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 make sure 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.
The engine uses a 3 ring piston sealing system. The steel top ring is treated with a physical vapor deposition peripheral coating. The physical vapor deposition is a coating technique where material can be deposited with improved properties to provide good cylinder bore compatibility and wear resistance. A Napier center ring helps cylinder pressure and oil management, while the lower oil control ring assembly is produced from nitrided steel. The 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 4 piston oil cooling jets installed under the valley of the cylinder block.
The connecting rods are forged from high strength steel. The connecting rod caps are fracture-split from the rods to provide precision re-assembly for shell bearing alignment. There are 3 grades of large end bearing available, each being color coded. For additional information, refer to:
and CONNECTING ROD LARGE END BORE
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.