11 25 671 Replacing piston rings on all pistons (N52)

Necessary preliminary tasks:

Measuring axial clearance of piston rings in piston ring groove.

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

Fig 1: Measuring Axial Clearance Of Piston Rings In Piston Ring Groove

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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.

Fig 2: Identifying Compression Ring With Piston Ring Pliers

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Installation:

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

Determine Gap with a feeler gauge.

Fig 3: Checking Piston Ring Gap With Feeler Gauge

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NOTE: Schematic representation of piston rings.

Installation:

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

Plain compression ring
Stepped compression ring "Top"
Two-part oil scraper ring

Fig 4: Identifying Piston Rings Components And Position
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NOTE: Oil control ring comprises two steel band rings (1) and a support spring (2).

Installation:

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 Piston Support Spring And Steel Band Rings

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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 piston pin boss.

NOTE: See Fig 6.

Fig 6: Identifying Offset Contact Points Of Piston Rings

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Assemble engine.