11 25 671 Replacing piston rings on all pistons (N51)

WARNING: This page does not describe the selected car, but rather 16 other vehicles, including the 2013 BMW 328xi, 2013 BMW 328i, 2012 BMW 328xi, 2012 BMW 328i, and 2011 BMW 328xi. However, it is still accessible from the selected car via links, so may be relevant.

Necessary preliminary tasks:

Removing all Pistons

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.

Oil scraper ring comprises two steel band rings and a support spring.

NOTE: Oil scraper ring cannot be removed with piston ring pliers.

Put aside all piston rings in correct sequence and installation position.

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

Fig 2: Removing Plain Compression Ring And Stepped Ring Upwards With Piston Ring Pliers

Courtesy of BMW OF NORTH AMERICA, INC.

Installation:

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

Determine Gap with a feeler gauge.

Fig 3: Measuring Piston Rings End Clearance With Feeler Gauge

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NOTE: Schematic diagram of piston rings.

Installation:

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

Plain compression ring
Stepped ring "TOP"
Two-part oil scraper ring

Fig 4: Plain Compression Ring, Stepped Ring "Top" And Two-Part Oil Scraper Ring
Courtesy of BMW OF NORTH AMERICA, INC.

NOTE: Oil control 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: Piston Steel Band Rings And Support Spring

Courtesy of BMW OF NORTH AMERICA, INC.

Offset the contact points (1) of the piston rings by approx. 120° to each other but do not position above the piston pin boss.

NOTE: Illustration shows N52.

Fig 6: Contact Points Of Piston Rings

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Assemble engine.