1125671 Replacing piston rings on all pistons (N51)

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2011 BMW 328xi, 2011 BMW 328i, 2010 BMW 328xi, 2010 BMW 328i, and 2009 BMW 328xi. However, it is still accessible from the selected car via links, so may be relevant.

Necessary preliminary tasks:

Remove all PISTONS .

Measuring axial clearance of piston rings in piston ring groove.

See 1125-N51-01B1S1 PISTONS WITH RINGS AND PINS N51/B30 .

NOTE: It is not possible to measure the axial clearance of the oil scraper rings.

Fig 1: Measuring Axial Clearance Of Piston Rings

Courtesy of BMW OF NORTH AMERICA, INC.

Remove 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 piston rings in correct sequence and installation position.

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.

Fig 2: Removing Compression Ring And Stepped Ring

Courtesy of BMW OF NORTH AMERICA, INC.

Determine gap with a feeler gauge. See 1125-N51-01B1S1 PISTONS WITH RINGS AND PINS N51/B30 .

Fig 3: Measuring Gap Using Feeler Gauge

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NOTE: Schematic representation of piston rings.

Installation:

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

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

Fig 4: Identifying Piston Rings
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: Identifying Steel Band Ring 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: See Fig 6 N52.

Fig 6: Identifying Contact Points Of Piston Rings

Courtesy of BMW OF NORTH AMERICA, INC.

Assemble engine.