Monobloc engine

A monobloc or en bloc engine is an internal-combustion piston engine some of whose major components (such as cylinder head, cylinder block, or crankcase) are formed, usually by casting, as a single integral unit, rather than being assembled later. This has the advantages of improving mechanical stiffness, and improving the reliability of the sealing between them.

Monobloc techniques date back to the beginnings of the internal combustion engine. Use of this term has changed over time, usually to address the most pressing mechanical problem affecting the engines of its day. There have been three distinct uses of the technique:

• Cylinder head and cylinder
• Cylinder block
• Cylinder block and crankcase

In most cases, any use of the term describes single-unit construction that is opposed to the more common contemporary practice. Where the monobloc technique has later become the norm, the specific term fell from favour. It is now usual practice to use monobloc cylinders and crankcases, but a monobloc head (for a water-cooled inline engine at least) would be regarded as peculiar and obsolescent.