Hydraulic tappets are installed on the engines, which automatically compensate for the gap between the camshaft cam and the corresponding valve stem under the action of pressure in the lubrication system. Therefore, regular checking and adjustment of valve clearances is not required. However, you must use engine oil of good quality and recommended viscosity and replace it at the required intervals. When starting a cold engine, there is a slight delay due to the equalization of the engine oil pressure in all parts of the engine, especially in the hydraulic tappets. The valves may knock for approximately 10 seconds, after which they begin to operate silently.
If the engine has not been started for several days, the valves may knock for a longer time as almost all of the oil drains from the top of the engine and bearing surfaces. At this time, care must be taken not to damage the engine: avoid sudden changes in engine operation until all pushrods are filled with engine oil. When the engine warms up, the idle speed (maximum 2000 to 2500 min–1) should not rise for 2 minutes or until valve banging stops. If the tappet noise does not stop, stop the engine and do the following: (engine temperature must be at least 80°C).
Remove the cylinder head cover.
Rotate the crankshaft until the cam over the tappet to be checked is straight up.
Pic. 3.1–91. Checking the free travel of the pusher
Press the pusher with a wooden or plastic wedge (pic. 3.1–91). If the pusher play is greater than 0.2 mm, the pushers must be replaced.
Install the cylinder head cover.
Wait approximately 30 minutes before starting the engine. This is necessary in order to stabilize the operation of the hydraulic tappets, otherwise the pistons will hit the valves.
Valve seat processing
Valve seats with signs of wear or burning must be processed with the obligatory preservation of angles and chamfers.
Pic. 3.1–92. Minimum allowable distance from the end face of the valve to the top surface of the cylinder head
If the valve seat needs to be machined, determine the maximum amount of metal that can be removed. If excessive metal is removed, the hydraulic tappets will fail. Insert the valve into the guide sleeve and press it against the valve seat. Measure the distance from the end of the valve stem to the top surface of the cylinder head (pic. 3.1–92). Minimum allowable distance A is 33.8 mm for intake valves and 34.1 mm for exhaust valves. If the valve seat is excessively worn, the cylinder head must be replaced.
After any treatment of the seats, the valves must be lapped.
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