Cylinder Head Assembly: Description and Operation

Cylinder Head


the cross flow design cylinder head includes a single overhead camshaft, two rocker shafts and four valves per cylinder. the valves are arranged in two inline banks, the intake side facing towards the radiator, the exhaust facing towards the firewall.

Camshaft
the camshaft is machined from nodular iron. Nodular iron combines many advantages including good cast ability, excellent machinability, wear resistance, and weight savings.
the camshaft consists of 5 bearing journals and three valve lift lobes per cylinder. the camshafts are identical for both derivatives. the intake side uses one rocker per valve, while on the exhaust side a single rocker operates both valves.
A machined recess in the cylinder head next to the Number 5 camshaft journal controls the camshaft end float.
the camshaft retaining pedestals support both rocker shafts.

Rocker Arms and Rocker Shafts



the rocker shafts are hollow to allow an oil supply to the hydraulic lifters that are retained in the end of the rocker arm. the valves are opened by roller rocker/hydraulic lifter assemblies, which pivot on the rocker arm shafts.


Valves
Powder metal valve guides and seats are installed on both engine derivatives, the valves, springs and retainers are of conventional design.


Intake Valves
the intake valves are made from carbon steel. the carbon content allows the valve to be hardened and tempered to increase strength and also to be locally hardened to improve wear resistance. the MINI COOPER S uses an upgraded material.

Intake Valve Seat Inserts
Powder metal technology is used for valve seat inserts as the sintered part requires little or no machining and any number of material compositions can be developed to satisfy particular engine demands.

Exhaust Valves
the exhaust valve specification is austenitic steel, a particular type of steel with characteristics that are ideal for exhaust valve manufacture. the MINI COOPER S has upgraded exhaust valves.

Exhaust Valve Seat Inserts



Many of the characteristics for the intake valve seat inserts carry over to the exhaust valve seat inserts. In addition, the exhaust valve seat uses what is known as "Grade J" steel, this contains molybdenum and tungsten. This provides high heat hardness giving increased resistance to indentation and wear.