Cylinder head — design description (BMW X5 E53)

The design of the cylinder head is shown in Fig. 4.5 and Fig. 4.6.





The cylinder head (Fig. 4.5) is cast from an aluminum alloy. It contains two camshafts on plain bearings, intake and exhaust valves with their closing springs. The valves move in pressed-in guides. The valve seats are pressed into the cylinder head. The valve camber angle is 39.5°. The valves are driven by camshaft cams through cylindrical hydraulic tappets (hydraulic tappets), valve clearances are compensated automatically and their adjustment is eliminated. The cylinder head has oil channels to supply hydraulic tappets and other elements with oil.

Allowable warpage (non-flatness) the mating surface of the head with the cylinder block for all engines is no more than 0.03 mm.



The nominal/minimum height of the cylinder head of the M62 series engines is 140.0/139.70 mm, respectively.

Cylinder head gasket

Pad (1, Fig. 4.6) the cylinder head is made of synthetic materials (asbestos-free) with metal edging of the holes for the cylinders.

The gasket is installed with the "Oben" ("Top") mark toward the cylinder head. The thickness of the new gasket is 1.2 mm.

After grinding the cylinder head, install a repair size gasket on the engine, 1.5 mm thick (+0.3 mm).

Valve seats

Valve seats (see fig. 3.5) they are made of austenitic steel obtained by powder metallurgy and are not replaceable.



If traces of burning or wear are detected that cannot be removed by grinding, the cylinder head is replaced entirely. In this case, it is necessary to maintain the maximum permissible size. If this size is exceeded, the reliability of the gap compensation during operation of the hydraulic tappets is impaired. The valve seat is ground in (under repair) until a reliable valve spot is obtained. Valve seats have an additional narrowing - the angle of external correction, and during processing it is necessary to maintain it - 15°.



The technology for grinding valve seats is identical for all gasoline engines.

Valve seat characteristics

Parameters	Valve seat
	intake	graduation
Valve seat diameter, mm
- nominal	34,5	30,0
- admission	from 0.00 to 0.025
Working chamfer angle, deg	45	45
Correction angle, external	15	15
Correction angle, internal	60	60
Working chamfer width (B44), mm	1,25±0,25	1,65±0,35
Working chamfer width (B46), mm	0,95±0,30	1,50±0,35

Valve guide bushings

The valve guide bushings are made of a special brass alloy based on bronze and are pressed into the cylinder head. The parameters of the inlet and outlet valve guide bushings are the same. Check the clearance using the device (see fig. 3.7).



Maximum allowable gap (during operation), between the valve stem and the guide bushing is measured by the maximum displacement of the valve head when the valve stem is flush with the upper edge of the guide. In this case:

Inner diameter, mm:

• nominal - 6.00
• 1st repair size - 6.10
• 2nd repair size - 6.20

Execution tolerance – from 0.00 to + 0.015
Maximum clearance rod/bushing – 0.50

Valves

The valves are hardened rods made of special corrosion-resistant steel with chromium plating and are located in the cylinder head in a V-shape, at an angle of 39.5°. They are driven by the cams of the intake and exhaust overhead camshafts through hydraulic tappets. The drive system is made according to the DOHC scheme. The parameters of the engine valves are given in the table.



Minimum height of the cylindrical part of the valve disc "b" (see fig. 5.6) – 0.5 mm.

One of the main indicators of engine wear depends on the condition of the valve mechanism – the amount of compression in its cylinders, which is checked with a special device – a compression meter (see fig. 3.31), installed in the spark plug hole.



The rules for its installation and taking measurements are given in the device manual and described below. The device reading for a new engine is 12–14 bar (kgf/cm²), 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.

Engine valve parameters

Valve parameters	Engine model
	M62B44	M62B46
Intake valves
Plate diameter, mm	35,00	35,00
Tolerance for head diameter, mm	from 0.00 to -0.016
Rod diameter, mm
- nominal	6,00
- 1st repair	6,10
- 2nd repair	6,20
- execution tolerance	from -0.025 to -0.040
Clearance between valve guides and valve stems, mm*	0,5
Exhaust valves
Head diameter, mm	30,50	30,50
Tolerance for head diameter, mm	from 0.00 to -0.016
Rod diameter, mm
- nominal	6,00
- 1st repair	6,10
- 2nd repair	6,20
- execution tolerance	from -0.045 to -0.055
Clearance between valve guides and valve stems, mm*	0,5

* The measurement technique is shown in Fig. 3.7.

Valve springs

Valve springs (see fig. 4.12) are designed to ensure a tight fit of the valves on the seats.



Each intake and exhaust valve has one spring of a complex shape - cylindrical-conical. The springs are identical for both intake and exhaust valves.

Hydraulic tappets

Hydraulic tappets are installed directly in the cylinder head body. The valves are driven by the camshaft cams through the plungers of the hydraulic tappets. Clearances in the valve drive mechanism are compensated automatically by hydraulic tappets. The design and operating principle of these hydraulic tappets are similar to the M54 engine (see fig. 3.9).





Free travel of piston pushers is no more than 0.1 mm.