11 25 671 Replacing Piston Rings On All Pistons (N52K)

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2013 BMW 128i, 2012 BMW 128i, 2011 BMW 128i, 2010 BMW 128i, and 2009 BMW 128i. However, it is still accessible from the selected car via links, so may be relevant.

Necessary preliminary tasks:

Remove all pistons . See 11 25 530 REMOVING AND INSTALLING/REPLACING ALL PISTONS (N52K) .

Measuring axial clearance of piston rings in piston ring groove.

Technical Data.

NOTE: It is not possible to measure the axial clearance of the U-flex rings.

Fig 1: Measuring Axial Clearance Of Piston Rings In Piston Ring Groove

Courtesy of BMW OF NORTH AMERICA, INC.

Remove plain compression ring and stepped ring upwards with piston ring pliers.

The U-flex ring comprises two steel band rings and a support spring.

NOTE: The U-flex ring cannot be removed with piston ring pliers.
Put aside all piston rings in correct sequence and installation position.

Fig 2: Removing Plain Compression Ring And Stepped Ring

Courtesy of BMW OF NORTH AMERICA, INC.

It might not be possible to find the identification on used piston rings.

Installation:

New pistons may only be installed together with new piston rings.

Determine end clearance with a feeler gauge.

Fig 3: Checking Piston Rings Gap

Courtesy of BMW OF NORTH AMERICA, INC.

NOTE: Schematic diagram of piston rings.

Installation:

Piston rings with "TOP" identification must point to piston crown.

Plain compression ring
Stepped ring "TOP"
U-flex ring

Fig 4: Identifying Plain Compression Ring, Stepped Ring "Top" And U-Flex Ring
Courtesy of BMW OF NORTH AMERICA, INC.

NOTE: The U-flex ring comprises two steel band rings (1) and a support spring (2).

Installation:

Insert support spring (2) into piston ring groove and then fit steel band rings (1) so that contact points are offset by approx. 120°.

Fig 5: Identifying Steel Band Rings And Support Springs

Courtesy of BMW OF NORTH AMERICA, INC.

The contact points (1) of the piston rings must be arranged offset by approx. 120°. However, the contact points (1) must not be arranged over the piston pin boss.

NOTE: Picture shows N52.

Fig 6: Identifying Contact Points

Courtesy of BMW OF NORTH AMERICA, INC.

Assemble engine.