11 25 671 Replacing piston rings on all pistons (N12)

WARNING: This page is about a different variant/trim than selected.

Special tools required:

11 9 670

Necessary preliminary tasks:

Remove 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 oil scraper rings.

Fig 1: Measuring Axial Clearance Of Piston Rings

G04207369

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.

Fig 2: Removing Piston Rings

G05515564

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: Checking Ring Gap

G04207370

Courtesy of BMW OF NORTH AMERICA, INC.

Installation:

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

Fig 4: Identifying Piston Rings With "TOP" Identification Mark

G05515566

Courtesy of BMW OF NORTH AMERICA, INC.

Installation:

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

IMPORTANT: Contact point on oil scraper ring (3) can overlap - risk of damage! - during installation in cylinder.

Fig 5: Identifying Piston Rings

G05515567

Courtesy of BMW OF NORTH AMERICA, INC.

NOTE: The oil control ring comprises a steel band ring (1) and a support spring (2).

Installation:

Insert support spring (2) in piston ring groove and then fit steel band ring (1) so that end faces point to each other.

Fig 6: Identifying Steel Band Ring And Support Spring

G04725493

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.

Coat special tool 11 9 670 with sufficient engine oil. Risk of damage to piston rings!

NOTE: See illustration.

Fig 7: Identifying Piston Head

G05515569

Courtesy of BMW OF NORTH AMERICA, INC.

Assemble engine.