THE TWIN BEATING HEARTS

The bike that made the GPZ1100 obsolete was the GPZ900R and a totally different beast to its late uncle.

The 900 ran a plain bearing crank not too dissimilar in design to the original superbike – Honda’s CB750/4. Plain or shell bearing motorcycle cranks follow standard automotive practices utilising split con-rods and replaceable white metal-based bearings or shells in the big-ends. These require clean oil supplied at high pressure. The GPZ1100 crank followed Z1/Z900 standard procedure with a pressed-up crank running on roller bearings with a much lower oil pressure. The roller bearing crank makes for an extremely robust bottom-end that’s capable of taking heavy loads and can cope with drastic tuning and/or over bores; it’s also much more forgiving of dirty oil. The downside of the design is that the crank assembly has to be manually trued when pressed together, taking substantially longer to build and thereby costing more to manufacture.

Although Kawasaki stuck with the roller bearing bottom-end from 1972 through to the end of the 1100, they’d taken steps much earlier to ensure a smooth transition to shellbearing cranks in 1976 and reduce assembly costs on future models. The svelte Z650 pioneered shell bearing cranks for the firm and every subsequent derivation of the popular welterweight followed the same path, including the divine Z750 turbo. When the GPZ1100 fell off the sales sheets, Kawasaki pretty much walked away from roller-bearing cranks on all its four-strokes.