UENR0623-02 17 Engine Operation The camshaft has two camshaft lobes for each cylinder. The lobes operate either the inlet valve or the exhaust valve. As the camshaft turns, lobes on the camshaft cause the lifter to move the pushrod up and down. Upward movement of the pushrod against rocker arm results in a downward movement. During reassembly of the rocker shaft the engine must be put into a safe position to avoid engine damage. After load is imposed on the lifters by reassembling the rocker assembly, the engine must be left in safe position for a safe period until the lifters have reduced to the correct length.
Refer to Disassembly and Assembly, “Rocker Shaft and Pushrod - Install” for the correct procedure. This action opens a pair of valves which compresses the valve springs. When the camshaft has rotated to the peak of the lobe, the valves are fully open. When the camshaft rotates further, the two valve springs under compression start to expand. The valve stems are under tension of the springs. The stems are pushed upward. The continued rotation of the camshaft causes the rocker arm, the pushrods and the lifters to move downward until the lifter reaches the bottom of the lobe. The valves are now closed. The cycle is repeated for all the valves on each cylinder.
i05242096 Clean Emissions Module To meet current emissions legislation requirements, a small amount of certain chemical compounds that are emitted by the engine must not be allowed to enter the atmosphere. The Clean Emissions Module (CEM) that is installed to the engine is designed to convert these chemical compounds into less harmful compounds. The rocker arm incorporates a hydraulic lash adjuster which removes valve lash from the valve mechanism. The hydraulic lash adjuster uses engine lubricating oil to compensate for wear of system components so that no service adjustment of valve lash is needed. The Engine Aftertreatment System for the engine consists of the following components.
The engine lubricating oil enters the hydraulic lash adjuster through a non-return valve. The engine lubricating oil increases the length of the hydraulic lash adjuster until all valve lash is removed. If the engine is stationary for a prolonged period the valve springs will cause the hydraulic lash adjuster to shorten so that when the engine is started engine valve lash is present for the first few seconds. Diesel Oxidation Catalyst (DOC) Diesel Particulate Filter (DPF) The Diesel Oxidation Catalyst (DOC) oxidizes the carbon monoxide and the hydrocarbons that are not burnt in the exhaust gas into carbon dioxide and water.
The Diesel Oxidation Catalyst (DOC) is a through flow device that will continue to operate during all normal engine operating conditions. After cranking restores oil pressure the hydraulic lash adjuster increases in length and removes the valve lash. When load is removed from a hydraulic lash adjuster during service work by the removal of the rocker shaft the hydraulic lash adjuster increases in length to the maximum extent. Refer to Systems Operation, Testing and Adjusting, “Position the Valve Mechanism Before Maintenance Procedures” for the correct procedure. The Diesel Particulate Filter (DPF) collects all solid particulate matter in the exhaust gas.
The solid particulate matter that is collected by the DPF consists of soot (carbon) from incomplete combustion of the fuel and inorganic ash from the combustion of any oil in the cylinder.