Piston Ring: Service and Repair

11 25 671 Replacing Piston Rings On All Pistons (N16)

Special tools required:







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.







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.







Determine end clearance with a feeler gauge.







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







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

1. Plain compression ring
2. Taper face ring
3. Two-piece oil scraper ring with spiral expander.

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







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

Installation note:
Insert bearing spring (2) in piston ring groove and then fit steel band ring (1) so that end faces are facing each other.







Offset the contact points (1) of the piston rings by approx. 120° to each other but do not position above the gudgeon pin boss.
Coat special tool 11 9 670 with sufficient engine oil Risk of damage to piston rings.

NOTE: See graphic.







Assemble engine.