Engine Brake, Fault Tracing

8/13/2019 Engine Brake, Fault Tracing

1/21

Service BulletinVolvo Trucks North America, Inc.Greensboro, NC USA

Date Group No. Pa

3.2003 253 21 1(2

TrucksThis Service Bulletin replaces SB 25321, EngineBrake, Fault Tracing, Checklist O, D12D (11.02), publi-cation no. PV776TSP170589.

Engine Brak

Fault Tracin

Checklist

D12

Engine Brake, Fault Tracing

Checklist O

T2019344

This information covers fault tracing the VEB (Volvo Engine Brake) for the Volvo D12Dengine.

Contents General Guide to Fault Tracing page 2

System Overview page 3

Checklist O, Engine Brake page 10

Engine Brake, Fault Tracing page 12

NOTE: Information is subject to change without notice.

Illustrations are used for reference only, and may differ slightly from the actualengine version. However, key components addressed in this information are repre-sented as accurately as possible.

PV776-TSP187872 USA132


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Volvo Trucks North America, Inc. Date Group No. Page

Service Bulletin 3.2003 253 21 2(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 Informa-tion, group 20, "General Safety Practices, Engine" before performing any procedure.If you are not properly trained and certified in a procedure, ask your supervisor fortraining before you perform it.

To use this checklist:

1 Complete basic data gathering Read fault codes

Check vehicle parameters

2 Use the recommendations in appropriate symptom information, plus the infor-mation gathered above to provide a foundation for continued fault tracing usingthis checklist.

One fault often affects other systems. Therefore, it is important to confirm oreliminate suspected causes of faults at an early stage, using tests in VCADSPro.


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Volvo Trucks North America, Inc. Date Group No. Pa

Service Bulletin 3.2003 253 21 3(2

System Overview

W2004194

When fault tracing, it is important to understand the function of the system andto follow the fault tracing sequence in the checklist to avoid replacing non-defective components.


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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)


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Engine Brake

For additional information on the design and functionof the Volvo Engine Brake, refer to Service Informa-tion, group 25.

There are two options for engine braking:

Exhaust brake, EPGThe exhaust pressure governor (EPG) uses a shuttermounted in the exhaust outlet from the turbocharger.This shutter, connected to the EPG plunger, can restrictthe exhaust gas flow. This creates a braking effect dur-ing the exhaust stroke when the exhaust gases cannotevacuate freely; they create an overpressure betweenthe pistons and the shutter.

For a more detailed description of the EPG function, seeExhaust Pressure Governor (EPG) page 7.

Engine brake, VEBThe 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, mak-ing the compression brake more efficient.

The VEB includes a special rocker arm for the exhaustvalves, a special camshaft with extra cams and a sole-noid valve for oil pressure in the rocker arm. For a moredetailed technical description, see Compression Brakepage 8.

The braking effect of the compression brake on the en-

gine occurs when:

The exhaust valve opens and allows air induringthe intake stroke, which gives more air to compressduring the compression stroke.

The exhaust valve opens immediately before theturn of the compression strokeand punctures thecompression in order to reduce the effect with theworking stroke.

Electrical control of engine brakeThe engine brake power is determined by the driverssettings. The power varies for different combinations ofengine brakes.

EPG

Switch (S07)

T0008637

Two positions.

The position of theswitch

Engine brake

0 (switched off) 0 %

1 100 %

Electrical controlWith the switch in position 1, the exhaust brake is acti-vated when the accelerator (B25) is released.

The information from the switch and the accelerator govia 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 sign(Pulse Wide Modulated) to the AVU (Y37), which sendout full control pressure (7.5 bar/110 psi) to the EPG.

The AVU is given voltage via fuse F80.

Requirements Clutch pedal (S58) is NOT depressed. Engine speed exceeds 900 rpm; engine speed se

sor, B04 (deactivates < 800 rpm).

Speedometer (B68) indicates a speed greater tha5 km/h (3 mph).

ABS wheel sensor (B13-18) indicates NO wheellockup (ABS non-active).


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VEB

Switch (S07)

T0008058

Three positions.

The position of theswitch

Engine brake

0 (switched off) 0 %

1 50 %

2 100 %

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

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

The information from the switch and the accelerator govia the vehicle control unit (A17) through the data links(J1939 and J1708/J1587) to the engine ECU (A14). Theengine ECU then sends a signal (-) to the sole-noid/control valve (Y39) for increased oil pressure in therocker arm shaft and a PWM signal (Pulse Wide Modu-lated) to the AVU (Y37). Both the control valves aresupplied voltage via fuse F80.

Requirements 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 than5 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 wheellockup (ABS non-active).

NOTE:*Activation rpm is raised by 300 to 1400 rpm

when oil temperature is 55 82

C (131 180

F) or af-ter the first 5 engine brake requests.


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Exhaust Pressure Governor (EPG)

W2004195

The exhaust pressure governor has three functions:

To keep the engine warm when idling.

To function as exhaust brake on down gradients.

To apply exhaust back pressure during idle EGRfunction.

The exhaust pressure governor is situated in direct con-nection to the turbos turbine housing. The exhaust

pressure governor consists of a shutter housing(1), ashutter(2) and a compressed air operated cylinder (3).The compressed air is supplied from the vehicles com-pressed air system and is regulated by the AVU, locatedon the intake side of the engine (4), and releases a re-duced pressure to the exhaust pressure governor. ThePWM-type valve controls the pressure steplessly within0.5 7.5 bar (7 - 110 psi).

Under normal driving conditions, the AVU (4) is closed.The shutter (2) is then completely open and the exhaustpasses freely.

Start and heat retentionFor functional description and fault tracing of the exhaupressure governor during start and heat retention, refeto Service Information, group 25, EPG, Fault Tracing,Checklist E.

Exhaust brakeThe EPG is activated by control pressure of approxi-mately 7.5 bar (110 psi). The shutter (2) is forced intothe shutter housing (1) which restricts exhaust flow and

causes back pressure in the exhaust.

If the engine is equipped with VEB (Volvo Engine Brakethe compression brake and EPG are activated simulta-neously to attain 100% engine brake (switch position 2


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Compression Brake

Solenoid/Control Valve

T2019494

The solenoid/control valve has the task of regulating theoil pressure to the rocker arm mechanism.

The inlet (1), which is connected to the lubricating oilpassage in the cylinder block, always has system oilpressure. The outlet (5) is connected to the rocker armshaft. The compression brake is activated by the sole-noid valve (2), which is controlled from the EECU.

A: When the engine is running the piston (3) partlycovers the outlet (5), which results in reduction of oilpressure to approximately 100 kPa (14.5 psi) after thesolenoid valve. This oil pressure is sufficient for lubrica-tion of the camshaft bearings and the rocker armmechanism.

B: With compression braking, voltage to the solenoidvalve(2) opens a draining passage. The oil in the oilspace (6) flows out through the draining passage, allow-ing the spring (4) to push the piston (3) to the side. Thismeans the outlet (5) becomes free and the oil pressurefrom the gallery connection provides the rocker arm shaftwith full oil pressure more than 200 kPa (29 psi).


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Camshaft and exhaust rocker arms

W2004

The camshaft (1) on an engine with VCB has, in additionto the ordinary exhaust cam (2), a charge cam(3) and adecompression cam(4) on each exhaust cam lobe.

Each rocker arm (5) includes a non-return valve(7) anda rocker arm piston (8). A spring tab(6) holds the rockerarm in its resting position against the valve bridge. Thenon-return valve clearance is adjusted with the help ofshim(9) which is situated on the valve bridge.

The non-return valve (7) consists of a piston (11) andspring (14), spring (12) and ball (13).

A: Under normal engine operation, the sole-noid/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 oilpressure is not sufficient to overcome the spring force(14). The pistons pin holds the ball (13)away from theseat, which allows the oil to flow in both directionsthrough the non-return valve. This prevents excess oilpressure building up above the rocker arm piston (8).

In this position the exhaust valves are not affected by theextra brake cams on the camshaft.

B: With compression braking, the solenoid/controlvalve 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 ba(13)towards the seat. The oil, above the rocker arm piton(8), can no longer flow past the ball and thereforepushes on the rocker arm piston (8), so that the pistonpushes down and eliminates the valve clearance.

When the camshafts extra brake cams (3) and (4) fur-ther affect movement of the rocker arm, the exhaustvalves are pushed down and compress (force more airinto the cylinder with the help of the back pressure in thexhaust during the compression stroke) and decompresion respectively (release compression during the powstroke).

So that the pressure above the rocker arm piston doesnot push back into the rocker arm shaft when the valveopens, there is a pressure limiting valve (10).


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Checklist O, Engine BrakeSee also:

General Guide to Fault Tracing page 2 Engine Brake, Fault Tracing page 12

Vehicle Mileage CustomerChassis no.Yes No

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) bar (psi)

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:


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Vehicle Mileage CustomerChassis no.Yes No

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 shafts 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 valves piston free from defects?

Does the non-return valves piston move freely?

Are the non-return valves ball and spring free from defects?

Does the rocker arm piston move freely?

Action:

Notes:

Completed by: Dealer: Date:


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2531-20-03-01Engine Brake, Fault TracingSee also:

General Guide to Fault Tracing page 2

Checklist O, Engine Brake page 10

Fault Codes, Checking1Correct any fault codes concerning theengine brake function; refer to Diag-nostic Information, group 20.

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

AVU

1

WARNING

Before beginning any work on any part of the airsystem, be certain that the air pressure has beendepleted. Failure to do so may cause a componentto violently separate, which can result in serious per-sonal injury.

Remove the air supply hose from theAVU. Remove the fitting in the AVUand attach to test nipple 9992976.

9992976

2

T2019381

Connect pressure gauge 9996465 andnipple 9992976 to the air supply hoseof the AVU.

3Fill the compressed air system to fullsystem air approximately 8.3 bar(120 psi).

If the pressure to control the AVU isnot the same as the system pressure,check the air hoses; see Hoses and

Connections page 12.

99929769996465

Hoses and Connections

4Check that the air hoses are free ofkinks and that they are not damagedor have any restrictions that would in-terrupt air flow.

5Check that the hoses are properly

connected and do not leak.

6Empty the compressed air system andremove gauge and test nipple. Re-move fitting from test nipple and installfitting into AVU and connect supplyhose.


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EPG

7

T2019382

Check that the EPG receives the cor-rect control pressure: remove the airhose from the EPG and connect pres-sure gauge 9996465 and nipple9998333 to the hose.

99964659998333

8Connect the PC tool to the vehiclesdata link connector, if this has not al-ready been done.

9Using VCADS Pro, run the Enginebrake function test.

Activate the EPG

10Activate the AVU for the EPG at 100%.Note the pressure on the checklist.

NOTE:The control pressure should beapproximately 7.5 0.3 bar (110 4

psi).

11If the control pressure is not withinspecifications and the supply pressureto the AVU is the same as the systemair pressure approximately 8.3 bar(120 psi) replace the AVU.

12Remove the gauge and test nipple.Connect air hose to EPG.

Shutter Travel, EPG, Checking

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

2Remove the exhaust pipe by the EPGand check that shutter disc is not dam-aged.

3Connect the PC tool to the vehiclesdata link connector, if this has not al-ready been done.

4Using VCADS Pro, begin Start and

heat retention function, test; activateEPG at 30% (corresponds to the sameair pressure as with warm-hold func-tion) and at 100 % (corresponds to fullcontrol pressure, exhaust brake).

5

W2003781

WARNING

EPG shutter may move without warning. Keep handsaway from EPG shutter during activation. Failure todo so can result in personal injury.

Check that the shutter reaches its endpositions by activating and shutting offthe EPG using the PC tool.

NOTE:The stroke travel (A) should be29 33 mm (1.15 1.30 in.).


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6If stroke travel is not within specifica-tions, replace or overhaul EPG; referto Service Information, group 25.

Rocker Arm Shaft Oil Pressure,CheckingSpecial tools: 9998338, 9998339, J39200

1

CAUTION

Use a hand wrench to loosen the valve cover nuts;this will help prevent the studs from loosening fromthe cylinder head and thus damaging the valve coverand the unit injectors wiring harness. DO NOT USEAN AIR TOOL.

Remove the valve cover; refer to Ser-vice Information, group 21.

2

W2004197

Remove the second bolt on the rockerarm shaft (as viewed from the front ofthe engine).

3

W2004198

Install adapter 9998338 and bolt.

NOTE:Attach oil pressure hose. Makesure that adapter and hose remainclear of the no. 1 intake valve rockerarm as the bolt is tightened to 54 Nm(40 ft-lb).

9998338

4Temporarily remove the hose.

5Remove the second stud (countingfrom left front of engine) so hose canbe routed through valve cover.

6Route the oil pressure hose from out-side and in through the valve coverwhere the stud was removed.


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7

W2004199

Connect the hose to the banjo nippleon the adapter 9998338.

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

9Check that the oil pressure hose iscorrectly positioned and carefully re-place the valve cover. Torque-tightenthe valve cover to 20 2 Nm (15 1.5ft-lb).

20 2 Nm(15 1.5 ft-lb)

10

W2004200

Press the seal for the oil pressurehose into the hole on the valve cover.

11Route and secure the oil pressurehose so that it will not be damagedwhen the hood is closed.

12Lower the hood.

13Carefully route the hose into the cab.

Alternate 1:

1 Connect pressure transducer

9998496 to hose.

2 Attach pressure transducer tomultimeter J2900.

3 Select mV setting on multi-meter (reading is displayed inkPa).

Alternate 2:

1 Connect pressure gauge9998339.

9998496J392009998339

14Test drive the vehicle and bring to op-erating temperature. Activate VCB andnote pressure after it stabilizes.

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

Oil pressure, VCB non-activated: 100kPa (15 psi).

15Repeat test several times to verifyreading.

If oil pressure is below 200 kPa(30 psi) with VCB active, oil pres-sure is low. Continue fault tracing.

If oil pressure is above 100 kPa(15 psi) with VCB inactive andsolenoid valve is functioning prop-erly, replace VCB control valve;refer to VCB solenoid valve check.

16If rocker arm shaft oil pressure iswithin specifications, remove valvecover and test equipment.

17Install rocker arm shaft bolt andtorque-tighten to 15 5 Nm (11 4 ft-lb), then turn additional 120 5

.

15 5 Nm(11 4 ft-lb)120 5


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18Clean valve cover stud and threadhole in cylinder head. Apply lockingfluid to stud and torque-tighten to 40 3 Nm (29 2 ft-lb).

40 3 Nm(29 2 ft-lb)

19Install valve cover.

20

T2012845

Valve cover tightening sequence

Following the tightening sequenceshown, torque-tighten the valve coverto 20 2 Nm (15 1.5 ft-lb).

20 2 Nm(15 1.5 ft-lb)

Rocker Arm Oil Leakage, Check-ing

1Check that the plugs in the ends of therocker arm shafts are properly installedand that they are free from defects.

2Check all rocker arm bolts in order tomake sure that there is no oil leakagedue to under-torqued bolts.

Rocker Arm Bushings, CheckingSpecial tools: 9996956, 9998511, 9999696Other special equipment: 9989876

Rocker Arm Bushing, VCB

1Install turning tool 9996956 (or use re-mote starter switch) to rotate engine.Rotate engine to the position wherethe rocker arm roller is not in contactwith the camshaft cam lobe (base cir-cle).

NOTE:Check that there is clearancebetween rocker arm rollers andcamshaft for the bushing and rollerchecks.

9996956

2

T2019598

Position magnetic stand 9999696 withdial gauge 9989876 so that the dialgauges measurement probe tip is lo-catedabove the middle of the rockerarm bushing (on the rocker arm not incontact with the camshaft).

99996969989876

3Move the rocker arm, so that most ofthe oil film is thinned out on the upperside of the rocker arm shaft.

4Reset the dial gauge.


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5

T2019598

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

Max. permitted clearance is 0.1 mm(0.0039 in.). In the case of clearancegreater than this, replace the rockerand check the rocker arm shaft forwear.

9998511

6Repeat the check on all other rockerarm bushings.

Bushing, Rocker Arm Roller, VCB

7

T2007948

Rotate the roller a few turns, so thatthe oil film between the bushing andshaft is thinned out.

NOTE:If the roller jams and does notrotate freely, the rocker arm must bereplaced.

8

C2002679

Place dial indicator 9989876 in mag-netic stand 9999696. Put the magneticstand on the rocker arm.

Direct the probe tip of the dial gaugeso that it lies horizontally against thecenter of the roller.Set the dial gauge at 2 3 mm (0.080

0.118 in.) tension.

NOTE:Make sure that the probe tip ofthe dial gauge is set at tension and

can move in both directions.

99996969989876

9

T2007950

Put a screwdriver between the rockerarm and roller.

Push out the roller as far as possibleand read off the value on the dial testindicator.


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10

T2007951

Using a suitable blunt instrument,push the roller inwards as far as possi-ble. At the same time, note thereading on the dial gauge.

If the clearance between the roller andpin is greater than 0.1 mm (0.0039in.), replace the rocker arm.

11

T2007792

NOTE:When replacing the rockerarm, the new rocker arm bushingshould be lubricated with engine oil.Use an oil can and put the tip into theoil passage. Turn the roller while it isbeing lubricated. Make sure that oilruns out on both sides of the roller.

12Check valve clearance between rockerarm piston and valve bridge. Accept-able clearance is 1.55 1.65 mm(0.051 0.065 in.); for information onadjusting valves, refer to Service Infor-mation, group 21.

Solenoid/Control Vave, VCB,Checking

Solenoid valve

1Remove the solenoid valve from thecontrol valve.

2

T2019599

Check that the draining hole is notblocked on the solenoid valve. Alsocheck the draining passage on thecontrol valve.


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3

T2019600

Check that the solenoid valve opensand closes properly (battery power[B+] and ground are required to per-form this check):

With solenoid activated, cover oneside of opening and apply low airpressure. The valve should open.

With B+ and ground removed, thesolenoid valve should close.

Replace solenoid valve if it doesnot open and close properly.

WARNING

Wear eye protection. Do not apply full shop air pres-sure. There is risk of oil splash that can causepersonal injury.

Control Valve

4If the engine oil is very contaminated,remove the control valve and clean itinternally.

5With low oil pressure in the rocker armshaft, check:

The seal between the controlvalve and the cylinder head.

The seals in the pipe between thecontrol valve and the rocker armshaft.

6

T2019

The piston (1) in the control valve is inactive position (B), when the solenoidis activated and the oil chamber (2) isdrained and the spring presses thepiston to its end position.

When the engine is switched OFF,there is no oil pressure on either sideof the piston, so the piston should beat its end position (via the spring). Ifthe piston jams or sticks, the VCB canbecome active for a short period afterstarting.

It is highly unlikely that the piston (1)has jammed or stuck in the driving po-sition, i.e. the VCB is not active (A).


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7During engine operation, the springsforce and oil pressure in the oil cham-ber (2) hold the piston in the balanceposition which reduces oil pressure.

If debris or a foreign object has lodged

in the oil chamber (2), this could pre-vent the piston from returning to itsend position, causing the VCB not tofunction when activated. The controlvalve must then be disassembled andcarefully cleaned or replaced.

Rocker Arm Valve, VCB, Check-ing

T2019602

1. Plug

2. Spring

3. Non-return valve3a. Piston

3b. Ball

3c. Spring

4. Rocker arm piston

1

T2014923

Turn the engine to top dead center

(TDC). The marking for TDC on thecamshaft will be between the markingson the forward cap.

2Heat the plug (1) on VEB rocker cylin-der 3 so that the locking fluid ceasesto grip. Remove the plug.

Non-return valve

3

Remove the spring (2) and the non-return valve piston (3a) and checkspring and piston for damage.

4Place the non-return valve piston (3a)back in the piston bore. Push pistonforward and back to verify that pistonmoves freely in piston bore.

5Check the non-return valve ball (3b)and spring (3c) by pressing the non-

return valve piston (3a) to end positionin order to feel whether there is aspring tension. If no tension is felt, thespring is faulty and should be replaced.

Rocker arm piston

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


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7When the rocker arm piston (4) con-tacts the valve caliper, release thenon-return valve piston (3a).

8Push the rocker arm back (towards thecamshaft). Negative pressure will thenbe created in the rocker arm piston (4).

9Continue to hold the rocker armtoward the camshaft. Release the neg-ative pressure by pushing in thenon-return valve piston (3a). Therocker arm piston (4) should drop to-ward the valve caliper when negativepressure is released. If piston does notmove freely, replace the rocker arm.

10If no faults were found, install spring(2) and plug (1).

NOTE:Apply thread locking fluid toplug before installation.

11Check the remaining VEB rockerarms: rotate the engine to the nextVEB marking and repeat steps 2 10.

Documents

Engine Brake, Fault Tracing