Cylinder Head Specifications (BMW 5 Series E12)

The head is cast from an aluminum alloy and contains combustion chambers with transverse gas movement (models "518", "520", "520i") or three-spherical combustion chambers (models "525", "528"). The valve seats and guide bushings are pressed into the cylinder head.

On the "518" model, starting with chassis No.4 625 659, on the "520" model, starting with chassis No.4 712 954, on the "520i" model, starting with chassis No.4 453 077, the design of the combustion chambers was changed in order to unify them with the "525" and "528" models.

Cylinder head height, mm: 129±0.1.

Reduction in cylinder head height during grinding, no more than, mm: 0.5 (in this case it is necessary to grind the distributor cover to the same extent).

Since the 1980 model year, the following minimum cylinder head height after grinding has been established, mm: "518": 128.6; "525": 128,6; "528i": 128,6; "535i": 128,6.

Permissible height of the cylinder head after grinding ("520" from 1978 model year, "520i"), not less than, mm: 124.7.

Cylinder head gasket

The cylinder head gasket is installed in one position only, dry, except for the front part (from the camshaft drive side), on which apply a sealant such as "Atmosit" or "Kuril K2".

The "520i" model has reinforced metal cylinder head gasket linings. This type of gasket can also be used for the carburettor engine of the "520" model. It is not allowed to install the cylinder head gasket of the carburettor engine of the "520" model on the "5201" engine with fuel injection. Gasket thickness (not compressed), mm: 1.2.

Valve seats

Valve seats are insert type.

Valve seat characteristics of the engine model "518"

Characteristics of valve seats of engines of models "520", "520i", "525", "528"

* "525": 1.60-2.00 mm.
** "525": 2.00-2.40 mm.

Since model year 1978 on BMW models "525", "528" and "528i" the following valve seat characteristics have been changed.

Working chamfer width, mm:

• intake valves: 1.6-2.0;
• exhaust valves: 2.0-2.4.

Chamfer angle of inlet and outlet valves: 45°30'+20'.

New valve seat sizes were introduced for the 1980 model year

Since the 1982 model year, the BMW "518i" has an outside diameter of the inlet valve seats and a diameter of the seat seats of 47.35 and 47.35 H7 mm, respectively. During repairs, the dimensions are increased by 0.20 mm. BMW "520" since the 1978 model year and "520i".



Outer diameter of seats, mm: inlet valves: 42.35; exhaust valves: 37.85.

Repair size of seats, mm: +0.20.

Seat seat diameter, mm: intake valves: 42.35 H7; exhaust valves: 37.85 H7.

Bevel angle: 45°.

Working chamfer width, mm: inlet valves: 1.6-2.0; graduation: 2.0-2.4.

Valve guide bushings

The valve guides are made of special cast iron and are pressed into the cylinder head. The dimensions of the inlet and outlet valve guides are the same.

Valve guide specifications for all models

Since 1978 modal year on models "525", "528" and "528i" interference fit when pressing valve guide bushings into the cylinder head, mm: 0.015-0.044.

Since the 1980 modal year the following characteristics have changed.

Length (for aces models), mm: 50.5.

Outside diameter of guide bushings/diameter of seat in cylinder head (for all models) mm: 14/14 H7.

Inner diameter (for all models), mm: 8 H7.

Protrusion of guide bushings relative to cylinder head plane, mm: "518": 15; "525", "528i" and "5351": 13.5.

Valve guide specifications for the 1970 model year 520 and 520i.

Length, mm: 45.

Inner diameter, mm: 4 H7.

Protrusion of bushings relative to the plane of the cylinder head, mm: 14.5.



Outer diameter of bushing/diameter of socket in cylinder head, mm: 13/13 H7.

Repair dimensions: 1st: increased by 0.1 mm; 2nd: increased by 0.2 mm; 3rd: increased by 0.3 mm.

Heating temperature of the cylinder head when pressing in guide bushings, °C: 220-250.

Valves

The valves are made of special steel, the stems are chromed. In the cylinder head, the valves are arranged in a V-shape and are actuated by an overhead camshaft.

Valve characteristics

* The values in brackets are for BMW "525" and "528".

Clearances in the valve drive mechanism

The normal clearance between the rocker arm eccentric and the end of the valve stem, measured with a feeler gauge on a cold engine, is for the intake and exhaust valves "518", "520", "520i" 8.15-6.20 mm, on "525", "528" - 0.25-0.30 mm.

From model year 1978 onwards "525", "528" and "528i" some valve characteristics have been changed.

Total length of valves, mm:

• intake: 106.5±0.2;
• graduation: 107.5±0.2.

Nominal height from plate to valve head chamfer, mm:

• inlet: 1.5±0.15;
• graduation: 2.2±0.1.

Minimum height of valve head edge, mm:

• intake: 1.2;
• graduation: 1.9.

Maximum permissible warping between the working chamfer and the stem of the inlet and outlet valves, no more than, mm: 0.02.



Nominal clearance between valve guides and valve stems, mm:

• intake: 0.025-0.055;
• graduation: 0.040-0.070.

Maximum allowable gap (when worn out), mm: 0.15.

The following specifications were changed for all models starting with the 1980 model year.

Minimum valve head height, mm:

• intake: 1.3;
• graduation: 2.0.

Maximum allowable clearance between valve guides and valve stems (when worn out), mm: 0.15.

BMW "520" from 1978 model year and "520i"

Minimum height of valve head edge after grinding, mm:

• intake valves: 1.3;
• exhaust valves: 2.0.

Maximum allowable clearance between valve guides and valve stems (when worn out), mm: 0.15.

Clearances in the valve drive mechanism

The normal clearance between the rocker arm eccentric and the end of the valve stem, measured with a feeler gauge on a cold engine (oil temperature 35°C), is 0.25 mm for intake and exhaust valves.

Valve springs

Valve springs are the same for both intake and exhaust valves. The springs are installed with the color mark facing down and toward the cylinder head.

Valve spring characteristics

From model year 1978 onwards "525", "528" and "528i" the length of the springs is 37.6 mm under a load of 28.45 kgf and 28.5 mm under a load of 68.67 kgf.

Valve drive rocker arms

The rocker arms are made of light alloy, the points of contact between the rocker arms and the camshaft cams are made of high-hardness cast iron.

Rocker arm hole diameter, mm: 15.5⁺⁰_-0,018.

Rocker shaft diameter, mm: 15.5^-0,016_-0,034.

Clearance between rocker arms and axle, mm: 0.016-0.077.

From model year 1978 onwards "525", "528" and "528i" the rocker arm hole diameter is 15.5^+0,043, the gap between the rocker arms and the axle is 0.016-0.052 mm.

The latest change applies to all models from the 1980 model year onwards.

BMW "520" from 1978 model year and "520i"

Clearance between rocker arms and axle, mm: 0.010-0.052.