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CKU Single Disc Friction Clutch

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Bliss Press Parts

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The Bliss “CKU” clutch is a combination pneumatic friction clutch and spring-loaded disc brake. Compressed air is used to engage the clutch. When the air pressure is released, the springs set the brake.


The unit consists of two friction discs, one for the clutch (K-24), and one for the brake (K-17), Figures l and 2. Brake and clutch linings (K-5) and (K-7), respectively, are fastened on each side of these discs. (K-5) and (K-7) are furnished as assemblies. Other major parts consist of one driving disc (K-38), eight driving pins (K-45), two clutch friction disc pins (K-30), two brake friction disc pins (K-11), eight clutch springs (K-8), piston (K-9) with one packing (K-3), clutch body (K-1), air cylinder (K-46), clutch cylinder head (K-25), and the brake bracket (165A and 165B).

The clutch friction disc revolves with the flywheel while the brake friction disc is stationary. The clutch friction disc is held to the flywheel by clutch friction disc pins (K-30). The broke friction disc is held to the brake brackets by the broke friction disc pins (K-11). Both clutch and broke friction discs float on their respective pins. The clutch friction disc is guided on the pins by disc bushings (K-23}, and the brake friction disc by disc bushings (K-16).

The clutch and brake friction discs are separated by the driving disc (K-38) which rotates with the crankshaft, the clutch body (K-1), and the air cylinder (K-46). The driving disc is moved by air pressure to engage the clutch, and by spring pressure to set the brake.


To engage the clutch, compressed air enters the air cylinder (K-46) through the swivel shaft (AS- 1). As pressure moves piston (K-9), it compresses springs (K-8), moving the clutch driving disc (K-38) away from the broke disc (K-17) toward the clutch disc (K-24). This action forces the rotating clutch friction disc (K-24) between the driving disc (K-38) and the clutch body (K-l). As a result, the crankshaft star is rotating and transfers flywheel energy to the crankshaft. Air pressure must then be maintained to the air cylinder (K-46) during the operation of the press.

When air pressure is released, the brake springs move the driving disc away from the clutch disc and toward the brake disc. This grips the motionless brake disc, disengaging the clutch and creating the friction necessary to stop the crankshaft.

An air pressure faiIure wiII disengage the clutch and automatically set the brake.
NOTE: See figure 4 for clutch lining replacement.

CKU Single Disc Friction Clutch

76FlywheelK-29ARetainer screws
K-1Clutch bodyK-29BRetainer wire
K-3Piston packing, largeK-30Clutch frictin disc
K-5Brake lining-, 1 inner, 1 outerK-30A Clutch friction disc pin with flats
K-5ABrake lining, bolt & locknutK-38Driving disc
K-7Clutch lining, 1 inner, 1 outerK-45Driving pin-plain
K-9Brake springK-45ADriving pin w/lug
K-9PistonK-46Air Cylinder
K-11Brake friction disc pinK-48Clutch body screws
K-13Clutch and shaft keyK-48ALocking wire
K-16Brake friction disc bushingK-55Outer retaining ring (snap ring)
K-17Brake friction discK-61Clutch cylinder cover screws
K-18Snap ring disc pin retainer screw31-FWFlywheel bearing retainer screw
K-19Brake friction disc retainer screw33-FWFlywheel bearing
K-23Clutch friction disc bushing34-FWFlywheel bearing retainer
K-23AClutch friction disc bushing with flats42-FWFlywheel bearing adjusting shims
K-24Clutch friction discAS-1Air swivel assembly
K-25Clutch cylinder head165-ABrake bracket (lower)
K-26Clutch cylinder head gasket165-BBrake bracket (upper)
K-29Locking plate - (half circle)71End Plate
K-26CLocking plate - (rect angular)72Cap Screw
K-30BSnap ring72ALocking Wire

When ordering spare parts or replacement, give the PRESS NUMBER, the SERIAL NUMBER and NAME of the part wanted, and the PAGE NUMBER of the service manual.

On clutch sizes #12, #32 and #62 ball bearings are used. On clutch sizes #122 and #252 and up roller bearings are used.

WARNING: If it is necessary to disassemble clutch, remove two (K-48) clutch body screws and add two longer screws or studs. This is to prevent cylinder (K-46) from coming off shaft as spring (K-8) has tendency to separate cylinder and clutch body.

Parts List


1. Disconnect hose from AS-1 swivel.
2. Remove K-61 cap screws which will allow K-25 cylinder head to be removed. Be careful not to destroy K-26 gasket.
3. Remove K-9 piston.
4. Remove 72A and 72 cap screws and wire.
5. Remove 71 end plate.
6. Remove K-13 tapered key by use of jack sc rew and pry bar. Bottom jack screw before using pry bar.

When ordering spare parts or replacements, give the PRESS NUMBER, the SERIAL NUMBER, the NUMBER and NAME of the part wanted, and the PAGE NUMBER of this service manual. On clutch sizes #12, #32 and #62 ball bearings are used.

On clutch sizes #12, #32 and #62 ball bearings are used. On clutch sizes #122 and #252 and up roller bearings are used.

WARNING: If it is necessary to disassemble clutch, remove two (K-48) clutch body screws and add two longer screws or studs. This is to prevent cylinder (K-46) from coming off shaft as spring (K-8) has tendency to separate cylinder and clutch body.

Air service must be provided to operate the clutch. A single air line inlet is usually provided on the press, to which the shop air line must be connected. Piping is arranged so that all compressed air passes through a common filter or separator. Branch Iines leave the outlet side of the filter to the clutch and other air devices, when furnished. An air pressure regulator in each branch line maintains proper operating pressure for these devices. See Figure 3.

Recommended maximum operating air pressure is 70 P.S.I.

Actual requirement for each press is shown on an instruction plate attached to press frame, Figure A.

An airline lubricator is provided in the branch line to the clutch, and is installed between the clutch pressure regulator and clutch operating valve. The lubricator should be adjusted to a fine mist on every clutch engagement. Use a high grade straight mineral lubricating oil with a viscosity of 145-165 SSU & 100° F. SAE No. 10.

An air tank is required in the clutch line to reduce the pressure drop at each clutch engagement.

The airline filter bowl must be drained regularly for effective performance. There is a “drain cock” at lower end of bowl for this purpose. Never permit moisture to fill bowl above baffle or up to filter element, otherwise, collected moisture and emulsion may be carried into the airline.

Note that the air tank is also provided with drain cock to remove accumulated moisture.


Moisture in the air carried to the clutch will create rust and stickiness of the piston in the cylinder that can result in a dangerous condition in the clutch and valve. Moisture must be kept out of the air lines.

An air swivel and hose provide a flexible connection between the clutch operating valve and the crank shaft.

Figure 4 .
Furnished in one unit friction block & plate assembly.

K-SABroke lining plate bolt and nut
K-7AClutch lining plate nut and bolt
K-5Broke lining- l inner, l outer
K-7Clutch lining- l inner, l outer
K-23Clutch frict ion disc bushing
K-16Brake friction disc bushing
K-11Brake friction disc pin
K-30Clutch friction disc pin
K-24Clutch friction disc
K-17Broke friction disc

Clutch and Brake Lining Replacement

Figure 5 – This illustration indicates the ease with which the clutch friction plates can be replaced. This is accomplished without disassembling the clutch and with a minimum of down time.

The clutch and brake require no adjust ment during the Iife of the friction blocks, except as noted below, as the movement of the air piston increases to compensate for the wear. The replacement of the clutch and broke linings can be made without dismant ling the clutch. The clutch friction block assemblies are made in quadrants requiring four per friction face or or eight for each friction disc.

The lining assemblies can be removed by, first, removing the bolts and nuts (K-7 A} and then withdrawing the friction lining assemblies. New lining assemblies con be installed by reversing this procedure.


This is the same as mentioned above for the clutch except that air pressure must first be applied to release the brake disc. Be sure stroke is down when changing linings .

NOTE: When Brake lining and its bocking plate measure approximately 330”, replace it with new linings and backing plate. On the clutch lining, the above procedure con be used when the lining and its
backing plate wear 1 / 32”.

Bliss Clutch with Unsticker

This size model clutch....Generally fits on this model Bliss press...And generally this type of press uses flywheel type or single gear type.
12-CK UC - 22 , 19-1/2 - BFl ywhee l Type
32-CKUC-35 , 20- B , 21F l ywheel T ype
C - 35, 20 - B , 21Sing l e Gear T ype
C - 45, C-60 , 21-S, 21 8, 2 1- 112 , 2 1-1 /2-BFlywhee l T ype
122-CKUC - 45 , C-60 , 21 - S, 21 · 8, 2 1 -1/2, 21-1/2 - BSing l e Gear T ype
C - 75 , 23F lyw heel T ype
222-CKUC-75, 23S i ngle Gear Type
28, 28 - 1 / 2Flywhee l T ype
252-CKUC - 75 , 23Single Gear Type
C - 110 , 28, 28-1/2 , C-150Flywhee l Type
372-CKUC- 1 10 , 28 , 28 - 1/2S l ng l e Gear T ype
422-CK UC- 11 0 , 28, 28-1/2S i ngle Ge ar Type
442 - CKU28 - 1/2S i ng l e Gear Type
552-CKUC -1 50 , C - 200 (1hru 6 " stroke)Sing l e Gea r Type
922-CKUC - 200 , (8" stroke) C-250-(8" thru 12" stroke)S i ng l e Gea r Type

Procedure for using the “Bumper” on the Clutch

The Bliss unsticker is an impact device using a special bumper pin locked in the flywheel or gear as an interference between the clutch body and the flywheel or gear. When not in use the bumper pin is stored in a receptacle on the electric control enclosure.

To insure maximum safety and efficiency when unsticking a press, follow the procedure exactly as outlined below.

1. Stop Motor – Depress motor stop button, dropping out motor starter thereby signalling the motor and flywheel to stop. WARNING: Be sure both mot.or and flywheel have come to a complete stop before proceeding further.

2. Turn Bumper Selector Switch To “Bumper On” –  Do not remove bumper pin from control panel at this time.

3. Remove Cover Over Clutch Guard utility Opening – (For Figure 2 only.)  Remove Front Cover of “C” Press. (For Figure 1 only.)

4. Rotate The Flywheel – Using a spring-loaded bar in the holes in the rim of the flywheel, rotate the flywheel so that the bumper pin space or hole in the flywheel or gear can be seen and/or reached.


5. Remove Bumper Pin –  Remove bumper pin from receptacle on control enclosure and insert it into the bumper pin space or hole in the flywheel or gear mounted on the crankshaft and secure it . A thumb screw is provided for this purpose on the round pin, while the rectangular pin has a key lock.

CAUTION – The special bumper pin is designed for unsticking. Do not use any other material or device in lieu of the special bumper pin supplied with your press.

6. Determine Desired Rotation – If the slide is stuck before bottom dead center (BDC), arrange to rotate the crankshaft in a direction opposite to the normal shaft rotation.The bumping action will then cause the slide to move up and away from the die rather than down and into it. If the slide is stuck at or a little after BDC, the crankshaft can be bumped to rotate in its normal direction.

7. Select Proper Rotation – If the press is arranged with a reversing starter, set the selector switch to “forward” or “reverse” as required.

If the press is arranged with a non-reversing starter and a reverse direction is desired to unstick the press, it will be necessary to interchange any two of the three motor leads so that the motor rotation will be reversed.

8. Back Up Bumper Pin –  Manually rotate the flywheel in the direction opposite to the direction required to unstick the press until the bumper pin is in contact with the lug on the clutch hub that is opposite to the one that is to be bumped. There are two lugs on the clutch body so that only 180 degrees rotation of the flywheel or gear can be made to unstick the press.

9. Start Motor – Depress motor “start” & button momentarily. This action will cause the motor and flywheel to rotate and they will rotate only as long as the “Start” button is held depressed. Releasing the “Start” button will drop out the motor starter. It is not necessary to depress the motor “Stop” button. Hold the “Start” button depressed only long enough to have the pin bump the clutch lug.

If the slide does not come uns tuck after one blow. it may be necessary to repeat this action . Back up the rotating member until the bumper pin is in contact with one of the lugs and then depress motor start button again.

CAUTION- Immediately after bumping occurs, be sure to release the motor start button.

10. Turn Selector Switch to “Bumper Off” – After the slide is unstuck turn the “bumper off-on” selector switch to the “off” position.

11. Remove Bumper Pin – Rotate the flywheel with a bar until the bumper pin can be reached. Remove the bumper pin from the rotating element of the press. Do not replace Bumper Pin in the receptacle until motor starter has been checked out. Be sure to replace cover on press or on guard.

12. Check Motor Starter – If press is arranged with a reversing starter, check to see that the selector switch has been set to “forward.”

If a non-reversing starter was in use and the rotation had been reversed for the unsticking operation by changing motorleads, make sure that the leads are returned to their original positions.

13. Restore Bumper Pin – Replace bumper pin in the receptacle on the press control panel.

With the pin back in the receptacle, the motor starter can now be actuated to put the press back into operation.

Why use genuine Bliss parts?

① Good and Services Warranty

Purchase press parts with confidence from BCN Technical Services. We guarantee at the time of delivery, the goods will be free from defects in materials and workmanship. We will perform services in a prompt, professional and workmanlike manner. View our Goods and Services Warranty for details.

② Original OEM Specifications

Replacement parts are manufactured to original OEM specifications from record sets maintained by serial number, so there’s no guessing or wondering if a part will fit. We have original drawings, manufacturing expertise, and the experience of a team of engineers who know your press inside and out.

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BCN Technical Services has an extensive inventory of the most requested OEM replacement parts in stock at our facility in Hastings, MI. Over 14,000 unique spare parts for presses are kept on hand. Our experienced staff is dedicated to quickly providing that critical part, which allows you to avoid delayed repairs, lost productivity and lost revenue.

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