Pistons and Connecting Rods
| ITEM | DESCRIPTION |
|---|---|
| 1 | Circlip |
| 2 | Piston |
| 3 | Upper compression ring |
| 4 | Lower compression ring |
| 5 | Oil control ring |
| 6 | Separator |
| 7 | Oil control ring |
| 8 | Circlip |
| 9 | Gudgeon pin |
| 10 | Connecting rod |
| 11 | Alignment marks |
| 12 | Connecting rod cap |
| 13 | Bolts |
| 14 | Lower large end shell bearing |
| 15 | Upper large end shell bearing |
| 16 | Small end bearing |
The diameter of each piston is 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 two upper rings are marked with an 'R' which must face upwards, towards the top of the piston.
The pistons are cooled with engine oil from three piston cooling jets installed under the valley of the cylinder block.
The connecting rods are forged from high strength steel. The connecting rod cap is fracture-split from the rod to ensure precision re-assembly for shell bearing alignment. There are three grades of large end bearing available, each being color coded.
Refer to: Connecting Rod Cleaning (Engine System - General Information, General Procedures).
The correct alignment of the cap with the connecting rod is indicated by marks on adjacent faces of the two components.
The pistons are attached to the connecting rods with a gudgeon pin, which is secured with 2 circlips. The gudgeon pin is located through the small end bearing in the connecting rod which allows the piston to articulate with the linear movement of the connecting rod. The circlips locate in grooves in the piston.