11 25 671 Replacing piston rings on all pistons (N52T)

Necessary preliminary work:

Removing all PISTONS

Measuring axial clearance of piston rings in piston ring groove. See PISTONS WITH RINGS AND PINS (N52T) .

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

Fig 1: Measuring Piston Rings Side Clearance

Courtesy of BMW OF NORTH AMERICA, INC.

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

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

NOTE: The U-flex 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 Rectangular Compression Ring And Stepped Ring

Courtesy of BMW OF NORTH AMERICA, INC.

Installation note:

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

Determine end clearance with a feeler gauge. See PISTONS WITH RINGS AND PINS (N52T) .

Fig 3: Checking Piston Ring End Clearance Using Feeler Gauge

Courtesy of BMW OF NORTH AMERICA, INC.

NOTE: Schematic diagram of piston rings.

Installation note:

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

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

Fig 4: Identifying Piston Rings
Courtesy of BMW OF NORTH AMERICA, INC.

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

Installation note:

Insert bearing 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 Spring

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 gudgeon pin boss.

NOTE: Picture shows N52.

Fig 6: Identifying Piston Contact Points

Courtesy of BMW OF NORTH AMERICA, INC.

Assemble engine.