Valves and springs — design description (BMW X5 E53)

The valves are made of special, corrosion-resistant steel, chrome-plated, and are hardened rods, which are located in the cylinder head in a V-shape, at an angle of 30.5°. They are driven by the cams of the intake and exhaust overhead camshafts through hydraulic tappets. The drive system is implemented according to the DOHC scheme. The parameters of the valves of the "N62B44" engine are given in Table 5.4.

Table 5.4. Engine valve parameters

Valve parameters	Valve
	inlet	outlet
Engine model "N62B44"
Valve seat bearing surface	34,5	28,6
Head plate diameter, mm	35,0	29,0
- manufacturing tolerance	+0,10
Rod diameter, mm
- nominal	6,00
- approval of use. vp.	from -0.025 to -0.040
– approval of the used version.	from -0.033 to -0.047
Clearance between valve guides and valve stems, mm*	0,5

* The measurement technique is shown in Figure 3.7.



The minimum height of the cylindrical part of the valve plate "b" (Fig. 5.6) is 0.5 mm.



The condition of the valve mechanism is judged by one of the main indicators of engine wear - the compression value in its cylinders, which is checked by a special device - a compression gauge installed in the spark plug hole. The rules for its installation and taking measurements are given in the instructions for the device and described below.



The reading of the device for a new engine is 12–14 bar (kgf/cm²), with minimal valve lift. At maximum wear, this value should be no less than 10.0 bar. The difference in pressure between the cylinders of one engine should not exceed 1.5 bar. If the difference is more than 1.5 bar or the pressure is less than 10.0 bar, this indicates increased wear of the piston rings, cylinder mirrors, and valves. Such an engine is subject to removal and repair.

Valve springs

Valve springs are designed to ensure a tight fit of the valves on the seats. Each intake and exhaust valve has one spring of a complex cylindrical-conical shape. The springs are not identical for intake and exhaust valves, do not confuse them.