[File:De Dion-Bouton engine (Rankin Kennedy, Modern Engines, Vol III).jpg|thumb|De Dion-Bouton engine with monobloc cylinder heads, c. 1905]] A monobloc or en bloc engine is an internal-combustion piston engine where some of the 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 also improving the reliability of the sealing between them.