The Concept: An OHV + Inclined Cylinder that Changed the World of General Purpose Engines
Most general purpose engines were in those days of the SV type. Accordingly, new OHV engines were expected to give the edge to Honda, since SV engines consumed more gasoline and oil, and were noisy and hot. In addition, they had shown themselves to be subject to problems in initial quality. The OHV configuration, on the other hand, was more powerful, economical, cleaner, quieter, and more durable. However, despite the OHV's obvious benefits, the SV configuration remained the mainstream in general purpose applications.
A local market-compatibility test for the ZE Series model CX140, held in Thailand (Photograph on those days courtesy of Yoshinobu Yamaguchi)
The reasons for that were as follows:
First, the OHV engine was larger because its valve had to be mounted above the cylinder. The OEM companies would not accept any engines exceeding their standard installation dimensions, which were for the most part based on SV engines. To find a market, a general purpose engine had to ensure "installation compatibility.
Second, the larger number of parts made the OHV heavier and more costly. Portability and economy are basic requirements in the world of general purpose engines. No matter how well one might perform, no engine would be accepted as a commercial product if the basic requirements - again, portability and economy - were not satisfied. For these reasons the OHV engine design had been studied by most manufacturers, but never seriously developed.
The ZE5 lawn mower engine would have a certain amount of latitude in dealing with these characteristics, because it was developed as part of a complete machine. However, the ZE01 general-purpose engine targeting OEM companies found itself up against a wall. The problems of size, weight, and cost necessitated engineering targets that had to be achieved in order to develop a successful product. Such problems also meant they would have to depart from common sense thinking with regard to general purpose engines.