Td5 Technical - Block, Internals & Flywheel
The cast iron Td5 cylinder block is closely related in both construction and bore/stroke dimensions to that of the Rover L-series diesel engine, on which the Storm project was loosely based.
The engine uses ‘through-bolt’ fixings for the cylinder head, which ensures that each cylinder bores is subjected to the same compression from the head. This allows close tolerances to be used for piston rings due to the bore-to-head stablility, reducing emissions and minimising oil consumption. This is helped by diamond micro-finishing of the cylinder bores, a proven Rover method.
Other features in common with the L-series include vertical box-section channels cast into each side of the block which both stiffen the block and allowing rapid oil return.
To add further strength to the block assembly, the block is stiffened with an aluminium crankcase ladder frame with oil pump and feed galleries, and a cast aluminium sump.
As on the Tdi and L-series, each piston incorporates a re-entrant shaped combustion chamber in the centre of the top face. The carefully developed shape of the chamber provides an efficient fuel/air mixture at the beginning of combustion, and promotes complete combustion of the combustion mixture. On EU3 engines, the piston bowl is offset, and cannot be interchanged with EU2 pistons.
Two compression rings and one oil control ring are fitted to each piston, and the piston skirt is graphite coated. The upper compression ring sits in a nimonic steel insert to withstand the high combustion forces. Piston cooling is assisted by oil galleries inside the piston, fed by oil jets incorporated in the crankcase walls.
The Td5's con-rods use the modern manufacturing technique of forging the rod in one piece, and then fracture-splitting the big end cap from the main part of the rod (a practice used for many years by BMW). This technique produces a strong and accurate fixing between cap and rod.
The small end of the con-rod is tapered, to provide a large bearing area but minimum intrusion into the piston head, to optimise its strength. The con-rods are common with those of the L-series engine, and are thoroughly proven in numerous vehicle programmes as well as recording perfect reliability.
The camshaft, manufactured for Land Rover by BMW, is ground from a forged steel billet and is then case hardened. It has three cam lobes per cylinder, two to operate the valves, one to pressurised the fuel in the EUI. A duplex chain drive from the crankshaft is used for reliability, rather than a toothed belt drive, which gave problems in the 300 Tdi engine.
Following established manufacturing and design practice, the crankshaft is cast in spheroidal graphite (sg) iron, with cold-rolled fillets for high strength and excellent fatigue resistance.
The Td5 (with manual transmission) has a new design dual-mass flywheel, working in a similar manner to a crankshaft damper. The flywheel consists of two individal masses, connected by spring and damper elements. This helps smooth out individual combustion pulses from each cylinder, especially at low engine speeds. Where automatic transmission is fitted (in the Discovery), the flywheel is unnecessary since the torque converter provides this damping effect.
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