1999 GM 6.5L V8 – Engine Component Description

Cylinder Block
The engine block is made of cast iron and it has eight cylinders arranged in a V shape, with four cylinders in each bank. The engine block is a one piece casting with the cylinders encircled by coolant jackets.

Cylinder Head
The cylinder heads are made of cast iron. They have parent metal intake and exhaust valve guides, and parent metal intake and exhaust valve seats. The intake and exhaust valve seats are induction hardened for durability. Pre-combustion chambers manufactured from NIMONIC-80 (a high strength, heat resistant alloy) are located with each set of intake/exhaust valves. Glow plugs are located between each set of intake/exhaust valves, in the side of the cylinder head, protruding in to the pre-combustion chamber.

A steel camshaft is supported by five bearings pressed into the engine block. The camshaft sprocket is mounted to the front of the camshaft and is driven by the crankshaft sprocket through a timing chain. Motion from the camshaft is transmitted to the valves by hydraulic roller-type hydraulic valve lifters, valve pushrods, shaft-mounted rocker arms. The valve guides are integral to the cylinder head. A spiral drive gear machined into the camshaft near the rear journal operates the oil pump drive assembly.

The crankshaft is made of cast nodular iron, with fillet ground main bearing journals. The crankshaft is supported by five precision fit crankshaft bearings, retained by the crankshaft bearing caps. The crankshaft bearing caps are machined with the engine block for proper alignment and clearance. The crankshaft bearing caps are retained by four bolts each. The number three crankshaft bearing at the center of the engine block is the thrust bearing.
The four connecting rod journals (two rods per journal) are spaced 90 degrees apart. The crankshaft position sensor reluctor ring has four lugs used for crankshaft timing, and is integral to the crankshaft sprocket.

Pistons and Connecting Rods
The pistons are cast aluminum alloy that use two compression rings and one oil control ring assembly. The piston pins are full floating in the pistons and in the connecting rods, with spring steel retainers at each end of the piston pin bore. The connecting rods are forged steel and have precision insert type crankpin bearings.

Valve Train
The valve train is a shaft-mounted rocker arm type.
Motion is transmitted from the camshaft through hydraulic roller-type valve lifters, and tubular valve pushrods, to the valve rocker arms. The valve rocker arm pivots on a shaft in order to open the valve.
The hydraulic roller-type valve lifters keep all parts of the valve train in constant contact. Each valve lifter act as an automatic adjuster and maintains zero lash in the valve train. This eliminates the need for periodic valve adjustment. The valve rocker arms are located and retained by nylon retainers press fit to the valve rocker arm shaft, and by the valve rocker arm shaft retaining bolts. The valve rocker arm shaft retaining bolts are installed into the cylinder head.

Intake Manifold
The intake manifold is a two-piece design. Both the upper and lower portions are made of cast aluminum.
A linear exhaust gas recirculation (EGR) port is cast into the upper and lower intake manifold for exhaust gas recirculation mixture (L56 only). The EGR valve bolts into the upper intake manifold (L56 only). A Manifold Absolute Pressure (MAP) sensor is mounted at the front of the upper intake manifold and sealed by an O-ring seal.

Exhaust Manifold
The two exhaust manifolds are constructed of cast iron. The exhaust manifolds direct exhaust gases from the combustion chambers to the turbocharger.

The turbocharger is used to increase the amount of air that enters the engine’s cylinders. The increase of air allows a proportional increase of fuel that is injected into the cylinders. The results are:
• Increased power output.
• More complete combustion of the fuel.
• Cooling of the cylinder heads, the pistons, the valves, and the exhaust gas. This cooling effect helps extend engine life.

Engine exhaust gas is directed to the turbine housing. The turbine housing acts as a nozzle to direct the exhaust gas flow to the turbine wheel blades, where heat energy and pressure from the exhaust gas drives the turbine wheel. The turbine wheel is attached to the shaft assembly along with the compressor wheel, which rotates at the same speed as the turbine wheel. Clean air from the air cleaner, and crankcase vapors from the Crankcase Depression Regulator (CDR) Valve, are drawn into the compressor housing. The air is compressed by the compressor wheel blades and delivered to the engine upper intake manifold. The inside of the turbocharger compressor housing, the compressor wheel, and the inside of the intake manifold can be very oily (wet) due to the crankcase vapors — THIS IS NORMAL.
A vacuum-operated wastegate regulator valve in the turbocharger exhaust housing regulates the flow of exhaust gasses, and the amount of boost delivered to the engine by the turbocharger. The wastegate regulator valve is controlled by the PCM, which monitors turbocharger boost pressure, engine RPM, vehicle load and power requirements. Vacuum is applied to the regulator valve to close the wastegate as increased boost is required. Vacuum is removed from the regulator valve to open the wastegate when increased boost is no longer required.

Vacuum Pump
The belt driven vacuum pump provides vacuum for the operation of the turbocharger wastegate and the Exhaust Gas Recirculation (EGR) valve (L56 only).
The vacuum pump does not require periodic maintenance, and is serviced by replacement.

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