Valve System And Timing Gear
- Camshaft position sensor, intake
- Induction camshaft
- VVT actuator intake camshaft
- VVT unit intake camshaft
- Timing belt
- Gear drive crankshaft
- Mechanical belt tensioner
- VVT-unit exhaust camshaft
- VVT actuator exhaust camshaft
- Exhaust camshaft
- Camshaft position sensor, exhaust
- Cam wheel to vacuum/fuel pump
The valve system on petrol engines in the VEA family is traditionally made up of four valve technology and double camshafts driven by a belt at the front edge of the engine. For a more compact engine design, the camshafts are closer together than on five cylinder petrol engines. This, in turn, gives a slightly steeper valve angle. Both camshafts are fitted with timing gear pulleys with VVT units for variable valve timing. The exhaust camshaft also drives the fuel pump on a separate cam lobe and the vacuum pump with a groove in the rear edge.
Valve system
- Intake camshaft
- Exhaust camshaft
- Valve depressor
- Retainer
- Valve seal
- Exhaust
- Sodium cooling
- Outlet valve
- Valve seat
- Inlet valve
- Inlet
- Valve guide
- Valve spring
- Valve spring washer
Valves
The material of the valves is high-grade steel, similar to that for the five cylinder turbocharged engines. The exhaust valves have sodium cooled valve stems.
The valve guides are manufactured in a material that contains so-called solid lubricant. This makes the valve guides more resistant to wear.
Valve seats
The valve seats are also made of a more high-grade material than used in previous engine variants. The reason is that the fuel in direct injection is sprayed directly onto the piston in the cylinder, which means the intake valve seat gets less lubrication.
Valve seals
To minimize the risk of combustion gases passing between the valve stem and guide, the valve seals have double sealing lips, which act as check valves. In addition to sealing off gases from the combustion chamber, the seal must also allow oil through to lubricate the valve stem. The exhaust valves need more lubrication compared to the intake valves. The valve seals are therefore available in two variants. The seals on the inlet valves are brown. The seals on the exhaust valves are green.
Valve depressor
The petrol engines have fixed tappets the same size as on five cylinder petrol engines. At valve adjustment the same range of tappets can be used as for these engines. The tappets have DLC as an anti-slip coating. Valve clearance:
- Intake: 0.2 mm
- Exhaust: 0.52 mm
Camshafts
For petrol engines in the VEA family, cast camshafts are used. To minimize the friction and the width of the engine a roller bearing is used at the first bearing position.
- VVT unit
- P box
- Roller bearing
- Snap-ring
- Sleeve
VVT seal
The VVT rings are sealed by means of a loose aluminum sleeve instead of directly in the cylinder head as before.
Two guide lugs position the sleeve correctly with the hole upwards.
Exhaust camshaft
At the rear end of the camshaft there is a cam wheel that drives the high pressure fuel pump. There is a milled groove at the far end. The groove is not only used to reset the camshafts with a tool, it is also intended to drive the vacuum pump.
The groove is hardened, which makes it very important not to use the reset tool as a counterhold when torque tightening the VVT unit. Instead always use counterhold tool 999 7497 when tightening.
VVT unit (Variable Valve Timing)
Both the intake and exhaust camshafts have adjustable opening times using the hydraulically controlled VVT units. Function and structure is similar to VVT units from five cylinder petrol engine, B5254T12. The intake camshaft VVT unit is adjusted within a range of approximately 50 crankshaft degrees. The exhaust camshaft approximately 30°. Without oil pressure, the VVT unit is locked. The clearance in the locked position is approx. 1.5 crankshaft degrees.
| Lift height (mm) | Opening time (duration) | Opens | Closes |
| All | 8.57° - 227° | 35.5° BTDC - 14.5° ATDC | 191.5° ATDC - 241.5° ATDC |
| Lift height (mm) | Duration | Opens | Closes |
| Engine B4204T9, T10 | 8, 465 - 224° | 218° BTDC - 188° BTDC | 6° ATDC - 36° ATDC |
| Engine B4204T11, T12, T15 | 7, 865 - 215° | 209° BTDC - 179° BTDC | 6° ATDC - 36° ATDC |
Opening angles given at 1 mm valve opening. BTDC (Before Top Dead Centre), ATDC (After Top Dead Centre)
There is a friction washer with a diamond coating between the VVT unit and the camshaft. Read more about diamond washers under the heading Crank system.
VVT solenoid (Variable Valve Timing)
Via the solenoid the engine control module (ECM) controls the position of the camshaft hydraulically. Regulation is via a 12V PWM signal.
Timing belt, Engine B4204T9/T10/T12/T13/T15
The camshafts' timing belt is traditionally located at the front edge of the engine. The crankshaft drives the belt (23 mm in width) via a gear drive, which is connected to both camshafts. The belt is tensioned using a mechanical belt tensioner. The replacement interval for the timing belt including tensioner and idler wheel is 240 000 km.
Gear drive
The crankshaft's gear drive is slightly oval, which partly must counteract the pulse frequency that is generated in the timing belt. The ovality is approx. 1 mm.
Timing belt tension
As the belt tensioner for these engines has a narrow sprung movement (to prevent skipping a tooth) with a relatively short toothed belt, it is important that belt tension is checked when the engine is at room temperature (20-25 °C). If this is not done, there a is a great risk that the tensioner will work towards an end position when the engine is at operating temperature resulting in tensioner failure.
Should the engine be too cold during adjustment, there is a risk that the belt is over-tensioned and the tensioner works toward the upper end position.
Should the engine be too hot during adjustment, there is a risk that the belt is too slack and the tensioner works toward the lower end position.
During belt replacement, the crankshaft must be rotated at least two turns before the belt tension is adjusted. This is so that the belt will assume the correct position (for both depth and width). The belt tensioner indicator is difficult to read due to lack of space. It may be useful to use a mirror when reading out and to raise/lower the engine's timing gear side.
Belt guard
Engines B4204T9/T10/T12/T13/T15 have a belt guard to protect the timing belt from external influences such as stones, water etc. The guard also provides some protection against an incorrectly installed or defective Accessory Drive Belt where on other engine options this can cause the Accessory Drive Belt to end up in the timing gear resulting in engine failure.
Accessory drive Engine B4204 T9, T10
- Camshafts
- Runner
- Alternator
- air conditioning (A/C) compressor.
- Crankshaft gear/Vibration damper
- Automatic belt tensioner for accessory drive belt.
- Compressor
The accessory drive component is located on the front of the engine and consists of an alternator (3), an A/C compressor (4), and a boost compressor (7). The accessory drive component is driven via the crankshaft by a multi-rib belt that is tensioned using a mechanical belt tensioner (6). Even the vibration damper on these engine variants has an integrated releaser that takes up the engine's pulsations to the belt, where the alternator does not have a freewheel function. The multi belt, including tensioner and idler wheel (2), must be replaced at an interval of 240 000 km.
Belt tensioner
- Wrench
- Pin/drill bit
The tensioner is released by means of a 15 mm wrench (1) on screw (left-threaded) for the tensioner's idler wheel. The belt tensioner has an integrated damper and can be held compressed (facilitates belt replacement) using a 3 mm pin/drill bit (2).
Accessory Drive Belt, B4204T12/T13/T15 as well as D4205T5
The accessory drive component is located on the front of the engine and consists of an alternator and an A/C compressor.
The accessory drive component is driven via the crankshaft by a multi-rib belt that is tensioned using a mechanical belt tensioner. Since the crankshaft's vibration damper has an integrated releaser that takes up the engine's pulsations to the belt, the alternator does not have a freewheel function. The multi-rib belt's replacement interval, including tensioner and idler wheel, is 240 000 km.
Belt tensioner
The belt tensioner has an integrated damper and can be held compressed (facilitates belt replacement) using a 3-4 mm pin/drill bit.