

left hand and place bobbin case on center stud of
bobbin case holder, as instructed in Fig. 19. Release

latch. Press bobbin case back until latch catches
groove near end of stud. Allow about two inches of
thread to hang free.

TO PREPARE FOR SEWING

Hold slack end of needle thread loosely and turn
machine pulley over toward you until needle moves
down and up again to its highest point, catching bob

bin thread. Draw up needle thread; bobbin thread

will come up with it through hole in throat plate, as
shown in Fig. 20. Lay both threads back under presser
foot.

Fig. 20. Drawing Up the Bobbin

Thread

TO START SEWING

Place material beneath the presser foot and start

to sew, turning the machine pulley over toward you.

TO REMOVE THE WORK

1. Let the thread take-up lever rest at its highest
point.

2. Raise the presser foot.

3. Draw the work toward the rear until it is clear
of the needle.

4. Cut the threads close to the goods.