11 25 671 Replacing Piston Rings On All Pistons (N73)

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Necessary Preliminary Tasks:

Remove pistons. Refer to 11 25 530 REMOVING AND INSTALLING/REPLACING ALL PISTONS (N73) .

Measuring axial clearance of piston rings in piston ring groove (1 and 2):

Refer to ENGINE - TECHNICAL DATA .

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

Fig 1: Measuring Piston Rings Axial Clearance

Courtesy of BMW OF NORTH AMERICA, INC.

Remove piston rings (1 and 2) with piston ring compressing pliers.

NOTE: It might not be possible to find the identification on used piston rings. Put aside piston rings in correct sequence and installation position. New pistons may only be installed together with new piston rings.

Fig 2: Removing Piston Rings With Piston Ring Compressing Pliers

Courtesy of BMW OF NORTH AMERICA, INC.

Measure end clearance.

Fig 3: Measuring Piston Ring End Clearance

Courtesy of BMW OF NORTH AMERICA, INC.

NOTE: Picture shows a schematic representation.

Installation:

Install piston rings with "TOP" to piston top.

Plain compression ring.
Stepped compression ring "Top".
Two-part oil scraper ring.
Offset the contact points of the piston rings by approx. 120° to each other but do not position above the piston pin boss.

Fig 4: Locating Piston Rings Installation Position
Courtesy of BMW OF NORTH AMERICA, INC.

Installation:

Oil control ring comprises two steel band rings (1) and a support spring (2).

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: Locating Steel Band Rings And Support Spring Of Oil Control Ring

Courtesy of BMW OF NORTH AMERICA, INC.