4-stroke and 2-stroke diesel engines both use the principles of internal combustion, so many of their components have similar designs.
Diesel engine components are exposed to higher operating temperatures, pressures and forces than gasoline engines of similar size. Their compression ratios are higher, and they are often designed to out-last gasoline engines. Their engine parts are usually heavier or more rugged than those of similar output gasoline engines.
Diesel blocks are usually made of cast iron, and heavier than in a gasoline engine. The skirt of the block usually extends below the centerline of the crankshaft. This adds strength and rigidity.
Machined into it are the cylinders which are usually in the form of detachable sleeves or liners.
It is sealed at one end by a deep-section piece of metal or alloy called a cylinder head, which houses the valves and injectors.
Most cylinder heads in diesel engines are cast iron. Depending on the engine design, single or multiple heads can be used.
Multiple heads avoid large castings that, apart from being heavy, are liable to distortion.