Detailed Description B284
Detailed description B284Cylinder block
B284 is a fluid-cooled, 6-cylinder V engine made of an aluminum alloy. Then engine has a 60 degrees angle between the cylinder banks, four valves per cylinder and two overhead camshafts per bank. The engine is a cross flow type, i.e. with intake ducts on one side and exhaust ducts on the other side of the combustion chambers. The cylinder liners are steel and are cast in the cylinder block. The cylinders are completely surrounded by coolant, including between the cylinders. The four main bearing caps are mounted with six bolts each. Two of the six bolts are so-called cross bolts, constituting an important part of the stability in the bottom of the cylinder block. The thrust bearing is located at the third main bearing cap.
In order to reduce the amount of air mixed in the oil in the crankcase, return oil is led from the cylinder heads in ducts that lead to the oil sump. Thus, the return oil does not come in contact with moving parts such as the crankshaft and connecting rods.
The cylinder block also houses bored oil ducts to supply oil to bearings, the turbocharger and the cam phasing mechanism.
Cylinder head
The cylinder head is made of aluminum and has four valves per cylinder. The combustion chambers are pentroof type. Two camshafts are mounted in the cylinder head with four bearing caps. The bearing cap closest to the camshaft sprocket has cast ducts for transferring oil to the CVCP pinion of the intake camshaft.
The cylinder heads also house a position sensor for the intake camshaft and valves for CVCP control.
Crankshaft
The crankshaft is made of forged steel and has ground bearing journals, the surface of which is hardened via induction hardening. This generates a hard outer layer that protects against wear. The crankshaft is mounted in four main bearings, no. 3 of which has a thrust bearing. The crankshaft contains bored ducts for lubrication oil. The crankshaft is dynamically balanced. It is relatively compact and powerful, which reduces torsional vibration and vibration. The toothed wheel of the crankshaft position sensor is mounted on the rear edge of the crankshaft. It comprises a steel disc with 58 teeth and one space with no tooth.
Piston
The pistons are made of a light metal alloy and have grooves for two compression rings and one groove for the oil scraper ring. The piston ring grooves are hard anodized to reduce wear. The top compression ring is made of stainless steel and has a plasma coating. The other compression ring is made of cast iron and is a napier ring. Both compression rings are low tension rings. The three-piece oil scraper ring comprises two thin, chromium-plated scraper rings with an expander between. The piston ring groove is drained via four slits - two on each side of the piston. The gudgeon pin is free floating in the piston.
The piston skirts have a graphite coating in order to reduce wear and friction against the cylinder walls.
Connecting rod
The connecting rods are made of sinter-forged steel. The principle behind such is that a steel alloy in powder form is poured into a form. The form is pressed together and heated. The metal powder that is pressed together and heated to its fusing point fuses into a strong yet light connecting rod.
The greatly dimensioned small end has a bearing bushing of brass while the big end has two loose bearing shells. The top of the small end contains a bored hole for lubrication. Both bearing bushings and the bearing shells can be replaced.
The big end bearing cap is divided by splitting, which generates good fit and roundness.
Cam transmission
The engine is equipped with four overhead camshafts - two per cylinder head. A gear wheel mounted on the crankshaft drives the so-called primary chain, which is toothed. A self-adjusting hydraulic chain tensioner ensures that the primary chain has the correct tension. The chain is controlled with the help of three chain control guides.
The distribution chain drive the distribution pinion of the front and rear bank's timing chains. A timing chain runs from the distribution pinion up to the respective cylinder head. Each timing chain has two guides and a self-adjusting hydraulic tensioner.
The exhaust camshaft has a silent pinion while the intake camshaft has a hydraulic cam phasing mechanism (CVCP). The camshafts actuate rocker arms with roller bearings (aka roller finger followers) that are shaped like a ball cup at one end. This ball cup meets the ball-shaped upper part of the hydraulic valve clearance balancer. The other end of the rocker arm actuates the valve stem. The hydraulic valve clearance balancers keep the clearance between the rocker arm /roller bearing at zero. The valve clearance balancers thus do not participate in the movement of the valve mechanism.
The valves are steel with chromium-plated spindles. The exhaust valves are sodium cooled.
