Cylinder Block Specifications (BMW 5 Series E12)

The cylinder block is cast from a special grey cast iron and is one piece with the cylinders. Grinding the plane of the cylinder block joint with the head is not permitted.

Cylinder diameters

Roughness of cylinder mirror surfaces, mm: 0.004. Taper and ovality of cylinder mirrors, no more than, mm: 0.01. Permissible deviation of the cylinder center relative to the vertical axis of the bearing bore: 0°5'.

BMW Engine Cylinder Diameters "525", "528" and "528i" from the 1978 model year (for standard pistons), mm:

• nominal: 86.015±0.005;
• intermediate size: 86.095±0.005;
• 1st repair size: 86.265±0.005;
• 2nd repair size: 86.515±0.005.

Cylinder diameters since 1980 model year

Roughness of cylinder mirror surfaces, µm: 3-4.



Ovality of cylinder mirrors, no more than, mm: 0.01 (except for "520" with a 6-cylinder engine: 0.01-0.02).

Taper of cylinder mirrors, not more than, mm: 0.02.

Permissible clearance between piston and cylinder (when worn out), no more than, mm: 0.1-0.15.

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

Nominal cylinder diameter, mm: 80.00±0.01.

Intermediate diameter, mm: 80.08±0.01.

1st repair size, mm: 80.25±0.01.

2nd repair size, mm: 80.50±0.01.

Permissible taper and ovality of the cylinder mirror, mm: 0.02.

Maximum clearance between piston and cylinder, mm: 0.10-0.15.

Crankshaft

The crankshaft is steel, forged, and heat-treated. Grinding of heat-treated crankshafts may only be carried out in factory conditions. Crankshafts of four-cylinder engines have five bearings, while crankshafts of six-cylinder engines have seven bearings. Crankshafts are divided into two size groups, marked with red or blue marks on the main journals.

Characteristics of crankshafts

* The numerator shows the values for crankshafts with red marks, the denominator shows the values for crankshafts with blue marks.

Stroke of connecting rod journals, mm:

• "518": 71,0±0,1;
• "520", "520i": 80,0±0,1;
• "525", "528", "528i": 71,6±0,1;
• "520" since 1978 model year, "520i" since 1982 model year 66.0±0.1.

Note: Since MY 1978, the crankpin stroke on the 528 and 528i models is 80±0.1 mm. Since MY 1980, the crankpin stroke on the 5251 model is 84±0.1 mm.

Surface roughness of connecting rod and main journals, mm: 0.001-0.002

Main bearing shells

* The numerator shows the values for crankshafts with red marks, the denominator shows the values for crankshafts with blue marks.

Flywheel

The flywheel is mounted on the crankshaft on a flange with eight bolts. Due to the presence of a centering pin, it can only be installed in one position.

Before pressing onto the flywheel, the toothed rim is heated to a temperature of 200-230°C (the heating temperature is controlled using a thermochromic pencil) and is installed on the flywheel, directing the ends of the teeth from the input side and the engagement towards the engine.

Static imbalance, no more than, g cm: 15.

Permissible flywheel runout when measured at a point on a diameter of 92 mm, no more than, mm: 0.03.

Permissible flywheel runout when measured at a point on the outside diameter, no more than, mm (BMW "520" from the 1978 model year, "520i" from the 1982 model year): 0.1.



Maximum thickness of the metal layer removed when grinding the flywheel surface under the driven clutch disc, mm: 0.4.

Thickness of flywheel surface under clutch driven disk, not less than, mm:

• "518", "520": 14,6;
• "520i", "525", "528", "528i": 13,6;
• "520" since 1978 model year, "520i" since 1982 model year: 13.5.

Since the 1978 model year on models "525", "528" and "528i" with manual transmission, the minimum permissible flywheel surface thickness under the driven clutch disc is 14.5 mm. Since 1980, this change has been extended to all models.

Torsional vibration damper

Since model year 1978 on BMW engines "525", "528" and "528" uses a torsional vibration damper with the following characteristics.

Pulley diameter along the stream, mm: 162^+0,5_-0,1.

Imbalance at crankshaft speed of 1000 rpm, no more than, gf cm: 8.

Radial runout when measured at a point on a diameter of 223 mm, no more than, mm: 0.2.

End runout when measured at a point on a diameter of 200 mm, no more than, mm: 0.4 (since 1980 model year: 0.3-0.4).

BMW "520" since 1978 model year, "5201" since 1982 model year

Damper runout, no more than, mm:

• radial: 0.2;
• end: 0.3-0.4.

Connecting rods

Connecting rods of I-section, forged from heat-treated steel, with replaceable trimetallic liners. The lower connecting rod head cover is of straight section. The upper connecting rod head bushing is rolled, bimetallic. The connecting rods of one engine must not differ from each other by more than 4 g in weight.

Connecting rod characteristics

* Since model year 1978 on BMW engines "525", "528" and "528i" the outer diameter of the connecting rod upper head bushing is 24.060-24.100 mm.



** Diametrical clearance between crankpins and bearings on BMW engines "525", "528" and "528i" is 0.023-0.069 mm.

Connecting rod bearing shells

The connecting rod bearing liners are elastic, thin-walled, and made of three metals.

Characteristics of connecting rod bearing liners

From model year 1978 for BMW engines "525", "528" and "528i" the following repair dimensions have been introduced, mm:

• 1st: 2.108-2.118;
• 2nd: 2.233-2.243;
• 3rd: 2.358-2.368.

Pistons

The pistons are cast from aluminum alloy, the piston bottom is convex with a flat top.

On cars of models "518", "520" and "520i" use pistons with modified bottom shapes following the change in the shape of the combustion chambers (see "Cylinder head"). According to the outer diameter, the pistons are divided into three classes (A, B, C). The piston group mark by weight ("+" or "-") is stamped on the piston bottom. All pistons on the engine must be of the same weight group. To orient the piston when installing it in the cylinder, an arrow is applied to the bottom, which must face the camshaft drive. The pistons are replaced simultaneously with the pins.



Piston brand: Mahle, KS. (Karl Schmidt) or A (Aican/Nural).

Piston characteristics

Only pistons of class "B" of nominal size, intermediate size and 1st and 2nd repair sizes are supplied as spare parts.

The class of piston pins is indicated by the mark "W" or "S" stamped on the piston crown (see "Piston pins").

The piston diameters are measured at a distance "A" from the piston skirt (see photo).



Since model year 1978 on BMW engines "525", "528" and "528i" some piston dimensions have been changed.

1. Before the start of production of standard pistons

Intermediate size, mm: class "A": 86.040; class "B": 86,050; class "C": 86,060.

Clearance between piston and cylinder, mm: 0.040.

2. After the start of production of standard pistons

Marking on the piston bottom: engine type/compression ratio (for example, 2.5/9.0), piston skirt diameter (for example, 89.57), and also an arrow for orienting the piston in the cylinder during installation. Piston diameter, mm:

• nominal: 85,970;
• intermediate size: 86,050;
• 1st repair size increased by 0.25 mm: 86.220;
• 2nd repair size increased by 0.50 mm: 86.470.

Clearance between piston and cylinder, mm: 0.045.

The difference in weight between the pistons in the assembly, no more than, g: 10.

BMW "535i" piston specifications

Piston diameter, mm:

• nominal: 93.35;
• intermediate size: 93.43;
• 1st repair size: 93.55;
• 2nd repair size: 93.75.

Clearance between piston and cylinder, mm: 0.045±0.014.

Distinctive characteristics of pistons

Models "518", "520", "520i"

Models "525" and "528"

Note: Class "A" pistons are used on engines with INAT carburetors, class "B" pistons are used on engines with 4A1 carburetors.

On the BMW "518" class "A" pistons are used with a cylinder head marked "118", class "C" pistons are used with a cylinder head marked "E21 1.6".

On the BMW "520" and "520i" class "B" pistons are used with a cylinder head marked "E12", class "C" pistons - with a cylinder head marked "E21 2.0".

Distance "A" (see photo) from the skirt, on which the outer diameter of the piston is measured

Models "518" and "520"

Models "525" and "528"

Piston characteristics of BMW engines "520" from 1978 model year and "520i" from 1982 model year

Piston diameter, mm:

• nominal: 79.98;
• intermediate size: 80.06;
• 1st repair size: 80.23;
• 2nd repair size: 80.48.

Clearance between piston and cylinder, mm: 0.045±0.014.

Difference in mass of assembled pistons, g: ±10.

Piston markings: the piston diameter and an arrow for guiding the piston when installing it in the cylinder are stamped on the piston bottom.

Identification feature of pistons: height of the convex part of the piston bottom, mm: 2.1.

Piston pins

The piston pin is steel and ground. The pin rotates freely in the upper head of the connecting rod and in the piston bosses. It is held from axial displacement by retaining rings.

Piston pin characteristics

Since model year 1978 on BMW engines "525" "528" and "528i" the following piston pin specifications have been changed.

Piston hole diameter for pin, mm:

• pistons of Mahle and KS brands: 22+0.004.
• alcan/Nural pistons: 22±0.003.

Clearance between piston pin and piston, mm: 0.001-0.005 (for KS pistons and BMW "525" and "528" engines: 0.002-0.008).

Piston rings

Each piston has three rings: two compression rings and one oil scraper ring. The rings are installed with the "Top" ("Up") mark toward the piston bottom. The upper compression ring is cast iron, with a chromed outer surface.

Characteristics of piston rings

* Starting with chassis numbers 3 715 122 for the "520" model, 3 802 199 for the "520A" model, 3 852 364 for the "520i" model.

** The numerator shows the data for Mahle and Alcan/Nural pistons, the denominator shows the data for KS pistons.