Cylinder Block - Combined Block, Head, and Crankcase

Combined Block, Head, and Crankcase

Light-duty consumer-grade Honda GC-family small engines use a monobloc design where the cylinder head, block, and half the crankcase share the same casting, termed 'uniblock' by Honda. One reason for this, apart from cost, is to produce an overall lower engine height. Being an air-cooled OHC design, this is possible thanks to current aluminum casting techniques and lack of complex hollow spaces for liquid cooling. The valves are vertical, so as to permit assembly in this confined space. On the other hand, performing basic repairs becomes so time-consuming that the engine can be considered disposable. Commercial-duty Honda GX-family engines (and their many popular knock-offs) have a more conventional design of a single crankcase and cylinder casting, with a separate cylinder head.

Honda produces many other head-block-crankcase monoblocs under a variety of different names, such as the GXV-series. They may all be externally identified by a gasket which would bisect the crankshaft on an approximately 45° angle.

Exhaust valve failure is common and, owing to the monobloc design, so labour-intensive to repair that the engine is normally discarded.