11 25 671 Replacing piston rings on all pistons (N54, N54T)

Necessary preliminary tasks

Measuring axial clearance of piston rings in piston ring groove. See

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

Fig 1: Measuring Piston Rings Axial Clearance

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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 note:

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

Fig 2: Removing Compression Ring And Stepped Ring Using Piston Ring Pliers

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Fig 3: Measuring Piston Ring Gap

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NOTE: Schematic diagram of piston rings.

Installation note:

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

Plain compression ring
Piston ring "top"
Two-part oil scraper ring

Fig 4: Identifying Piston Rings (Plain Compression, Stepped Compression And Oil Scraper)
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NOTE: Oil control ring comprises two steel band rings (1) and a support spring (2).

Installation note:

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 Rings And Support Spring

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Offset the contact points (1) of the piston rings by approx. 120° to each other but do not position above the gudgeon pin boss.

NOTE: See Fig 6 N52.

Fig 6: Identifying Piston Rings Contact Points Angle

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Assemble engine.