B5.9G, B5.9LPG – Troubleshooting and Repair Manual – 001-047   Piston Rings

The piston rings for naturally aspirated and turbocharged engines differ.

Check the cylinder liners for wear. For those cylinders with no obvious damage, check the following conditions that can cause loss of sealing:

1. Piston rings installed incorrectly
2. Worn or damaged piston rings.

Inspect the piston rings for the following:

• Abrasive wear.

NOTE: Abrasive wear is indicated by concentrated vertical scratches (B). The chromium plate is worn through and the face of the ring has a brighter finish compared to the dull satin finish of a new ring (A).

Abrasive wear can be caused by:

1. Ingested abrasive material
2. Inadequate cleaning during a previous repair
3. Particles embedded in the liner
4. Scuffing and scoring.

NOTE: Scuffing and scoring are indicated by heavy scratches, metal discoloration, and voids (B).

Scuffing and scoring can be caused by:

1. Engine overheating
2. Oil dilution
3. Improper maintenance of the lubrication system
4. Piston cooling nozzle malfunction
5. Oil ring plugged by deposits.

NOTE: Scuffing and scoring on the piston rings indicate a breakdown of the oil film on the cylinder liner wall, causing transfer of material from the piston ring face to the cylinder liner.

NOTE: Oil ring plugging is indicated by deposits on the oil ring grooves (B).

Oil ring plugging can be caused by:

1. Low engine operating temperatures – long periods of idling or a cooling system malfunction
2. Extended oil change intervals
3. Use of the wrong type of engine oil
4. Use of a poor-quality engine oil.

NOTE: Plugging of the oil ring drains restricts oil drainback, which floods the piston ring belt area, resulting in a loss of oil control.

Use a new piston ring to measure the clearance in the ring groove.

Position each ring in the cylinder 89 mm [3.5 in] below the top deck (A), and use a piston to square it with the bore.

Use a feeler gauge to measure the gap.

Identify the ring sets for installation in the cylinder where the end gap was measured.

CAUTION  If a ring expander tool is being used, be careful not to overexpand the ring.

The top surface of the top and intermediate rings is identified as illustrated.

The oil control ring can be assembled with either side up.

Position the oil ring expander in the control ring groove.

Install the oil control ring with the end gap 180 degrees from the ends of the expander.

Piston Ring Expander, Part Number 3823137

Install the intermediate ring.

NOTE: Make certain that the dot and the word TOP are facing up when installing the ring.

Install the top ring.

Position the rings so the ring gaps are 120 degrees apart from one another.