Cylinder diameters
Surface roughness of cylinder mirrors, mm: 0.004. Taper and ovality of cylinder mirrors, not more than, mm: 0.01. Permissible deviation of the center of the cylinder relative to the vertical axis of the bore for the bearing: 0°5'.
BMW engine cylinder diameters «525», «528» And «528i» from model year 1978 (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 from model year 1980
Surface roughness of cylinder mirrors, µm: 3-4.
Ovality of cylinder mirrors, not more than, mm: 0.01 (except «520» with 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), no more than, mm: 0.1-0.15.
BMW «520» from model year 1978 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
Crankshaft - steel, forged, heat treated. Grinding of crankshafts subjected to heat treatment can only be carried out in the factory. The crankshafts of four-cylinder engines are five-bearing, six-cylinder engines are seven-bearing. Crankshafts are divided into two size groups, marked with red or blue marks on the main journals.
Characteristics of crankshafts
* The numerator is for crankshafts with red marks, the denominator is 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» from model year 1978, «520i» from MY 1982 66.0±0.1.
Note. From model year 1978 on models «528» And «528i» the stroke of the connecting rod journals is 80±0.1 mm. From model year 1980 on the model «5251» the stroke of the connecting rod journals is 84±0.1 mm.
Surface roughness of connecting rod and main journals, mm: 0.001-0.002
Main bearing shells
* The numerator is for crankshafts with red marks, the denominator is for crankshafts with blue marks.
Flywheel
The flywheel is attached to the crankshaft on the flange with eight bolts. Due to the presence of a centering pin, it can only be installed in one position.
Before pressing on the flywheel, the gear rim is heated to a temperature of 200-230°C (the heating temperature is controlled with a thermochromic pencil) and is mounted on the flywheel, directing the ends of the teeth from the side of the input and the engagement to the engine.
Static imbalance, no more than, g cm: 15.
Permissible runout of the flywheel when measured at a point on a diameter of 92 mm, not more than, mm: 0.03.
Permissible runout of the flywheel when measured at a point on the outer diameter, no more than, mm (BMW «520» from model year 1978, «520i» from model year 1982): 0,1.
The maximum thickness of the metal layer removed when grinding the flywheel surface under the clutch disc, mm: 0.4.
Flywheel surface thickness for clutch disc, not less than, mm:
- «518», «520»: 14,6;
- «520i», «525», «528», «528i»: 13,6;
- «520» from model year 1978, «520i» from MY 1982: 13.5.
From model year 1978 on models «525», «528» And «528i» with a manual transmission, the minimum allowable thickness of the flywheel surface for the clutch disc is 14.5 mm. Since 1980, this change has been extended to all models.
Vibration damper
From model year 1978 on BMW engines «525», «528» And «528»» a torsional vibration damper is used, having the following characteristics.
Pulley diameter along the creek, mm: 162+0.5-0.1.
Unbalance at crankshaft speed of 1000 rpm, not more than, gf cm: 8.
Radial runout when measured at a point on a diameter of 223 mm, not more than, mm: 0.2.
End runout when measured at a point on a diameter of 200 mm, not more than, mm: 0.4 (from model year 1980: 0.3-0.4).
BMW «520» from model year 1978, «5201» from model year 1982
Damper runout, no more than, mm:
- radial: 0.2;
- end: 0.3-0.4.
Connecting rods
I-section connecting rods, forged from heat-treated steel, with replaceable tri-metal liners. A cap of the lower head of a connecting rod of direct section. The bushing of the upper head of the connecting rod is collapsible, bimetallic. By mass, the connecting rods of one engine should not differ from each other by more than 4 g.
Connecting rod specifications
* From model year 1978 on BMW engines «525», «528» And «528i» The outer diameter of the bushing of the upper head of the connecting rod is 24.060-24.100 mm.
** Diametric clearance between crankpins and bearings on BMW engines «525», «528» And «528i» equal to 0.023-0.069 mm.
Connecting rod bearing shells
Connecting rod bearing shells are elastic, thin-walled, three metal.
Characteristics of connecting rod bearing shells
From model year 1978 for BMW engines «525», «528» And «528i» the following repair dimensions are entered, 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 crown is convex with a flat top.
On car models «518», «520» And «520i» pistons with modified bottoms are used after changing the shape of the combustion chambers (cm. «cylinder head»). The outer diameter of the pistons are divided into three classes (A, B, C). On the bottom of the piston, the mark of the piston group by mass is stamped («+» or «—»). On the engine, all pistons must be of the same mass group. To orient the piston when installed in the cylinder, an arrow is marked on the bottom, which should be directed towards the camshaft drive. The pistons are replaced at the same time as the pins.
Piston brand: Mahle, KS (Karl Schmidt) or A (Aican/Nural).
Piston specifications
Spare parts are supplied only with pistons of the class «IN» nominal size, intermediate size and 1st and 2nd repair sizes.
The class of piston pins is indicated by the label «W» or «S», stamped on the bottom of the piston (cm. «piston pins»).
Piston diameters are measured at a distance «A» from the piston skirt (see photo).
From model year 1978 on BMW engines «525», «528» And «528i» some piston sizes have been changed.
1. Prior to the production of standard pistons
Intermediate size, mm: class «A»: 86.040; Class «IN»: 86.050; Class «WITH»: 86,060.
Gap between piston and cylinder, mm: 0.040.
2. After the start of production of standard pistons
Marking on the bottom of the pistons: engine type / compression ratio (e.g. 2.5/9.0), skirt diameter (e.g. 89.57), as well as 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.
Gap between piston and cylinder, mm: 0.045.
Difference in mass between pistons assemblies, not more than, g: 10.
Features of BMW pistons «535i»
Piston diameter, mm:
- nominal: 93.35;
- intermediate size: 93.43;
- 1st repair size: 93.55;
- 2nd repair size: 93.75.
Gap between piston and cylinder, mm: 0.045±0.014.
Distinctive characteristics of pistons
Models «518», «520», «520i»
Models «525» And «528»
Note. Pistons class «A» are used on engines with an INAT carburetor, class «IN» - on engines with a 4A1 carburetor.
By BMW «518» class pistons «A» used with cylinder head marked «118», class pistons «WITH» - with cylinder head with label «E21 1.6».
By BMW «520» And «520i» class pistons «IN» used with cylinder head marked «E12», class pistons «WITH» - with cylinder head with label «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»
Characteristics of BMW engine pistons «520» from model year 1978 and «520i» from model year 1982
Piston diameter, mm:
- nominal: 79.98;
- intermediate size: 80.06;
- 1st repair size: 80.23;
- 2nd repair size: 80.48.
Gap between piston and cylinder, mm: 0.045±0.014.
Difference in mass of pistons in assembly, g:±10.
Piston markings: the piston diameter and an arrow are stamped on the piston head to orient the piston when installed in the cylinder.
Identification sign of pistons: height of the convex part of the piston bottom, mm: 2.1.
Piston pins
Piston pin - steel, polished. The pin rotates freely in the upper head of the connecting rod and in the piston bosses. From axial displacement, it is held by retaining rings.
Piston pin specifications
From model year 1978 on BMW engines «525» «528» And «528i» The following characteristics of the piston pins have been changed.
Diameter of the piston hole for the finger, mm:
- Mahle and KS pistons: 22+0.004.
- Alcan/Nural pistons: 22±0.003.
Gap between piston pin and piston, mm: 0.001-0.005 (for KS brand pistons and BMW engines «525» And «528»: 0,002-0,008).
Piston rings
Three rings are installed on each piston: two compression and one oil scraper. Rings are set with a label «Thor» («Up») to the bottom of the piston. The upper compression ring is cast iron, with a chrome-plated outer surface.
Piston ring specifications
* From chassis numbers 3,715,122 models «520», 3 802 199 models «520A», 3 852 364 models «520i».
** The numerator shows data for Mahle and Alcan/Nural pistons, the denominator for KS pistons