Valve timing mechanism — design description (BMW X5 E53)

The engine uses a valve timing mechanism with overhead intake and exhaust camshafts, the cams of which act on the valves through cylindrical hydraulic tappets.

The exhaust camshaft is driven by a roller chain from the crankshaft sprocket (Fig. 3.13), and the intake camshaft is driven by a roller chain from the exhaust sprocket, thanks to an intermediate chain.



The gas distribution mechanism (GRM) includes the cylinder head, camshafts, intake and exhaust valves, valve guide bushings, conical valve springs with fastening parts, hydraulic tappets, camshaft drive targets with tensioning and damping parts. The chain tension is adjusted by an automatic tensioner with a hydraulic damping mechanism.

The camshafts (17 and 18) of the valve drive (25, 26) have a mechanism for changing the angle of their initial position (rotation), which leads to a change in the valve opening phase - the D-VANOS system. The gas distribution mechanism (GRM) includes the cylinder head, camshafts, intake and exhaust valves, valve guide bushings, conical valve springs with fastening parts, hydraulic tappets, camshaft drive chains with tension and damping parts.



The chain tension is adjusted by an automatic tensioner with a hydraulic damping mechanism.

Camshaft

Camshafts (17, 18. Fig. 3.13) seven support, rotate in plain bearings.

The exhaust camshafts are equipped with sprockets (8. 14, 15) for the drive chains (9.16). The sprockets are connected to the camshafts via the inclined splines of the D-VANOS mechanism, which allows the position of the shafts to be changed during engine operation.

Axial displacement of the camshaft:

• nominal 0.150 mm;
• maximum permissible 0.330 mm.

Clearance between the journals of the shafts and their bearings (radial): 0.02—0.054 mm

The maximum runout in operation is 0.1 mm.

Thrust bearing width 20.0 mm.

Camshaft lobe height:

• inlet 47.7±0.06 mm;
• outlet 46.8±0.06 mm.

Valve lift:

• intake 9.7 mm;
• outlet 8.8 mm.

Maximum permissible operating diameter of camshaft journals (before renovation) — 34.86-0.02 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.