The hydraulic compensators of the F16D and F18D engines, made in the form of cylindrical tappets located between the camshaft and the valves, combine two functions: transmitting force from the camshaft to the valves and eliminating gaps in their drive.
The operation of the hydraulic compensator is based on the principle of incompressibility of engine oil, which constantly fills the internal cavity of the hydraulic compensator during engine operation and moves its plunger when a gap appears in the valve drive. This ensures constant contact of the pusher (valve drive lever) with a camshaft cam without clearance. Due to this, there is no need to adjust the valves during maintenance. The operating principle of the hydraulic compensator is shown in Fig. 5.8. Oil under the pressure required for the operation of the hydraulic compensator is supplied to its internal cavities A and B from channel B of the engine lubrication system through a side hole in tappet 6, made in the annular groove of its cylindrical surface. When valve 1 is closed, tappet 6 (through plunger 7) and the sleeve 9 are pressed by the expanding force of the spring 8 respectively to the cam 5 of the camshaft and the end of the valve stem. The pressure in cavities A and B is the same, the check valve 3 of the hydraulic compensator is pressed to the seat in the plunger 7 by the spring 2. In this case, there are no gaps in the valve mechanism. When the camshaft rotates, cam 5 runs onto tappet 6, moving it and the plunger 7 connected to it. The movement of plunger 7 in sleeve 9 leads to a sharp increase in pressure in cavity B. Despite small oil leaks through the gap between the plunger and the sleeve, tappet 6 and sleeve 9 move as a single unit and open valve 1. With further rotation of the camshaft, cam 5 reduces the pressure on tappet 6 and the oil pressure in cavity B becomes lower than in cavity A. Check valve 3 opens and passes oil from cavity A, connected to the engine oil line, into cavity B. The pressure in cavity B increases, sleeve 9 and plunger 7, moving relative to each other, select the gap in the valve mechanism.
Fig. 5.8. Operation diagram of the hydraulic valve clearance compensator: a - operation of the hydraulic compensator at the moment of opening the valve; b - operation of the hydraulic compensator at the moment of valve closing; 1 - valve; 2 - check valve spring; 3 - check valve; 4 - cylinder head; 5 - camshaft cam; b - pusher; 7 - plunger; 8 - plunger spring; 9 - sleeve; 10 - check valve body; A, B - cavities of the hydraulic compensator; B - oil channel
The pressure of the oil supplied to the hydraulic compensators is regulated by a special valve installed in the cylinder head. Since after stopping the engine, oil flows from the channels coming from the oil pump into the oil sump, and the channels supplying oil to the hydraulic compensators remain filled, air locks may form in the cavities of the latter after starting the engine. To eliminate them, calibrated compensation holes are provided in the engine oil supply channels, providing automatic purging of the cavities of the hydraulic compensators. In addition, compensation holes allow to slightly reduce the pressure of the oil supplied to the hydraulic compensators at a high speed of rotation of the engine crankshaft, when the pressure in the cavity of the hydraulic compensator can become so great that its pusher, resting on the back of the camshaft cam, slightly opens the valve at a moment that does not correspond to the valve timing phase.
Almost all hydraulic compensator faults are diagnosed by the characteristic noise emitted by the valve timing mechanism in various engine operating modes.
Valve noise can sometimes be eliminated by slightly rotating the spring or valve around its longitudinal axis. To do this, do the following.
1. Turn the crankshaft to the position where the valve making the noise begins to open slightly.
2. Turn the spring a little - the valve will turn at the same time.
3. Start the engine. If the noise persists, repeat steps 1 and 2.
4. If turning the spring and valve does not produce the desired result, check the condition of the spring and measure the clearances between the valve stems and the valve guides (see "Disassembly, repair and assembly of the cylinder head"). Eliminate enlarged (compared to nominal) gaps.
If the valve and spring are in good condition, but the valve knocking can still be heard when the engine is running, the hydraulic compensator is faulty. Replace it as follows.
1. Remove the engine cylinder head cover (see "Replacing the cylinder head cover gasket").
2. Remove the camshafts from the cylinder head supports (see "Removal, inspection and installation of camshafts").
3. Remove the hydraulic compensator from the cylinder head socket.
Helpful Hints: It is easier to remove the hydraulic compensator using a strong magnet, as shown in the photo, or a suction cup. Before installation, place the new hydraulic compensator in a container with engine oil, press the hydraulic compensator sleeve several times to remove air from it and fill it with oil.
4. Lubricate the socket in the cylinder head with engine oil and install the hydraulic compensator into the socket.
5. The remaining hydraulic compensators are replaced in the same way.
6. Install the camshaft and timing drive components in the reverse order of removal.
