Valve timing mechanism — design description (BMW X5 E53)

The camshafts are driven by a roller chain from the crankshaft sprocket, together with the high-pressure pump (HP) drive. The valve timing mechanism includes the cylinder head with guide bushings and valve seats, camshafts, intake and exhaust valves, valve springs with fastening parts, hydraulic compensators, drive levers with roller supports under the camshaft cams, a camshaft drive chain with tensioning and damping parts. The design of the valve timing mechanism is shown in Figures 6.7 and 6.8.





The chain tension is adjusted by an automatic tensioner with a hydraulic damping mechanism. The camshaft and crankshaft sprockets are mounted on segment keys and secured with bolts.

Camshaft

The camshaft (Fig. 6.8) has seven bearings and rotates in plain bearings with a diameter of 23 mm. The drive chain sprockets are installed on the camshafts.



Thrust bearing width 19.00 – 19.10 mm.

Axial displacement of the camshaft:

• nominal - 0.150 - 0.330 mm;
• maximum permissible - 0.55 mm.

Radial clearance between the shaft journals and its bearings:

• nominal - 0.047 - 0.088 mm.
• maximum permissible - 0.1 mm.

The nominal size camshafts are marked with blue paint, the repair size - with yellow paint. The mark is applied between the first and second cams.

The timing chains are covered with protective covers, the design of the lower cover is shown in Figure 6.50, the upper part of the cover is made integral with the cylinder head cover (see fig. 6.4).