Global 700cc Engine for  Next-Generation

About the Global 700cc Engine for Next-Generation

  • Introduction
  • Technical details

Technical details

1. Liquid-cooled, OHC, in-line, 2-cylinders with forward leaning angle of 62º(Engine mounting angle) : Uneven-interval firing produced by a 270º phase crank

The development team wanted to create a medium-displacement motorcycle with "an engine that was not about absolute performance, but about enabling users to fully enjoy the profound sensation of powerful low- and mid-range tourque without feeling any stress." To this end, the team decided on the following concept:

In pursuit of a ride to suit mature tastes, aim for a lightweight, compact engine layout

The pursuit of this concept was to result in a hitherto unknown ride sensation and "a compact, new value engine that delivers a world-class environmental performance." To achieve a "ride to suit mature tastes," development began with discussions about the basic layout. In-depth discussions took place to determine what kind of engine would deliver the desired characteristics. Topics discussed at length included displacement, the number of cylinders (one to four cylinders), engine type (single cylinder, in-line, V-shaped, horizontally opposed/OHC, DOHC) and alancers (primary-secondary balancers, coupling balancer). In the end, it was concluded that the optimal engine to achieve the goal would be a liquid-cooled, in-line, 2-cylinder, 700cc, OHC engine with an 62º (Engine mounting angle) forward lean.

Scond-generation Dual Clutch Transmission Cut engine model

To concretely arrive at a "ride to suit mature tastes," a choice had to be made between even and uneven firing intervals. Uneven-interval firing with a 270º phase crank was chosen over orderly and smooth even-interval firing in order to achieve a throb close to that of a 2-cylinder V-engine, because this would result in an emotional yet comforting means of daily transportation.

Uneven-interval firing Comparison image

The engine design employs the 270º phase crank technology already filed by Honda in 1985. Because of the crank's 270º phase, manufacture using conventional top-and-bottom-half techniques generates considerable waste in the crank web section. Furthermore, because the crank web section is difficult to fully machine, this method produces a heavy crank, which was not consistent with the development concept and would have resulted in cost increases.

 Cross sectional view of 270º phase crank engine
270º phase crank

To resolve this issue, the development team undertook the challenge of manufacturing a "twisted crank." The team's manufacturing method involved forging the top and bottom halves of a crank at 360º to keep waste to a minimum, and then, before the crank journal portion cooled down, immediately twist it an additional 90º, to make the angle 270º.
This "crank-twisting" method of manufacture had already been successfully used to add a 60º twist to the crank for Honda's 6-cylinder V-engine used in automobiles. Collaboration between engineers in Honda's automobile and motorcycle R&D centers meant it was possible to build the technology for a 90º twist and as a result successfully avoid cost increases by producing, without machining, a lightweight crank web with an optimal balance.

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