Pistons And Connecting Rods
The diameter of each piston is graded and precisely matched to each cylinder bore to help reduce noise. In the vertical plane, the pistons have a slight barrel form, which helps to ensure a reliable oil film is maintained between the piston and the cylinder bore. A solid film lubricant coating is applied to both reaction faces of the piston to reduce wear and improve fuel economy.
A three-ring piston-sealing system is used. The steel top ring is treated with a PVD (physical vapor deposition) peripheral coating. PVD is a coating technique where material can be deposited with improved properties to ensure good cylinder bore compatibility and wear resistance. A Napier center ring helps cylinder pressure and oil management, while the three-piece oil control lower ring is produced from nitrided steel.
The connecting rods are forged from high strength steel. The cap is fracture-split from the rod to ensure precision re-assembly for bearing shell alignment. There are three grades of large end bearing available, each being color coded.
Cap Alignment with Connecting Rod
| Item Number | Description |
|---|---|
| 1 | Alignment marks |
| 2 | Connecting rod |
| 3 | Cap |
| 4 | Bearings |
The correct alignment of the cap with the connecting rod is indicated by marks on adjacent faces of the two components.
Connecting Rod and Piston Orientation
| Item Number | Description |
|---|---|
| A | Front of engine |
| 1 | Alignment mark |
| 2 | LH side (bank B) |
| 3 | Alignment mark |
| 4 | RH side (bank A) |
| 5 | Piston orientation arrow |
The orientation of the connecting rods and pistons on the crankshaft are given below:
- Bank A - The arrow on the piston crown must face the front of the engine and the cap and connecting rod alignment marks must face the rear of the engine.
- Bank B - The arrow on the piston crown must face the front of the engine and the cap and connecting rod alignment marks must face the front of the engine.