Piston group — design description (BMW X5 E53)

Piston

The pistons are installed on the engine (fig. 3.12,a) from the company "Mahle" made of aluminum alloy with steel inserts.

Each piston has two compression rings and one oil scraper ring. For correct orientation of the piston when installed in the cylinder, there is an arrow on its bottom, which should face the camshaft drive, as well as a mark indicating its diameter. The piston diameter is measured at a distance of 8 mm from the lower edge of the piston skirt at an angle of 90° relative to the axis of the piston pin.

	B22	B25/B30
Piston diameter, mm
nominal	79,980	83.995
intermediate	79,993	84.009
1st repair size	80,230— 80,243	84,235— 84,259
Calculated clearance between piston and cylinder for new parts	from 0.01 to +0.04
max. allowed.	0,15
Permissible weight difference between pistons for one engine, g.	10,0

Piston pins

Piston pin (fig. 3.12, 5) steel, ground, floating type.



It is held from axial movement by two retaining rings in the piston holes for the piston pin. The pins are made in two classes, marked with color marks - black and white.

The engine piston pin diameter is 22 mm, with a manufacturing tolerance of -0.003 to -0.006 mm.

The nominal clearance between the piston pin and the piston is 0.001-0.005 mm. The clearance between the piston pin and the connecting rod upper head bushing:

• fingers with a "white" mark - 0.005-0.013 mm;
• fingers with a "black" mark - 0.008-0.015 mm.

Piston rings

The piston rings are installed in the grooves of the piston head: two compression rings (1,2) and one oil scraper ring (3).

The rings are installed on the piston with the mark "Top" ("Top") towards the bottom of the piston (fire belt). The upper compression ring is chrome-plated, with rounded edges, the lower compression ring is conical, the oil scraper ring has an expander.

Clearance between new piston ring and groove wall:

• upper compression 0.020-0.060 mm;
• lower compression 0.020-0.060 mm;
• oil scraper 0.020-0.060 mm;
• maximum permissible 0.12 mm.

Break gap of new piston ring:

• upper compression 0.10-0.30 mm;
• lower compression 0.20-0.40 mm;
• oil scraper 0.20-0.60 mm.

The maximum permissible gap in the lock for all engine models for compression rings is 0.80 mm, oil scraper rings 1.00 mm.

Connecting rods

Connecting rods (8. Fig. 3.12,b) forged, with an I-section rod made of heat-treated steel, with thin-walled trimetallic bearing liners (10, 11).

A bimetallic, collapsible part is pressed into the upper head of the connecting rod (rolled up) bushing (7).



According to the diameter of the lower head hole, the connecting rods are divided into two size groups, marked with color marks of red and blue.

Connecting rod lower head bore diameter:

• with red mark 48.000—48.008 mm;
• with blue mark 48.009—48.016 mm.

The lower connecting rod head undergoes final processing with its cover (12) and is not subject to further disassembly.

Connecting rod upper head bushing diameter:

• outer 24.060—24.100 mm;
• internal 22.011—22.005 mm;

The diameter of the lower connecting rod head, without bearing, is 48.000–48.016 mm.

The maximum permissible operating clearance between the connecting rod bearings and the crankshaft journals for all engine models is 0.12 mm. The permissible difference in weight between connecting rods on one engine is no more than 4.0 g.

The permissible twisting of the connecting rod for all engine models is no more than 30'. The tolerance of non-parallelism and skew of the axes of the holes over a length of 100 mm, for all engine models, is no more than 0.04 mm. The maximum axial clearance of the connecting rod on the crankshaft journal relative to its cheek for all engine models is no more than 0.37 mm.