Cylinder Head
DESCRIPTION
The cylinder head cover is made of plastic and includes the blow-by oil vapor separators.
On the top of the cylinder head cover there are mounting surfaces and related cavities for the following components:
- Ignition coils
- Fuel injectors
- Access for the fuel rail mounting brackets
- Blow-by oil vapor recirculation separators
The cylinder head cover has a rubber seal that covers the entire perimeter of the cylinder head interface.
The cylinder head is a one-piece aluminum alloy casting. The cylinder head has the following features:
- Four valves per cylinder.
- The valve guides are press-fit in the cylinder head. A special reamer is used to produce the correct bore size and alignment after installation. The valve guides are not serviceable.
- The exhaust valves are driven directly by the camshaft through hydraulic lifters and rocker arms.
- The intake valves are driven directly by the camshaft through hydraulic lifters and rocker arms.
OPERATION
On the exhaust side of the cylinder head there are mounting surfaces and related cavities for the following components:
- Cavity to allow the exhaust gas to exit from the combustion chamber (turbocharger mounting location).
- Coolant degas lines above the integrated exhaust manifolds (IEM) to evacuate air from the cooling system.
The combustion chambers feature steel inlet and exhaust valve seats.
The cylinder head gasket is a multi-layer steel (MLS) type.
Multi-layer steel or MLS construction consists of two or more embossed stainless sheets riveted to a flat metal core. It is available in one thickness only. Its thickness (when compressed) is 0.78 mm ± 0.055 mm (0.031 in. ± 0.002 in.). They require no additional sealant. Due to the hardness of stainless steel, MLS gaskets require a very smooth finish surface or leaks may result.
The intake valves are steel and have been subjected to a hardening heat treatment and tempering to increase hardness.
The solid valve stem has a nitriding heat treatment of the surface to obtain the highest levels of hardness.
The exhaust valves have to resist higher temperatures than the intake valves and are also subjected to the corrosive effect of exhaust gases. For this reason, the valve head has been made in a different steel alloy than the stem.
The internal cavity of the exhaust valve stem is filled with 45-55% sodium. Sodium becomes liquid at around 100°C (212°F); the liquid sodium allows the heat to be dispersed more efficiently. Sodium in liquid stage moves inside the valve cavity during high alternating motion, transferring part of the high heat from the valve head to the stem (and from there to the cylinder head via the valve guide). In this way, the valve temperature is further reduced.