Cylinder head characteristics (BMW 3 Series E21)

The cylinder head is cast from aluminum alloy. The head has three-spherical combustion chambers. The valve seats and guide bushings are pressed into the cylinder head. Cylinder head height, mm: 125.1 ±0.1.

Reduction in cylinder head height during grinding, mm. no more than: 0.3.

Thickness of the gasket in a free state, mm: 1.2.

Valve seats

Valve seats are inserted. After cooling to a temperature of minus 70°, the seats are pressed into the cylinder head, heated to a temperature of 220-250°C.

Valve seat characteristics

Valve guide bushings

The valve guides are made of cast iron and are pressed into the cylinder head.

The parameters of the inlet and outlet valve guides are the same. The valve guides are pressed into the cylinder head heated to 220-250°C.

Valve guide bushing characteristics

Valves

The valves are made of steel and are located in the cylinder head in a V-shape. The valve stems are chromed.

The clearance between the rocker arm and the valve stem is adjusted by rotating the eccentric with a lock nut located on the rocker arm.

Valve characteristics

Clearances in the valve drive mechanism

The normal clearance between the eccentric and the end of the valve stem, measured with a feeler gauge on a cold engine, is 0.25 mm for intake and exhaust valves.

Valve springs

Each intake and exhaust valve is equipped with one spring. Valve springs are installed with the color mark down, towards the cylinder head.

Valve spring characteristics

Valve drive rocker arms

The rocker arms are made of light alloy and are the same for the intake and exhaust valves. The contact points of the rocker arms with the camshaft cams are made of high-hardness cast iron. The diameter of the holes in the cylinder head for the rocker arm axles, mm: 17.5^+0,043₀.



Rocker arm hole diameter without bushing, mm: 20^+0,021₀.

Diameter of the hole in the rocker arm bushing, mm: 17.5^+0,018₀.

Rocker axle diameter: 17.5^-0,016_-0,034.

Installation clearance of rocker arm axles in cylinder head, mm: 0.016-0.077.

(Information obtained from this online resource: «BMWman»)