1. Purpose
1) Cylinder head is used to seal the top of cylinder liner, formed airtightoperating space with piston and cylinder liner.
2) Fix cylinder liner tightly to the proper position of the machine, and makepiston operate properly.
3) To install various accessories of diesel engine, such as oil burner nozzle,intake and exhaust valve unit, cylinder starting valve, indicator valve, safetyvalve, valve arm, etc.
4) Lay out admission and exhaust passage, coolant gallery, etc. also lay outswirl-chamber and pre-combustion chamber in cylinder cover of compact andhigh-speed machine. So there are so many bores and passages in cylinder coverto form its complicated structure.

2. Requirements ofcylinder liner
It should have high strength, good heat resistant and excellent mouldingtechnique.
Structure of cylinder cover should be enough harden; shape of fire exposedsurface should be in accordance with drawing requirements, with enough smoothand complete circular transmission. Compression face and various channelsshould conform to pressure requirements, size and shape of seating must meetprecision requirements. Particularly, every seat bore and cone valve keep agood condition of sealing. Most of cylinder cover with less than 400mm of cylinder diameter adopts gray castiron like HT400, while adopts spheroidal graphite cast iron such as QT60-2 forthose more than 400m. Manylarge-scale and low speed diesel engines use cast steel cover or cast iron –cast steel combinatory cover.