BMW 3 Owners & Service Manuals

BMW 3: IROX coating - Crankshaft drive

Crankshaft drive
Detailed magnification of the IROX coating

  1. IROX-coated bearing shell
  2. Oil film
  3. IROX coating
  4. Bearing shell
  5. Binding resin
  6. Hard particle
  7. Solid lubricant

The IROX coating is applied to a conventional bearing shell. It consists of a binding resin matrix made of polyamide-imide with embedded hard particles and solid lubricants. The polyamide-imide ensures, in combination with the hard particles, that the bearing shell surface is so hard that material abrasion is no longer possible. The solid lubricants reduce surface friction and replace the oil film which briefly no longer exists between the bearing shell and the connecting rod bearing journal during the starting phase. The IROX bearings are red due to their special coating.

The IROX-coated bearing shells are only located on the connecting rod side as here the load acts mainly on the bearing shells. The bearing shell caps are equipped with a bearing shell without IROX coating.

If a connecting rod bearing cap is mounted the wrong way round or on another connecting rod, the fracture structure of both parts is destroyed and the connecting rod bearing cap is not centered. In this event the entire set of connecting rods must be replaced with new parts. In Service please observe the specified jointing torques and angle of rotation specifications in the repair instructions.

Bearing shell classification of connecting rod bearing

The connecting rod bearing shells are available in one standard size. It is therefore not necessary to follow a procedure similar to that used with the main bearing shells of the crankshaft.

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