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| Illustration 1 | g02428457 |
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Valve system components (1) Valve spring (2) Rotocoil (3) Valve bridge assembly (4) Rocker arm (5) Rocker shaft assembly (6) Hydraulic lash adjuster (7) Valve lifter (8) Camshaft (9) Camshaft lobes | |
Camshaft (8) is rotated through the rear gear train by the crankshaft. The rotation of camshaft is precisely timed to the rotation of the crankshaft. This timing ensures that the correct relation between the movement of the piston and the movement of the valves is maintained.
Two lobes (9) are machined into the camshaft for each cylinder. One lobe operates the valve mechanism components for the inlet valves and the other lobe operates the valve mechanism components for the exhaust valves.
As the camshaft rotates, the rollers on valve lifters (7) travel up the camshaft lobes. Hydraulic lash adjuster (HLA) (6) transfers this motion to rocker arm (4). The rocker arms pivot on rocker shaft assemblies (5). The rocker arms act as a lever as the motion is transferred to the top of valve bridge assembly (3). The valve bridge assemblies transfer movement from the rocker arms to the top of the valve stems. The bridge assemblies operate two valves simultaneously. There is a pair of intake valves and a pair of exhaust valves for each cylinder.
Within the HLA, there is a low-pressure chamber and a high-pressure chamber. The high-pressure chamber carries the load during operation. The low-pressure chamber provides oil to the high-pressure chamber during starting and service.
The low-pressure chamber has 3 times the volume of the high-pressure chamber. During service, the high-pressure chamber bleeds down when the HLA is on the ramp of the cam (without engine running). Therefore, the low-pressure chamber will need to refill the high-pressure chamber when the cam returns to the base circle. The low-pressure chamber can refill the high-pressure chamber approximately 3 times when the cam returns to the base circle.
Once the low-pressure chamber is empty, the HLA will not be able to recover the high-pressure chamber (feel firm), until the low-pressure chamber is refilled. Refer to Testing and Adjusting, “Valve Lash - Adjust (Hydraulic Lash Adjusters)” for the adjustment procedure to refill the HLA and readjust.
Rotocoils (2) initiate a rotational movement to the valves as the valves are opened and closed. The rotation of the valves keeps the carbon deposits on the valves to a minimum which gives the valves a longer service life.
Valve springs (1) are used to provide a spring tension force on the valves. This force causes the valves to close as the lifters travel off the camshaft lobe.