Piston Ring: Service and Repair

11 25 671 - Replacing piston rings on all pistons (N12)





Special tools required:
- 11 9 670 11 9 670 Bush





Necessary preliminary tasks:
- Remove all pistons Service and Repair.





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





Determine gap with a feeler gauge.





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





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

1. - Plain compression ring
2. - Taper face ring
3. - Two-part oil scraper ring

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:
Insert support spring (2) in piston ring groove and then fit steel band ring (1) so that end faces point to each other.





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

Note:
See illustration.





Assemble engine.