11 25 671 Replacing piston rings on all pistons (B36A/B38A)

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Necessary preliminary tasks:

Remove all PISTONS .

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

Oil scraper ring comprises two steel band rings and a bearing spring.

NOTE: Oil scraper ring cannot be removed with piston ring pliers.

Fig 1: Removing Plain Rectangular Compression Ring And Stepped Ring

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Put aside all piston rings in correct sequence and installation position.

It might not be possible to find the identification on used piston rings.

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

Measure side clearance of piston rings in piston ring groove. Refer to technical data for PISTONS WITH RINGS AND PINS - END CLEARANCE, SIDE CLEARANCE .

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

Fig 2: Measuring Side Clearance Of Piston Rings In Piston Ring Groove

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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 technical data for PISTONS WITH RINGS AND PINS - END CLEARANCE, SIDE CLEARANCE .

Fig 3: Checking Piston Ring End Clearance With Feeler Gauge

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NOTE: The compression ring and the taper faced piston ring must be mounted with the TOP mark pointing to the piston crown (see arrow).

Piston ring (1) with TOP identification.

Taper faced piston ring (2) with TOP identification.

Oil scraper ring with spiral expander (3) without TOP identification.

Fig 4: Spiral Expander, Taper Faced Piston Ring And Piston Ring

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NOTE: Schematic diagram of piston rings.

Plain rectangular compression ring "top"
Piston ring "top"
Oil scraper rings with springs

Fig 5: Piston Rings Schematic Diagram

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Align top piston ring (K1) with the contact point at the 12 o'clock position (1).

Align middle piston ring (K2) with the contact point at the 4 o'clock position (2).

Align top oil scraper ring (O3) with the contact point at the 8 o'clock position (3).

Fig 6: Aligning Top Piston Rings And Top Oil Scraper Ring

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Align bottom oil scraper ring (O1) with the contact point at the 12 o'clock position (1).

Align spring for oil scraper ring (O2) with the contact point at the 4 o'clock position (2).

Ensure that the contact point (1) of the spring (O2) does not overlap.

Fig 7: Aligning Bottom Oil Scraper Ring And Spring

Courtesy of BMW OF NORTH AMERICA, INC.