3.5L Engine Description And Operation

Engine Description

The LX5 V6, is a 3.5 L (213.5 cu in) engine incorporating two intake and two exhaust valves per cylinder with individual cylinder head mounted camshafts for intake and exhaust functions (DOHC). The cylinder bore diameter is 89.5 mm (3.52 in) and the piston stroke is 92 mm (3.62 in). The cylinders are arranged in two banks of three with a 90 degree included angle. The left (front) bank of cylinders are number 2-4-6 and the right (rear) bank cylinders are 1-3-5. Engine firing order is 1-2-3-4-5-6. The crankshaft throws are split to provide even firing pulses 120 degrees apart.

Engine Block

The cylinder block is constructed of aluminum alloy by the die casting method and is constructed of two sections, an upper and a lower crankcase, split at the crankshaft center line. The grey cast iron cylinder liners are cast with the upper crankcase. The upper and lower crankcase sections are held in alignment by four dowel pins. Once machined, the sections must be kept together as a set. Sealing between the crankcase halves consists of a silicone rubber seal and a bead of anaerobic sealant along each side. Since the lower crankcase contains the lower main bearings, this casting adds to the structural rigidity of the engine assembly. Both upper and lower crankcases incorporate oil drain back passages isolated from the crankcase. These passages provide a direct path from the cylinder heads to the oil pan in order to prevent the needless aeration of the oil through contact with the rotating components.

Cylinder Head

The cylinder heads are semi-permanent mold cast aluminum with powdered metal valve seat inserts and valve guides. Two 31 mm (1.220 in) intake valves and two 29 mm (1.142 in) exhaust valves are actuated by roller finger followers pivoting on a stationary hydraulic lash adjuster (SHLA). Separate intake and exhaust camshafts are supported by four bearings machined into the cylinder head with camshaft thrust taken by the first bearing. The combustion chamber is roughly in the shape of a clover leaf with a nominal volume of 56.0 cc and a centrally located spark plug.

Crankshaft

The crankshaft is a cast nodular iron design with four 70 mm (2.75 in) diameter main bearings. Crankshaft thrust is taken by the number three main bearing. The position sensor, also known as the reluctor wheel, is cast integrally with the crankshaft. The crankshaft is internally balanced and incorporates a two piece modular rear seal. The connecting rod journals are 55.455 mm (2.18 in) diameter. A rolled fillet radius is incorporated on all bearing journals to improve fatigue strength.

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Piston and Connecting Rod Assemblies

The connecting rods are forged powdered metal with 59.144 mm (2.32 in) journals and have full floating piston pins. The connecting rod's crankpin end incorporates fractured joint technology which means the rod cap is "cracked" away from the once one-piece connecting rod. The cap then becomes perfectly matched at the cap to rod joint which significantly increases the strength of this joint and the rod itself. The piston pins are slip fit in the bronze bushed rods and are retained in the piston by round wire retainers. The cast aluminum pistons use two low tension compression rings and one multi-piece oil ring. The top compression ring is steel and the second compression ring is coated cast iron. The oil ring is a three piece side seal type ring which incorporates a steel expander and two chrome plated steel rails. To provide a non-scuffing surface when the engine is new, the pistons are tin plated and the top land is anodized.

Camshaft

The four overhead camshafts are driven by three separate 8 mm (0.315 in), single-row, fine pitch chains. The primary drive chain connects the crankshaft with both large intake camshaft sprockets, the balance shaft sprocket and the intermediate shaft sprocket. The exhaust camshafts are driven by short chains from the intake camshafts. Primary timing chain tension is held by a tensioner that hydraulically applies pressure to a pivoting tensioner shoe/chain guide. The hydraulic tensioner minimizes chain noise and provides accurate valve action by keeping slack out of the chain and continuously adjusting for chain wear. As the chain stretches from wear, a ratchet mechanism inside the tensioner prevents the nylon pad from retracting when the engine is turned off and engine oil pressure ceases. The intake to exhaust camshaft chain tensioner contains an internal spring that provides a constant load on the secondary timing chains.

Intake Manifold and Fuel Rail

The induction manifold is a plastic, lost core casting with a removable plastic sight shield cover. The manifold is sealed to the cylinder heads via imbedded silicone rubber around the intake ports. These gaskets are integral to the manifold and are designed to last the life of the engine.

Engine Cooling System

The coolant pump is bolted to the engine front cover and is driven by the serpentine belt via a drive pulley. The water outlet collects coolant from the cylinder head for delivery to the radiator. The water crossover also provides important functions for the EGR System. The coolant pump and its housing form an assembly which is inseparable and serviced as one unit.


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