Piston Ring: Service and Repair

11 25 671 Replacing piston rings on all pistons (N18)

Special tools required:





Necessary preliminary work:
^ Remove all pistons.





Measuring side 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 bearing 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 rectangular compression ring
2. Lug face ring
3. Two-part oil scraper ring





Note:
Oil scraper ring comprises two steel band rings (1) and a bearing spring (2).

Installation note:
Insert bearing spring (2) into piston ring groove and then fit steel band rings (1) so that contact points are offset by approx. 120°.





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.