BMW S58 Owner's Handbook Manual page 32

S58￿Engine
4.￿Engine￿Mechanical
4.2.3.￿Piston￿with￿wrist￿pin￿and￿piston￿rings
The￿shape￿and￿material￿properties￿of￿the￿piston￿have￿been￿adapted￿to￿the￿higher￿demands￿in￿terms￿of
the￿high-revving￿design￿of￿the￿S58￿engine￿with￿a￿rated￿engine￿speed￿of￿7500 rpm.
A￿forged￿slipper-skirt￿piston￿made￿by￿the￿manufacturer￿Mahle￿is￿used.￿The￿piston￿is￿made￿from￿the
M142P￿alloy￿(AlSi12Cu3Ni2Mg).￿This￿alloy￿is￿particularly￿suitable￿for￿high-performance￿petrol￿engines.
For￿the￿S58￿engine,￿the￿piston￿alloy￿is￿formed￿by￿forging,￿which￿produces￿slightly￿different￿micro-
structures￿and￿properties.￿That￿is￿indicated￿by￿the￿suffix￿"P"￿in￿the￿alloy￿designation.
The￿piston￿skirt￿is￿Grafal-coated,￿which￿is￿necessary￿due￿to￿the￿LDS-coated￿cylinder￿liners.
The￿piston￿diameter￿is￿84 mm.￿The￿first￿piston￿ring￿is￿a￿nitride￿plain￿rectangular￿compression￿ring.
The￿2nd￿piston￿ring￿is￿a￿taper-faced￿piston￿ring.￿The￿oil￿scraper￿ring￿is￿a￿nitride￿ES￿oil￿scraper￿ring.
S58￿engine,￿piston￿with￿wrist￿pin￿and￿piston￿rings
Index

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2
3
26
Explanation
Plain￿compression￿ring
Taper-faced￿piston￿ring
ES￿oil￿scraper￿ring