Model 797/797A/797B

Tune-Up Kit
Jacobs P/N 032146

This Tune-Up Kit requires Master Piston Assembly Tool, P/N J-45976. The tool is available through Kent-Moore.

Information in this manual was current at the time of printing and is subject to change without notice or liability.

Refer to the Application Guide, P/N 24770 for specific application information. Also refer to the Installation
Manual, P/N 29901 and the engine manual for specific installation instructions.

TUNE-UP KIT INSTRUCTIONS

 Tune-up Kit Contents
Qty. Qty.
Ill. Jacobs Ill. Jacobs
Part Name Per Part Name Per
No. P/N No. P/N
Kit Kit
1 1024612 Solenoid, 12VDC S/L 0 14 031854 Spring, Inner Slave Piston 6
1 1024619 Solenoid, 24 VDC S/L 0 15 031857 Spring, Outer Slave Piston 6
1 1034737 Solenoid, 12VDC D/L (797B Only) 0 16 031639 Bolt, Shoulder-Slave Piston 6
2 020229 Seal, Solenoid Upper 2/3* 17 012991 Ring, Retainer 6
3 001082 Seal, Solenoid Center 2/3* 18 016505 Washer 6
5 031282 Master Piston 0 19 018179 Spring, Inner Control Valve 6
6 028791 Push Rod, Master Piston 0 20 010843 Spring, Outer Control Valve 6
7 028768 Spring, Master Piston 6 21 011930 Control Valve 6
8 031854 Retainer, Master Piston 6 22 028317 Pipe Plug 0
9 031331 Ring, Retainer 6 23 017303 Drive Screw 0
11 031270 Solid Screw 3/8-24 (1” Long) 0 24 029127 Clip, Wire Harness 0
12 031324 Slave Piston 0 25 028346 Capscrew, M12X1.75X170 0
032127** Slave Piston Spring Group 26 029132 Capscrew, M12X1.75X140 0
13 031635 Bridge, Slave Piston 0 27 029118 Spacer Tube 0
*797A front housing has 2 solenoids and the rear housing has 1 solenoid.

14 13

15

16

**Slave Piston Spring Group

T U N E - U P K I T I N S T R U C T I O N S F O R 7 9 7 / 7 9 7 A / 7 9 7 B 2
 General Information Instructions
These instructions describe how to properly remove, clean N EVER REMOVE OR ADJUST ANY ENGINE
and reinstall Jacobs Vehicle Systems® components. For ad- BRAKE OR COMPONENT WITH THE
ditional information on the Model 797 engine brakes, refer to ENGINE RUNNING.
the Series 60 Engine Installation Manual, P/N 29901.
Access Engine Brake
For slave piston clearance refer to the Jacobs Application
Guide for Detroit Diesel Engines, P/N 24770. 1. Thoroughly clean engine.

2. Remove valve rocker cover and gasket.

Use OSHA-approved cleaning solvent for cleaning parts.
Original parts to be reused should be inspected for wear and IF THE ENGINE HAS A TWO-PIECE COVER,
replaced as required. Be sure to coat parts with clean engine THE LOWER VALVE COVER BASE DOES
NOT HAVE TO BE REMOVED TO GAIN AC-
oil when reinstalling them. CESS TO THE ENGINE BRAKE HOUSINGS.
3. Disconnect the lead wires from each of the solenoid
The standard Jacobs Vehicle Systems Service Parts Warranty valves (1) and detach them from the wire clips (24).
applies to the components of this Tune-up Kit. The warranty is
administered by Detroit Diesel Corporation. 4. Remove the six capscrews (25&26) and nut securing
each engine brake housing. Remove the housings.

5. Retain six spacer tubes (27).

Safety Precautions
The following symbols in this manual signal conditions Disassemble Housings
potentially dangerous to the mechanic or equipment. Read
this manual carefully. Know when these conditions can exist. 1. Remove the solenoid valves (1) and discard the seal
Then take necessary steps to protect personnel as well as rings (2,3).
equipment.
WEAR SAFETY GLASSES. REMOVE
THIS SYMBOL WARNS OF POSSIBLE CONTROL VALVE COVERS CAREFULLY
PERSONAL INJURY. TO AVOID PERSONAL INJURY. COVERS
ARE UNDER LOAD FROM CONTROL VALVE
THIS SYMBOL REFERS TO POSSIBLE SPRINGS (19,20).
! CAUTION
EQUIPMENT DAMAGE.
2. Hold down the control valve cover while removing the
INDICATES AN OPERATION, PROCEDURE retaining ring (17). Remove and discard all parts.
OR INSTRUCTION THAT IS IMPORTANT
FOR CORRECT SERVICE. 3. Loosen the locknuts (10) and remove the adjusting
screws (11) and locknuts. Retain the adjusting screws
Fuels, electrical equipment, exhaust gases and moving engine and locknuts.
parts present potential hazards that could result in personal
injury. Take care when installing equipment or parts. Always 4. Remove the shoulder bolt and springs (14,15) that retain
wear safety glasses. Always use correct tools and follow the slave pistons; discard springs and shoulder bolts.
proper procedures as outlined in this manual. Remove and save the bridge (13) and slave piston (12).

5. Remove master piston retaining ring (9), master

piston retaining washer (8), master piston spring (7),
master piston pushrod (6), and master piston (5). Use
caution while removing the master piston retaining ring.
Excessive prying against the master piston bore may
cause damage. Retain master piston and pushrod.
Discard all other components.

3
 WEAR SAFETY GLASSES WHILE
Assemble Housings BLOWING THE OIL FROM THE BOLT
HOLES.
1. Clean all parts in an approved cleaning solvent. Dry with
1. Set front and rear Jake Brake housings on rocker shafts
compressed air.
locating on retorqued studs. Ensure that master piston
pushrods will engage with pocket located on top of
2. Coat all parts to be installed into housings with clean
injector rocker arm.
lube oil.
2. Lubricate each hold-down capscrew with clean engine oil
3.  einstall all original slave pistons (12) and bridges (13),
R
prior to installation.
reversing the removal procedure.
3. Install three M12x170 capscrews (25) on solenoid side
4. Install the new shoulder bolts (16) and springs (14,15).
of brake. Install three M12x140 capscrews (26) on the
Tighten the bolts to 23 Nm (200 lb-in).
exhaust side of the engine.
5. Re-install original master pistons (5) and pushrods
INSTALLING 170 MM CAPSCREWS (25)
(6). Install new master piston springs (7). Use master
! CAUTION ON THE EXHAUST SIDE OF THE ENGINE
piston assembly tool (P/N J-45976 from Kent-Moore)
CAN RESULT IN SERIOUS ENGINE
to install master piston retainers (8) and retaining rings
DAMAGE.
(9). Visually inspect to ensure the retaining rings are fully
engaged.
4. Before tightening the capscrews, move the housing from
side to side. Position housing in the center of the range
6. Install the adjusting screws (11) and locknuts (10). Do
of motion.
not tighten the locknuts at this time.
5. Tighten the capscrews or nuts per sequence in figure
7. Install the new control valves (21), springs (19,20),
below at 80 lb-ft (180 Nm).
washers (18) and retaining rings (17). Rotate the
retaining ring 90° after installation to ensure that the ring
is seated in the groove.

8. Install the upper (2) and center (3) seal rings on the
solenoid valves. Coat the seals with engine oil prior to
assembly.

NEW UPPER SEAL RINGS CAN BE

IDENTIFIED BY A YELLOW STRIPE

9. Insert the solenoid valves and torque to 20 Nm (15 lb-ft). 6. Verify exhaust and intake valve lash is still within DDC
specifications for engine. If valve lash is out of tolerance,
INSTALL THE SOLENOID CAREFULLY refer to DDC manual for resetting procedure.
TO AVOID CUTTING OR TWISTING THE
SEAL RINGS. IMPROPER INSTALLATION 7. Connect the lead wires to the solenoid valves passing
COULD RESULT IN POOR ENGINE BRAKE the wires through the wire clips.
PERFORMANCE.
8. Torque solenoid screw to 1 Nm (9 lb in).

Install Engine Brake Housings 797B APPLICATIONS UTILIZE A DDC

WIRE HARNESS TRAY WHICH IS AT-
REMOVING THE OIL FROM THE BOLT TACHED ONTO THE REAR BRAKE HOUS-
HOLES PREVENTS THE CYLINDER ING - WIRE CLIPS DO NOT APPLY TO
HEAD FROM CRACKING WHEN BOLTS THIS MODEL.
ARE TIGHTENED. ATTACH A LENGTH
! CAUTION OF TUBING TO AN AIR GUN NOZZLE REFERENCE THE DDC SERIES 60 EN-
AND BLOW OUT THE OIL FROM THE GINE SERVICE MANUAL P/N 6SE483 FOR
HOUSING HOLD-DOWN BOLT HOLES. PROPER TRAY TORQUING PROCEDURE.
COVER THE HOLES WITH HAND TOWELS
TO MINIMIZE OIL SPRAY.

T U N E - U P K I T I N S T R U C T I O N S F O R 7 9 7 / 7 9 7 A / 7 9 7 B S E R I E S 4
 2. Watch the slave piston assembly. It should move
Adjust Slave Piston Clearance down to contact the exhaust valve rocker arm adjusting
screws.
FAILURE TO FOLLOW ADJUSTMENT
3. Check each housing to be sure it is functioning.
! CAUTION PROCEDURES CAN RESULT IN ENGINE
OR ENGINE BRAKE DAMAGE.
4. Shut down engine.
MAKE SLAVE PISTON ADJUSTMENT
WITH THE ENGINE STOPPED AND
COLD. ADJUST EACH CYLINDER WITH
THE EXHAUST VALVES IN THE CLOSED
POSITION.

1. Back out the adjusting screws on the slave pistons until

the slave piston does not touch the rocker arm.

2. Insert the proper feeler gage between the slave piston

and the exhaust rocker adjusting screw. Using a 3/16
inch hex wrench turn in the adjusting screw until the
slave piston contacts the exhaust rocker adjusting screw
through the feeler gage.

3. Hold the adjusting screw in place and torque the lock

nut to 38 Nm (336 lb-in). Recheck lash settings. If lash
setting is incorrect, repeat steps (1) through (3) above.

Engine Brake Operational Check

WEAR EYE PROTECTION AND DO NOT
EXPOSE YOUR FACE OVER THE ENGINE
AREA. TAKE PRECAUTIONS TO PREVENT
OIL LEAKAGE ONTO THE ENGINE.
COVER CONTROL VALVE AREAS
SUFFICIENTLY TO PREVENT OIL SPLASH.

Bleed the engine brake housings.

1. Be sure wires are away from moving parts.

2. Start the engine and allow to run for a few minutes

3.  anually activate the solenoid valve several times to

M
allow the housing to be filled with oil.

THE SOLENOID VALVE IS MANUALLY

ACTIVATED BY DEPRESSING THE
ARMATURE. THE ARMATURE IS LOCATED
IN THE CENTER OF THE TOP OF THE
SOLENOID.

Check for proper operation.

1. Manually activate the solenoid valve and watch that the

master piston pushrod is moving down into the injector
rocker arm pocket.

5
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