Engine - Td5 (Description): Description and operation (page 3 of 7)

Pistons

1 Bowl in piston head 2 Piston ring grooves 3 Graphite coated aluminium alloy skirt 4 Gudgeon pin bore

The five pistons have graphite-compound coated aluminium alloy skirts which are gravity die cast and machined. Each of the pistons has phosphated, shaped gudgeon pin bores and a swirl chamber (bowl-in-piston) machined in the head which partly contains the inlet air that is compressed during the combustion process and helps provide turbulence for efficient air/fuel mixture to promote complete combustion. The recesses in the piston's crown also provide clearance for the valve heads.

Pre EU3 and EU3 pistons are not interchangeable due to the EU3 piston combustion bowl being offset.

The pistons are attached to the small-end of the connecting rods by fully floating gudgeon pins which are retained in the piston gudgeon pin bushings by circlips.

The pistons and gudgeon pins are gallery cooled, oil being supplied under pressure from the piston lubrication jets when the pistons are close to bottom dead centre.

Piston rings Each piston is fitted with two compression rings and an oil control ring. The top compression ring is located in a steel insert ring carrier which helps to provide a minimal reaction to compression forces.

The top ring is barrel-edged and chrome-plated, the 2nd compression ring is taper-faced and the oil control ring is chrome-plated and features a bevelled ring with spring.