Singer 620 User manual

SINGER
CLASSES 620, 625, 626 AND 628

Supplement to
Form 20732 .
Machines 620, 625, 626 and 628
' (1066)
SINGER
SERVICE MANUAL
MACHINES OF CLASSES
620, 625, 626 AND 628
Instructions appearing in the Service Manual for Machines of Class 600 generally apply to
Machines of Classes 620, 625 and 626. Instructions for Class 603 Machines generally apply to
those of Class 628. This supplement provides instructions which apply only to Class 620 625
626 and 628 Machi nes.
THE SINCER COMPANY
* A Trademark of THE SINGER COMPANY
Insert in Form 20732, Swing Needle Service Manual
Printed in U. S. A,

INDEX
Bobbin Driver
Adjustment....
Removal and Replacement..—.
Bobbin Push-Button
Removal and Replacement__—.---
Chainstitch Adjustments.........
Hinge Assembly...-.
Hoolc, Rotating
Positioning...-.
Removal.
Replacing...-.
Timing...
Inspection and Lubrication...—.....
Needle-Threader Storage and Use...
Selector Systems
Release Mechanism.. . ....—-
The Cam Stack...-.-
Bight-Amplitude and Pattern Selector.
Needle-Bar Driving Arm.
Tension, Needle Thread
Adjustment.
Removal and Disassembly.
Reassembly and Reolacement.
Throat-Plate Position Bracket
Remove i ana R ss icc oment.
Winding Mechanism.
•Viring Dicgram.
9
9
9
20
5
8
6
6
7
3
22
12
14
17
19
10
10
10
PROPERTY OF
THE SINGER COMPANY
This is a private and confidential communication to and for the use only
of the employees of The Singer Company and its affiliated companies.
Reproduction, sale, distribution, or publication thereof to the public is
forbidden.
2

INSPECTION AND LUBRICATION
Before any extensive inspection is undertaken to
find causes of faulty operation, the machine should
be thoroughly cleaned and lubricated.
Remove lint, fluff, dust or other foreign particles
from the hook, feed dog, and bobbin case.
Remove bobbin case and clean in varsol. Open
face plate and clean out lint or waste collected
around needle bar, presser bar, and pressure regulator.
CLASS 620, 625 and 628 MACHINES
Remove arm too cover by opening stitch chart, re¬
moving screw, and sliding top cover toward left and
off the machine.
Remove arm top cover by removing the two screws
and lifting cover from machine.
Lay machine on back, loosen screws from the four
corners of the machine-bed cover, and remove cover
from underside of machine.
Wipe out any oil or grease accumulated inside
arm-toD and bed covers.
Oil machine as indicated below, and on pages
3, 4 and 5 for specific class of machine.
Apply one drop of oil between the casting and
the bobbin push-button release lever.

CLASS 626 MACHINES: This class of machine, supplied
only for use with the standard cam stack, does not require
the access means provided by the hinged top cover. Ac¬
cordingly, the following instructions do not apply to Class
626 Machines.
Removal
Remove top cover from machine as'described on
page 3.
Remove the two self-tapping screws on underside of
cover holding bracket to cover.
Remove holding ring from top lid.
Remove stitch indicator chart from lid.
Remove self-tapping screws in lid, disengaging
hinge.
Replacement
Fasten new hinge in lid with self-tapping screws.
Replace stitch indicator in top lid and secure it with
the holding ring-
Replace self-tapping screws through bracket. Do
NOT tighten securely.
Loosen adjustment screws in bracket.
Adjust lid so that it is flush with top cover. (This
is done by raising and lowering the lid on the slots
provided in the bracket while the adjustment screws
are loose, and by adjusting it to the left or right
while the self-tapping screws are loose in the over-
sized holes.)
When lid is correctly fitted, tighten the self-tapoing
screws and the adjustment screws in the bracket.
Replace cover and secure it with two cover screws.

THE ROTATING HOOK
VERTICAL GEAR
Removal
CAUTION: Hook-shaft gears and hand-wheel gea»
may be removed to facilitate adjustments. DO NOT
DISTURB THE MESH OF ANY OTHER GEAR IN
THIS MACHINE. All other gears are mated and cor¬
rectly timed. Replacements should be made only at
the factory.
Remove needle, presser foot, throat plate, bed
slide, bobbin case, feed dog, cushion-spring bracket,
and position finger.
Remove bed cover.
Remove feed-1 iftinq rock-shaft and feed rock-
shaft with pull-off finger as instructed on page 25,
Service Manual for Classes 600 and 603 Machines.
Remove actuating lever and bobbin driver as in¬
structed on page 9.
With chalk or crayon, mark the two bevel gears
as illustrated. (Mark one tooth of one gear, and the
corresponding space for that tooth in the other gear.)
This assures proper mesh when replacing.
Loosen set screw in vertical bevel gear, and re¬
move gear from hook shaft.
Lift rotating hook assembly from machine.
Replacement
InstalI rotating-hook assembly into machine. Using
the guide marks previous ly made, mesh vertical bevel
gear with horizontal bevel gear. Turn vertical hook-
shaft until flat side of shaft is under set screw in
bevel gear, and tighten set screw securelv.
Replace bobbin driver and actuating lever, as
instructed on page 9.
Insert pull-off finger into machine and reoiace
feed rock-shaft and feed-lifting rock-shatt as in¬
structed on page 25, Service Manual for v-lasses 600
and 603 Machines
Check and adjust hook as instructed on pages
7 and 3.
Replace all other parts previously instructed for
removal, except in reverse order.
6

To Time the Hook
Sot noodle bar at correct height, and time the
needle-bar vibrating mechanism as instructed on
pages 7 and 8, Service Manual for Classes 600 and
603 Machines.
Insert a Size 18 needle up into the needle clamp.
Remove throat plate, bed slide, bobbin case, and
bottom cover. It is not necessary to remove the feed
dog to time the hook.
Adjust machine for straight stitching in center
needle position.
Turn hand wheel over toward operator until lower
timing mark is aligned with lower edge of needle-
bar bushing on UPWARD STROKE of needle bar. At
this position, point of hook should be at center of
needle as illustrated.
To adjust, loosen the two set screws in horizontal
bevel gear. While maintaining position of needle bar,
turn vertical bevel gear at hook-end of shaft until
point of hook is in correct position. Then tighten
the two bevel-gear set screws securely, making cer¬
tain that gears are correctly meshed without binding.
CAUTION: Hub of horizontal bevel gear should
not contact face of bushing.
Replace throat plate, slide plate, bobbin case,
and bottom cover.
VERTICAL BEVEL SETSCREWS HCRIZONTAL 3 EV EL
\ SEAR
GEAR HUB SHOULD
HOT CONTACT FACE
OF BUSHING
7

To Position Hook to or from Needle
Set needle bar at correct height, and time the
hook as previously instructed.
Turn hand wheel until point of hook is directly
behind needle. When correctly set, the distance be¬
tween the needle and hook-point should be approx¬
imately 0.004 inch, as illustrated.
HOOK
POINT
SETTING: With bobbin push-button in winding
position, remove locator nut by turning in a CLOCK¬
WISE direction. Remove bobbin push-button assembly
(see instructions on poge 9), and remove locator.
Careful ly mark the two bevel gears, as illustrated,
to assure proper meshing of gears when replacing.
Then loosen set screw in vertical hook-shaft bevel-
gear and remove gear from shaft.
Loosen set screw holding the eccentric bushing.
Turn the eccentric bushing while maintaining posi¬
tion of hook, until correct distance between needle
and point of hook is attained.
Replace bevel-gear using the previously-made
guide marks to assure correct meshing of gears.
Replace all other parts in reverseorder instructed
for removal. Set winding mechanism as instructed
on page 9.
CAUTION: Check for binding or end play in hook
dri ving-s haft. F or adjustment and removal, see page
24 of Service Manual for 600 and 603 Machines, and
page 6 of this supplement for removal of hook.
s

WINDING MECHANISM
Bobbin Push-Button Assembly
Removal and Replacement
Open slide plate. Place push-button irr winding
position. Lay machine on back and remove bed cover
from machine. Remove locator nut from bobbin driver
by turning in a CLOCKWISE direction. Then remove
the two screws fastening the push-button assembly
to the underside of the bed. Slide assembly out as
a complete unit, being careful not to bend the push¬
button release lever.
To replace, follow the same directions as for
removal, except in reverse order.
Bobbin Driver
Removal and Replacement
Teen slide aiaTe. Remove ‘hroat plate, bobbin
cose, one ;ea cover. Per stitch enern seiecrcr ct p
•r.'cnes oer nen, one -pm non a -vneei jnri: eec
cog. is m its extreme 'ear oosinon. Remove iocaror
nut, pusn-button assembly, and locator. Then slide
bobbin driver up, rotate until apron is opposite feed
dog, and lift out of machine.
To replace, install bobbin driver in machine, ro¬
tating it until it seats firmly into place. Then replace
locator, push-button assembly, locator nut, throat
piate, and bobbin case.
Adjustment
To adjust the height of the bobbin driver, place
push-button in winding position and loosen adjustable
extension screw at end of lifting bracket. Press up¬
ward on bracket until bobbin rises slightly above top
of bobbin case. Then release upward pressure slight¬
ly, allowing bobbin to seat correctly into bobbin
case. Without disturbing this setting, tighten ex¬
tension screw securely
9

NEEDLE-THREAD TENSION ASSEMBLY
STUD CHECK SPRING
RELEASING PIN
SET SCREW
THREAD GUARD
Removal and Disassembly
Open face plate, loosen stud set-screw and re¬
move entire tension assembly, as illustrated. Loosen
set screw in dial and remove dial. Turn adaptor to
left until it is free from the stud. Remove indicator
stop, spring, cup, and tension releasing-pin. The
check spring, tension discs, and thread guard should
be removea from ‘he stud as a unit.
Reassemoiv and Rsoiacement
Replace releasing-pm in stud. Place tension
discs on the thread guard, align coil of check spring
with holes in tension discs and thread guard, and
place assembly on stud with tail of check spring
entering top groove of sprocket on stud. Replace cup,
spring, indicator stop (with tab at bottom position),
and adaptor. Replace dial, making certain that stop
on inside of dial is in contact with left side of in¬
dicator-stop tab when dial is set at zero (0) tension.
Tiahten set screw and place entire assembly onto
machine, with check spring resting on the top sur¬
face of the check-spring stop.
Adjustments
For adjustments of the needle-thread tension,
check-spring stroke, check-spring tension, and bob-
bin-case latch tension, refer to pages 21 and 22 in
the Service Manual for C!asses600 and 603 Machines.
10

THROAT-PLATE POSITION BRACKET
y
Removal and Replacement
Remove throat plate, and set throat-plate posi¬
tion lever in REGULAR position. Press left end of
position bracket toward underside of machine bed
as far as possible, and remove adjusting screw.
Swing left end of bracket away from machine bed
and remove the two throat-plate clamps with brackets,
pins, and springs. Set position lever in DARN posi¬
tion and remove screws from indicator plate. Lift
indicator plate, stop plate, and stpp-plate spring
from machine bed, and remove position bracket from
underside of machine.
Replace throat plate position bracket in reverse
order of its removal, but observe the following:
Stop plate spring should be replaced with the
curved portions of spring under cross-piece
of lever. Remainder of spring should extend
toward left.
Position bracket must be inserted in grooves
under machine bed.
Adjusting screw should be turned in flush
with bottom of casting while pressing left
end of bracket toward underside of bed.

RemovaI
Remove top cover.
Remove tension stud.
Remove two screws holding front stop, and selec¬
tor mechanism assembly.
Remove the front stop.
Disengage tension-arm spring from selector mech¬
anism.
Remove selector mechanism assembly.
Replacement
Replace selector mechanism assembly in the
machine, fastening it in place with the left screw.
Place the front stop on top of the mounting brack¬
et, and fasten it with the right screw.
Place tension arm over stud hole, being sure that
the arm is behind the arm plate.
In sert tens ion stud.
Loosen the left and right screws (which were
tightened previously on selector assembly and front
stop), and set the bracket parallel with the cross
shaft until the right edge of the bracket is approxi¬
mately L 16” to 3/32” from the cast boss for the
cross-shaft bearing.
Then re-tignten screws.
Engage driving spring, being sure that tail of
spring is up when put into place on release lever.
Again, loosen right screw of mounting bracket and
set stop to limit travel of selector arm (This is done
to prevent disengagement of the selector arm and the
follower, and yet give free movement to the selector
arm when selecting patterns.)
Replace top cover.
12

THE RELEASE MECHANISM (Cont'd)
Adjustments
Setting the Release Mechanism
Remove arm top cover.
Be sure stitch pattern selectors are properly en¬
gaged. Otherwise, machine will not engage when in
operation. If machine does not engage after selectors
are engaged, the releasing mechanism requires ad¬
justment as follows:
Loosen bracket screw in adjustable bracket and
engage release mechanism by swinging the bracket
to the right by hand until it engages. Tighten screw.
Front Stop and Selector Mechanism Assembly
REAR RETURN SPRING FRONT RETURN SPRING
E3 jmm
rear stop
BUSHING (SPLIT)
M3
FRONT RETURN SPRING
CAM SELECTOR ARM SHAFT FOR 626 MACHINE
Loosen screw on adjustable lever ana move the
lever until it mcKes contact with the plastic sieeves.
— .rn -ana .vheei to ns are enaacsment or •eieasmc
ever. Rs- r : a n t sn screw sec’jrsiv.
Setting the Loading Cam
The Loading Cam should be pre-set to within
1/32 to 1/16 inch from cross-shaft boss, as shown.
13

CAM STACK
SPRING
SCREW
STUD
CAM STACK
CLASS 626 MACHIN ES: This class of machine is designed
for use only with the factory-installed standard cam stack,
and is provided only with a Front Cam Selector Arm. Ac¬
cordingly, removal and replacement of cams in this ma¬
chine should be performed only by authorized servicemen
during regular maintenance periods, and those instructions
referring to Rear Com Selector Arm do not apply to Class
626 Machines.
CLASS 628 MACHINES: This class of machine is designed
for use only with one replaceable Fashion Disc stitch-
pattern cam during any one sewing operation, and is pro¬
vided only with a Front Cam Follower. Accordingly, those
instructions referring to Cam Stack Removal and Replace¬
ment, Adjustments, and Stops do not apply to Class 628
Mach ines.
Removal and Replacement
Set stitch pattern selector at “A — K”.
Remove arm top cover and removable Fashion
Disc fstitch-oattern cam).
Remove large screw-stud with its spring.
Remove cam stack.
Replace cam stack, meshing worm wheel of cam
stack with worm of arm shaft.
Reolace screw-stua with its SDring.
Replace Fashion Disc ana arm rop cover.
Aai u srmenrs
i iming the Cam Stack
Remove arm top cover and Fashion Disc, and
large screw-stud with its spring.
Using stitch-pattern selector, bring rear follower
in contact with edge of top cam of cam stack.
Turn hand wheel over toward operator until timing
mark is at point of contact with rear follower, as
shown.
At this setting, the needle bar should be at its
lowest position.
Loosen each of the three clamping screws on top
of cam stack.
While holding needle bar at its lowest position,,
manually rotate entire cam stack clockwise until
timing mark reaches point of contact with rear follow¬
er, as shown.
Tighten the three clamping screws.
Replace stud with its spring. Tighten stud.
Replace Fashion Disc and arm top cover.
14

THE CAM STACK (Cont’d)
Removal and Replacement
Remove arm top cover and control panel.
Remove cam stack as previously instructed on
page 14.
Loosen the clamping screw in lower selector arm
by inserting screwdriver through hole in upper arm.
Remove locating screw from plastic cam.
Remove the screw in rear follower arm.
Loosen the rear-stop-bushing set-screw.
Withdraw selector-arm shaft from rear of machine
arm, releasing front selector-arm and return-spring,
plastic cam, spring, rear selector-arm, and rear se¬
lector-arm return-spring.
Remove selector arms from machine.
Remove two followers from index pins.
Replace two followers, and replace selector arms
with cam and return-springs in position, making cer¬
tain that hinged brackets fit into slots in followers.
Replace selector-arm shaft through follower arms.
Replace rear follower-arm screw making certain
that it clamps down on flat part of shaft.
Tighten rear-stop-bushing set-screw securely.
Tighten the damning screw in lower selector-arm.
Rsdiccs ram stack.
Cneck one aajust the release mechcmsm as ; n -
Aa i u stmen r s
Setting the Index Pins
Set stitch selectors at “J” and "R”.
Remove arm top cover and control panel.
At this setting, top surface of two arm followers
should be approximately 1/64 inch below top surface
of c am stack.
NOTE: Position of two arm followers is determined
by height or index pins.
Loosen rear index-pin set-screw.
Raise or lower rear index-pin as required, to bring
top surface of rear follower 1/64 inch below top sur¬
face of cam stack, then tighten set screw securely.
Loosen front index-pin set-screw at front of ma¬
chine arm.
Raise or lower front index-pin as required, then
tighten set screw securely.
15

CAM STACK (Cont’d.)
Setting Cam-Selector-Arm Stops
Remove arm top cover.
Check adjustment of worm wheel shaft (see in¬
struction on page 17).
Set selector at “D" and “L 1 * .
Turn hand wheel over toward operator until arm-
bracket followers rest upon high points of bottom
(zigzag) cam of cam stack.
At this setting, when stitch pattern selectors are
depressed as far as possible, clearance between
both followers and high point of bottom cam should
be 0.010 and 0.012 inch.
Front Selector-Arm Stop
Disengage release mechanism by pushing in on
upper selector button.
Loosen screw in front selector-arm stop and de¬
press top selector button until there is approximately
0.010 inch clearance between front follower and cam.
Maintain this clearance while moving stop toward
front of machine until it makes contact with front
selector-arm. Then tighten screw securely.
Rear Selector Arm Stop
Loosen stop-bushing set-screw at rear of cam-
selector arm-shaft. ?-ess lower selector button until
there is ccDroximateiv 0.010 inch clearance between
■ e ar ' 0 ! lower one ram.
rlcintcin this set- ng vn: !e moving stoo ousning
•award '"rant at macrvne _nr; t maxes contact witn
rear - o l .ewer-arm, men rignten set screw securely.
Aligning Indicator with Selector Letters
Indicators “A” to “J”
Loosen set screw through hole in upper selector
arm.
Align indicator mark with “A” position on front
panel, making sure that rear follower is in contact
with aluminum bight-control ring (lowest ring with
largest diameter under the cam stack). Tighten set
screw securely.
Indicator “K” to “Special”
Loosen hex head screw in front follower arm.
Align indicator mark with ”K” position on front
panel, making sure that front follower is in contact
with aluminum bight-control ring (third ring from bot¬
tom under the cam stack). Then tighten hex head
screw

CAM STACK (Cont’d.)
Cam-Selector-Arm Shaft Return-Spring
Removal and Replacement
CLASS 620, 625 and 628 MACHINES:
To remove front selector-arm return-spring, follow
procedure described above for removal of cam-selec¬
tor-arm shaft down to withdrawal of shaft from rear
of machine.
As shaft is withdrawn, the tension-type return¬
spring can be lifted from between front and rear disc-
selector-arm brackets.
To replace, insert new return-spring between front
and rear disc-selector-arm brackets, slide shaft for¬
ward to engage spring, and reassemble cam-selector-
arm shaft and follower as described.
To remove rear selector-arm return-spring, follow
procedure described above for removal of cam-seiee-
tor-arm shaft down to removal of selector arms from
machine. This procedure releases coil-type rear re¬
turn-spring.
To replace, fit new return-spring on shaft and
reassemble cam-selector-arm shaft and followers as
described above.
Check ana adiust *he -eiecse mechanism as de¬
ar cec on cage '4.
CLASS 626 MACHINES
To remove selector-arm return-spring, follow pro¬
cedure described above for removal of cam-selector-
arm shaft down to withdrawal of shaft from rear of
machine,
As shaft is withdrawn, the tension-type return
soring can be lifted from the shaft between the legs
of the selector-arm bracket.
To replace, fit new return-spring on shaft and
reassemble cam-selector-arm shaft and follower as
described above,
Check and adjust the release mechanism as in¬
structed on page 14.
PRONT RETURN SPRING
620, 625 :na 623 Mac nines
REAR STOP BUSHING (SPLIT)
626 Machines
17

NOTE: The following instructions apply goneraily'to Class
620, 625, 626 and 628 Machines. As indicated on page 13,
however. Class 628 Machines must use the Sight-Amplitude
Selector in lieu of a Release Mechanism in order to neu¬
tralize the particular zig-zag stitch pattern provided by
the replaceable Fashion Disc utilized. Accordingly, the
section on page 20 dealing with Bight-Amplitude Adjust¬
ments will be particularly applicable to users of Class
628 Machines.
Removal and Replacement
Remove arm top cover, face plate, and control
panel.
Set stitch-pattern selectors at “A” — “K”.
Remove driving-arm spring.
Remove bight-lever screw from bracket, and re¬
move bight lever.
Loosen bight-amplitude set-screw and remove
entire cam stack assembly.
Remove bight-amplitude and pattern selector.
Replace pattern selector in the reverse order of
its removal.
Observe the following:
Assemble cam stack as a complete unit. Upper
eccentric half of worm wheel shaft should be turned
toward hand-wheel-end of machine, as shown.
Make certain that driving-arm ball-pivot is en¬
gaged with pattern selector.
Set mesh between worm of arm shaft and worm
wheel of pattern-selector by turning bight-amplitude
shaft clockwise so that there is no binding and a
minimum amount of backlash.
Tighten bight-amplitude set screw.
Replace driving-arm spring
Replace bight lever and fasten with set screw.
Adjust machine as instructed below and on fol¬
lowing page.
18