11 25 671 Replacing piston rings on all pistons (B48B)

WARNING: This page is about a different car, the 2018 BMW 330i and 2017 BMW 330i. However, it is still accessible from the selected car via links, so may be relevant.

Necessary preliminary tasks:

Remove all PISTONS .

Measuring side clearance of piston rings in piston ring groove:

Refer to PISTONS AND PISTON RINGS - TECHNICAL DATA .

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

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

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

NOTE: The M-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.

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

Insert removed piston ring into cylinder bore hole.

With aid of piston (piston crown), position piston ring in its measuring position.

Determine end clearance with a feeler gauge. Refer to PISTONS AND PISTON RINGS - TECHNICAL DATA .

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NOTE: Schematic diagram of piston rings.

Plain rectangular compression ring "top"
Piston ring "top"
Steel band with M-flex ring

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NOTE: Piston rings with "TOP" identification (1) must point to piston crown.

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NOTE: The M-flex ring comprises two steel band rings (1) and a bearing spring (2).
Insert bearing spring (2) into piston ring groove and then fit steel band rings (1) so that contact points are offset by approx. 120°.

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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.

G12700983

Courtesy of BMW OF NORTH AMERICA, INC.

Required follow-up work:

Install all PISTONS
Assemble engine