Engine Brake, Fault Tracing

Service Bulletin Trucks

Volvo Trucks Trucks North America, America, Inc. Greensboro, NC USA

This Service Bulletin replaces SB 253–21, “Engine Brake, Fault Tracing, Checklist O, D12D” (11.02), publication no. PV776–TSP170589.

Date

Group

No.

3.2003

253 21

Page

1(21)

Engine Brake Fault Tracing Checklist O D12D

Engine Brake, Fault Tracing Checklist O

T2019344

This information covers fault tracing the VEB (Volvo Engine Brake) for the Volvo D12D engine.

Contents Guide to Fault Tracing” page 2 • “General Guide • “System Overview” page 3 • “Checklist O, Engine Brake” page 10 Brake, Fault Fault Tracing” Tracing” page 12 • “Engine Brake, NOTE: Information NOTE: Information is subject to change without notice. Illustrations are used for reference only, and may differ slightly from the actual engine version. However, key components addressed in this information are represented as accurately as possible.

PV776-TSP187872

USA13254

Volvo Trucks Trucks North America, America, Inc. Service Bulletin

Date

3.2003

Group

25 2 53

No.

21

General Guide to Fault Tracing (See also “Engine Brake, Fault Tracing” page 1.)

You must read and understand the precautions and guidelines in Service Information, group 20, "General Safety Practices, Engine" before performing any procedure. If you are not properly trained and certified in a procedure, ask your supervisor for training before you perform it.

To use this checklist: 1

• • •

2

Use the recommendations recommendations in appropriate symptom symptom information, information, plus the inforinformation gathered above to provide a foundation for continued fault tracing using this checklist.

Complete basic data gathering gathering Read fault codes Check vehicle parameters

One fault often affects other systems. Therefore, it is important to confirm or eliminat eliminate e suspected suspected causes of faults faults at an early early stage, stage, using using tests tests in VCADS Pro.

Page

2(21)

Volvo Trucks North America, Inc. Service Bulletin

Date

3.2003

Group

253

No.

21

Page

System Overview

W2004194

When fault tracing, it is important to understand the function of the system and to follow the fault tracing sequence in the checklist to avoid replacing nondefective components.

3(21)


Date

3.2003

Group

253

No.

21

Component list Component Description A12

Control unit, ABS

A14

Control unit, EECU (engine electronic control unit)

A17

Control unit, VECU (vehicle electronic control unit)

A27

Control unit, LCM (external lighting)

B04

Sensor, engine speed, crankshaft

B13-18

Sensor, wheel speed

B25

Sensor, accelerator pedal

B37

Sensor, intake manifold pressure and temperature

B38

Sensor, oil pressure and oil temperature

B68

Sensor, road speed

F80

Fuse, engine solenoid valves, or fuel pump

S07

Switch, engine brake

S58

Position switch, clutch pedal, NC at rest

Y37

Air valve unit (AVU), engine brake/exhaust pressure governor (EPG)

Y39

Solenoid/control valve, VCB (Volvo Compression Brake)

Page

4(21)


Date

Engine Brake For additional information on the design and function of the Volvo Engine Brake, refer to Service Information, group 25.

3.2003

Group

253

No.

Page

21

5(21)

EPG Switch (S07)

There are two options for engine braking:

Exhaust brake, EPG The exhaust pressure governor (EPG) uses a shutter mounted in the exhaust outlet from the turbocharger. This shutter, connected to the EPG plunger, can restrict the exhaust gas flow. This creates a braking effect during the exhaust stroke when the exhaust gases cannot evacuate freely; they create an overpressure between the pistons and the shutter.

T0008637

Two positions.

For a more detailed description of the EPG function, see “Exhaust Pressure Governor (EPG)” page 7.

Engine brake, VEB The Volvo Engine Brake (VEB) consists of two systems: the exhaust brake (see “Exhaust brake, EPG” page 5) and the compression brake. The EPG creates an overpressure in the exhaust, making the compression brake more efficient. The VEB includes a special rocker arm for the exhaust valves, a special camshaft with extra cams and a solenoid valve for oil pressure in the rocker arm. For a more detailed technical description, see “Compression Brake” page 8.

The position of the switch

Engine brake

0 (switched off)

0%

1

100 %

Electrical control With the switch in position 1, the exhaust brake is activated when the accelerator (B25) is released.

The braking effect of the compression brake on the engine occurs when:

The information from the switch and the accelerator go via the vehicle control unit (A17) through the data links (J1939 and J1708/J1587) to the engine control unit (A14). The engine control unit then sends a PWM signal (Pulse Wide Modulated) to the AVU (Y37), which sends out full control pressure (7.5 bar/110 psi) to the EPG. The AVU is given voltage via fuse F80.

•

Requirements

•

The exhaust valve opens and allows air in during the intake stroke , which gives more air to compress during the compression stroke. The exhaust valve opens immediately before the turn of the compression stroke and ”punctures” the compression in order to reduce the effect with the working stroke.

Electrical control of engine brake The engine brake power is determined by the driver’s settings. The power varies for different combinations of engine brakes.

• • • •

Clutch pedal (S58) is NOT depressed. Engine speed exceeds 900 rpm; engine speed sensor, B04 (deactivates < 800 rpm). Speedometer (B68) indicates a speed greater than 5 km/h (3 mph). ABS wheel sensor (B13-18) indicates NO wheel lockup (ABS non-active).


VEB

Date

3.2003

Group

253

No.

21

Page

6(21)

Electrical control When the switch is in position 1 the exhaust brake is activated when the accelerator pedal (B25) is released. EPG is activated with full control pressure (7.5 bar/110 psi) from the air valve unit, or AVU, to attain 50% engine brake.

Switch (S07)

When the switch is in position 2 the VCB is activated, when the accelerator pedal (B25) is released. At the same time, the EPG is activated with full control pressure to attain 100% engine brake.

The position of the switch

Engine brake

0 (switched off)

0%

The information from the switch and the accelerator go via the vehicle control unit (A17) through the data links (J1939 and J1708/J1587) to the engine ECU (A14). The engine ECU then sends a signal (-) to the solenoid/control valve (Y39) for increased oil pressure in the rocker arm shaft and a PWM signal (Pulse Wide Modulated) to the AVU (Y37). Both the control valves are supplied voltage via fuse F80.

1

50 %

Requirements

2

100 %

T0008058

Three positions.

• • • • • • •

Clutch pedal (S58) is NOT depressed. Accelerator pedal (B25) released. Engine speed exceeds 1100 rpm*; engine speed sensor, B04 (deactivates < 1000 rpm). Speedometer (B68) indicates a speed greater than 5 km/h (3 mph). Oil temperature (B38) greater than 55 C (131 F). Intake manifold pressure (B37) less than 50 kPa (7.25 psi). ABS wheel sensor (B13-18) indicates NO wheel lockup (ABS non-active).

NOTE: *Activation rpm is raised by 300 to 1400 rpm when oil temperature is 55 – 82 C (131 – 180 F) or after the first 5 engine brake requests.


Date

3.2003

Group

253

No.

21

Page

7(21)

Exhaust Pressure Governor (EPG)

W2004195

The exhaust pressure governor has three functions:

Start and heat retention

•

To keep the engine warm when idling.

•

To function as exhaust brake on down gradients.

For functional description and fault tracing of the exhaust pressure governor during start and heat retention, refer to Service Information, group 25, “EPG, Fault Tracing, Checklist E.”

•

To apply exhaust back pressure during idle EGR function.

The exhaust pressure governor is situated in direct connection to the turbo’s turbine housing. The exhaust pressure governor consists of a shutter housing (1), a shutter (2) and a compressed air operated cylinder (3). The compressed air is supplied from the vehicle’s compressed air system and is regulated by the AVU, located on the intake side of the engine (4), and releases a reduced pressure to the exhaust pressure governor. The PWM-type valve controls the pressure steplessly within 0.5 – 7.5 bar (7 - 110 psi). Under normal driving conditions, the AVU (4) is closed. The shutter (2) is then completely open and the exhaust passes freely.

Exhaust brake The EPG is activated by control pressure of approximately 7.5 bar (110 psi). The shutter (2) is forced into the shutter housing (1) which restricts exhaust flow and causes back pressure in the exhaust. If the engine is equipped with VEB (Volvo Engine Brake), the compression brake and EPG are activated simultaneously to attain 100% engine brake (switch position 2).


Date

3.2003

Group

253

No.

21

Page

8(21)

Compression Brake Solenoid/Control Valve

T2019494

The solenoid/control valve has the task of regulating the oil pressure to the rocker arm mechanism. The inlet (1), which is connected to the lubricating oil passage in the cylinder block, always has system oil pressure. The outlet (5) is connected to the rocker arm shaft. The compression brake is activated by the solenoid valve (2), which is controlled from the EECU.

A: When the engine is running the piston (3) partly covers the outlet (5), which results in reduction of oil pressure to approximately 100 kPa (14.5 psi) after the solenoid valve. This oil pressure is sufficient for lubrication of the camshaft bearings and the rocker arm mechanism. B: With compression braking, voltage to the solenoid valve (2) opens a draining passage. The oil in the oil space (6) flows out through the draining passage, allowing the spring (4) to push the piston (3) to the side. This means the outlet (5) becomes free and the oil pressure from the gallery connection provides the rocker arm shaft with full oil pressure — more than 200 kPa (29 psi).


Date

3.2003

Group

253

No.

21

Page

9(21)

Camshaft and exhaust rocker arms

W2004196

The camshaft (1) on an engine with VCB has, in addition to the ordinary exhaust cam (2), a charge cam (3) and a decompression cam (4) on each exhaust cam lobe. Each rocker arm (5) includes a non-return valve (7) and a rocker arm piston (8). A spring tab (6) holds the rocker arm in its resting position against the valve bridge. The non-return valve clearance is adjusted with the help of shim (9) which is situated on the valve bridge. The non-return valve (7) consists of a piston (11) and spring (14), spring (12) and ball (13). A: Under normal engine operation, the solenoid/control valve reduces the oil pressure. At reduced oil pressure of 100 kPa (14.5 psi), the piston (11) will not move out of its rest position, because the oil pressure is not sufficient to overcome the spring force (14). The piston’s pin holds the ball (13) away from the seat, which allows the oil to flow in both directions through the non-return valve. This prevents excess oil pressure building up above the rocker arm piston (8). In this position the exhaust valves are not affected by the extra brake cams on the camshaft.

B: With compression braking, the solenoid/control valve increases the oil pressure to > 200 kPa (29 psi). At high pressure, the piston (11) overcomes the spring (14), which means that the spring (12) can push the ball (13) towards the seat. The oil, above the rocker arm piston (8), can no longer flow past the ball and therefore pushes on the rocker arm piston (8), so that the piston pushes down and eliminates the valve clearance. When the camshaft’s extra brake cams (3) and (4) further affect movement of the rocker arm, the exhaust valves are pushed down and compress (force more air into the cylinder with the help of the back pressure in the exhaust during the compression stroke) and decompression respectively (release compression during the power stroke). So that the pressure above the rocker arm piston does not push back into the rocker arm shaft when the valve opens, there is a pressure limiting valve (10).


Date

3.2003

Group

253

No.

Page

21

10(21)

Checklist O, Engine Brake See also:

• •

“General Guide to Fault Tracing” page 2 “Engine Brake, Fault Tracing” page 12 Vehicle

Chassis no.

Mileage

Customer Yes

1

“Fault Codes, Checking” page 12 Have the fault codes related to the engine brake been corrected? Action:

2

Engine Brake Checks (VCADS Pro: "Engine Brake Function, test") Does the displayed status conform to the actual position of the switch?: Switch Status Position 1 (EPG) Position 2 (EPG and VCB)

Does the switch receive voltage from the VECU? Do EPG and VCB solenoid valves function when activated by VCADS Pro? Does the EECU give signals to the AVU? Does accelerator pedal idling switch indicator light up when pedal is depressed ... and go off when pedal is released? Road test — Check the following requirements (for the engine brake to become active) during test driving:

Measured accelerator position

%

Is the accelerator position 0% (pedal released)? Does the displayed status conform to the position of the clutch pedal? Is the fuel volume 0 (no fuel injection)? Is vehicle speed above 0 km/h (0 mph)? Is the oil temperature above 55 C (131 F)? Is the charge pressure less than 50 kPa (7 psi)? Is engine speed above 900 rpm for EPG activation? Is engine speed above 1100 rpm for VEB activation? [Or 1400 rpm if oil temp is 55 - 80 C (131 - 180 F)] Is EPG solenoid valve indicator lit in switch position 1 when prerequisites are met? Are VEB and EPG solenoid valve indicators lit in switch position 2 when prerequisites are met? Action: 3

“Air Supply to EPG and AVU, Checking” page 12

AVU (air valve unit) Does the AVU receive correct air pressure (over 7.5 bar / 110 psi)? Are the air hoses correctly clamped and free from kinks or damage? Does the EPG receive correct air pressure at 100% activation (approx. 7.5 bar/110 psi)? Action:

bar (psi)

No

Volvo Trucks North America, Inc. Service Bulletin Vehicle

Chassis no.

Date

Mileage

3.2003

Group

253

No.

Page

21

Customer Yes

4

“Shutter Travel, EPG, Checking” page 13 Can the EPG shutter move? Is the shutter disc undamaged? Does the shutter disc reach its end positions? Action:

5

“Rocker Arm Shaft Oil Pressure, Checking” page 14 Is the oil pressure within specifications (with activated engine brake)?

Oil pressure in the rocker arm shaft

kPa (psi)

Action: 6

“Rocker Arm Oil Leakage, Checking” page 16 Are the plugs in the rocker arm shaft properly installed? Are the rocker arm shaft’s bolts correctly torque-tightened? Action:

7

“Solenoid/Control Vave, VCB, Checking” page 18 Are the draining hole and draining passage free from debris? Does the solenoid valve open properly? Are the seals free from defects? Action:

8

“Rocker Arm Bushings, Checking” page 16 Rocker arm bushing VCB Are clearances within specifications? Bushing rocker arm roller VCB Are clearances within specifications? Is the clearance between the rocker arm piston and valve bridge within specifications? Action:

9

“Rocker Arm Valve, VCB, Checking” page 20 Are the spring and the non-return valve’s piston free from defects? Does the non-return valve’s piston move freely? Are the non-return valve’s ball and spring free from defects? Does the rocker arm piston move freely? Action:

Notes:

Completed by:

Dealer:

11(21)

Date:

No


Date

2531-20-03-01 Engine Brake, Fault Tracing

3.2003

Group

No.

253

21

Page

2

See also:

• •

“General Guide to Fault Tracing” page 2 “Checklist O, Engine Brake” page 10

Fault Codes, Checking 1 Correct any fault codes concerning the engine brake function; refer to Diagnostic Information, group 20.

Air Supply to EPG and AVU, Checking Special tools: 9992976, 9996465, 9998333 AVU

T2019381

Connect pressure gauge 9996465 and nipple 9992976 to the air supply hose of the AVU.

1

WARNING

9992976

Before beginning any work on any part of the air system, be certain that the air pressure has been depleted. Failure to do so may cause a component to violently separate, which can result in serious personal injury. Remove the air supply hose from the AVU. Remove the fitting in the AVU and attach to test nipple 9992976.

3 Fill the compressed air system to full system air — approximately 8.3 bar (120 psi). If the pressure to control the AVU is not the same as the system pressure, check the air hoses; see “Hoses and Connections” page 12.

Hoses and Connections 4 Check that the air hoses are free of kinks and that they are not damaged or have any restrictions that would interrupt air flow. 5 Check that the hoses are properly connected and do not leak. 6 Empty the compressed air system and remove gauge and test nipple. Remove fitting from test nipple and install fitting into AVU and connect supply hose.

9992976 9996465

12(21)


Date

3.2003

Group

253

No.

21

Page

EPG

Shutter Travel, EPG, Checking

7

1 Check that the system air pressure is more than 7.5 bar (110 psi).

13(21)

2 Remove the exhaust pipe by the EPG and check that shutter disc is not damaged. 3 Connect the PC tool to the vehicle’s data link connector, if this has not already been done.

T2019382

Check that the EPG receives the correct control pressure: remove the air hose from the EPG and connect pressure gauge 9996465 and nipple 9998333 to the hose.

9996465 9998333

4 Using VCADS Pro, begin “Start and heat retention function, test”; activate EPG at 30% (corresponds to the same air pressure as with warm-hold function) and at 100 % (corresponds to full control pressure, exhaust brake). 5

8 Connect the PC tool to the vehicle’s data link connector, if this has not already been done. 9 Using VCADS Pro, run the “Engine brake function test.”

Activate the EPG 10 Activate the AVU for the EPG at 100%. Note the pressure on the checklist. NOTE: The control pressure should be approximately 7.5 ± 0.3 bar (110 ± 4 psi).

W2003781

WARNING 11 If the control pressure is not within specifications and the supply pressure to the AVU is the same as the system air pressure — approximately 8.3 bar (120 psi) — replace the AVU. 12 Remove the gauge and test nipple. Connect air hose to EPG.

EPG shutter may move without warning. Keep hands away from EPG shutter during activation. Failure to do so can result in personal injury. Check that the shutter reaches its end positions by activating and shutting off the EPG using the PC tool. NOTE: The stroke travel (A) should be 29 – 33 mm (1.15 – 1.30 in.).


Date

6 If stroke travel is not within specifications, replace or overhaul EPG; refer to Service Information, group 25.

3.2003

Group

253

No.

Page

21

3

Rocker Arm Shaft Oil Pressure, Checking Special tools: 9998338, 9998339, J39200 1

CAUTION Use a hand wrench to loosen the valve cover nuts; this will help prevent the studs from loosening from the cylinder head and thus damaging the valve cover and the unit injector’s wiring harness. DO NOT USE AN AIR TOOL. Remove the valve cover; refer to Service Information, group 21.

W2004198

Install adapter 9998338 and bolt. NOTE: Attach oil pressure hose. Make sure that adapter and hose remain clear of the no. 1 intake valve rocker arm as the bolt is tightened to 54 Nm (40 ft-lb).

2

4 Temporarily remove the hose. 5 Remove the second stud (counting from left front of engine) so hose can be routed through valve cover.

W2004197

Remove the second bolt on the rocker arm shaft (as viewed from the front of the engine).

6 Route the oil pressure hose from outside and in through the valve cover where the stud was removed.

9998338

14(21)


Date

7

3.2003

W2004199

•

Connect the hose to the banjo nipple on the adapter 9998338.

Connect pressure transducer 9998496 to hose.

2

Attach pressure transducer to multimeter J2900.

3

Select mV setting on multimeter (reading is displayed in kPa).

15(21)

9998496 J39200 9998339

Alternate 2: Connect pressure gauge 9998339.

20 ± 2 Nm (15 ± 1.5 ft-lb)

Oil pressure, VCB activated: 200 - 400 kPa (30 – 60 psi). Oil pressure, VCB non-activated: 100 kPa (15 psi).

15 Repeat test several times to verify reading.

• •

W2004200

12 Lower the hood.

1

Page

14 Test drive the vehicle and bring to operating temperature. Activate VCB and note pressure after it stabilizes.

10

11 Route and secure the oil pressure hose so that it will not be damaged when the hood is closed.

21

Alternate 1:

1

8 Secure the hose so that it will not be damaged by the rocker arms.

Press the seal for the oil pressure hose into the hole on the valve cover.

253

No.

13 Carefully route the hose into the cab.

•

9 Check that the oil pressure hose is correctly positioned and carefully replace the valve cover. Torque-tighten the valve cover to 20 ± 2 Nm (15 ± 1.5 ft-lb).

Group

If oil pressure is below 200 kPa (30 psi) with VCB active, oil pressure is low. Continue fault tracing. If oil pressure is above 100 kPa (15 psi) with VCB inactive and solenoid valve is functioning properly, replace VCB control valve; refer to VCB solenoid valve check.

16 If rocker arm shaft oil pressure is within specifications, remove valve cover and test equipment.

17 Install rocker arm shaft bolt and torque-tighten to 15 ± 5 Nm (11 ± 4 ftlb), then turn additional 120 ± 5 .

15 ± 5 Nm (11 ± 4 ft-lb), 120 ± 5

Volvo Trucks North America, Inc. Service Bulletin 18 Clean valve cover stud and thread hole in cylinder head. Apply locking fluid to stud and torque-tighten to 40 ± 3 Nm (29 ± 2 ft-lb).

Date

40 ± 3 Nm (29 ± 2 ft-lb)

3.2003

Group

253

No.

Page

21

Rocker Arm Bushings, Checking Special tools: 9996956, 9998511, 9999696 Other special equipment: 9989876 Rocker Arm Bushing, VCB 1 Install turning tool 9996956 (or use remote starter switch) to rotate engine. Rotate engine to the position where the rocker arm roller is not in contact with the camshaft cam lobe (base circle).

19 Install valve cover. 20

9996956

NOTE: Check that there is clearance between rocker arm rollers and camshaft for the bushing and roller checks. 2

T2012845

Valve cover tightening sequence

Following the tightening sequence shown, torque-tighten the valve cover to 20 ± 2 Nm (15 ± 1.5 ft-lb).

20 ± 2 Nm (15 ± 1.5 ft-lb)

Rocker Arm Oil Leakage, Checking 1 Check that the plugs in the ends of the rocker arm shafts are properly installed and that they are free from defects. 2 Check all rocker arm bolts in order to make sure that there is no oil leakage due to under-torqued bolts.

16(21)

T2019598

Position magnetic stand 9999696 with dial gauge 9989876 so that the dial gauge’s measurement probe tip is located above the middle of the rocker arm bushing (on the rocker arm not in contact with the camshaft). 3 Move the rocker arm, so that most of the oil film is thinned out on the upper side of the rocker arm shaft. 4 Reset the dial gauge.

9999696 9989876


Date

5

3.2003

Group

253

No.

21

Page

8

C2002679

T2019598

Position bar tool 9998511 under the rocker arm, by the rocker arm shaft, and push up the rocker arm. Note the reading on the dial gauge.

9998511

Max. permitted clearance is 0.1 mm (0.0039 in.). In the case of clearance greater than this, replace the rocker and check the rocker arm shaft for wear. 6 Repeat the check on all other rocker arm bushings.

Place dial indicator 9989876 in magnetic stand 9999696. Put the magnetic stand on the rocker arm. Direct the probe tip of the dial gauge so that it lies horizontally against the center of the roller. Set the dial gauge at 2 – 3 mm (0.080 – 0.118 in.) tension. NOTE: Make sure that the probe tip of the dial gauge is set at tension and can move in both directions. 9

Bushing, Rocker Arm Roller, VCB 7

T2007948 T2007950

Rotate the roller a few turns, so that the oil film between the bushing and shaft is thinned out.

Put a screwdriver between the rocker arm and roller.

NOTE: If the roller jams and does not rotate freely, the rocker arm must be replaced.

Push out the roller as far as possible and read off the value on the dial test indicator.

9999696 9989876

17(21)

Volvo Trucks North America, Inc. Service Bulletin 10

Date

3.2003

Group

253

No.

21

Page

12 Check valve clearance between rocker arm piston and valve bridge. Acceptable clearance is 1.55 – 1.65 mm (0.051 – 0.065 in.); for information on adjusting valves, refer to Service Information, group 21.

Solenoid/Control Vave, VCB, Checking Solenoid valve 1 Remove the solenoid valve from the control valve. 2

T2007951

Using a suitable blunt instrument, push the roller inwards as far as possible. At the same time, note the reading on the dial gauge. If the clearance between the roller and pin is greater than 0.1 mm (0.0039 in.), replace the rocker arm. 11 T2019599

Check that the draining hole is not blocked on the solenoid valve. Also check the draining passage on the control valve.

T2007792

NOTE: When replacing the rocker arm, the new rocker arm bushing should be lubricated with engine oil. Use an oil can and put the tip into the oil passage. Turn the roller while it is being lubricated. Make sure that oil runs out on both sides of the roller.

18(21)


Date

3

3.2003

Group

253

No.

21

Page

19(21)

5 With low oil pressure in the rocker arm shaft, check:

•

The seal between the control valve and the cylinder head.

•

The seals in the pipe between the control valve and the rocker arm shaft.

6

T2019600

Check that the solenoid valve opens and closes properly (battery power [B+] and ground are required to perform this check):

•

With solenoid activated, cover one side of opening and apply low air pressure. The valve should open.

•

With B+ and ground removed, the solenoid valve should close.

•

Replace solenoid valve if it does not open and close properly.

WARNING Wear eye protection. Do not apply full shop air pressure. There is risk of oil splash that can cause personal injury.

Control Valve 4 If the engine oil is very contaminated, remove the control valve and clean it internally.

T2019601

The piston (1) in the control valve is in active position (B), when the solenoid is activated and the oil chamber (2) is drained and the spring presses the piston to its end position. When the engine is switched OFF, there is no oil pressure on either side of the piston, so the piston should be at its end position (via the spring). If the piston jams or sticks, the VCB can become active for a short period after starting. It is highly unlikely that the piston (1) has jammed or stuck in the driving position, i.e. the VCB is not active (A).


Date

3.2003

7 During engine operation, the spring’s force and oil pressure in the oil chamber (2) hold the piston in the balance position which reduces oil pressure.

Group

253

No.

21

Page

20(21)

1

If debris or a foreign object has lodged in the oil chamber (2), this could prevent the piston from returning to its end position, causing the VCB not to function when activated. The control valve must then be disassembled and carefully cleaned or replaced.

Rocker Arm Valve, VCB, Checking T2014923

Turn the engine to top dead center (TDC). The marking for TDC on the camshaft will be between the markings on the forward cap. 2 Heat the plug (1) on VEB rocker cylinder 3 so that the locking fluid ceases to grip. Remove the plug.

Non-return valve 3 Remove the spring (2) and the nonreturn valve piston (3a) and check spring and piston for damage. 4 Place the non-return valve piston (3a) back in the piston bore. Push piston forward and back to verify that piston moves freely in piston bore.

T2019602

5 Check the non-return valve ball (3b) and spring (3c) by pressing the nonreturn valve piston (3a) to end position in order to feel whether there is a spring tension. If no tension is felt, the spring is faulty and should be replaced.

1. Plug 2. Spring 3. Non-return valve 3a. Piston 3b. Ball 3c. Spring

4. Rocker arm piston

Rocker arm piston 6 Push the non-return valve piston (3a) to end position while pressing the rocker arm forward (towards the valves).

Volvo Trucks North America, Inc. Service Bulletin 7 When the rocker arm piston (4) contacts the valve caliper, release the non-return valve piston (3a). 8 Push the rocker arm back (towards the camshaft). Negative pressure will then be created in the rocker arm piston (4). 9 Continue to hold the rocker arm toward the camshaft. Release the negative pressure by pushing in the non-return valve piston (3a). The rocker arm piston (4) should drop toward the valve caliper when negative pressure is released. If piston does not move freely, replace the rocker arm.

Date

3.2003

Group

253

No.

21

10 If no faults were found, install spring (2) and plug (1). NOTE: Apply thread locking fluid to plug before installation. 11 Check the remaining VEB rocker arms: rotate the engine to the next VEB marking and repeat steps 2 – 10.

Page

21(21)

Engine Brake, Fault Tracing

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