A fusion machine which can be top-loaded on very large polyolefin pipes and pipelines has jaws which consist of an upper half jaw and lower left and right complemental jaws which pivot on the half jaw. Left and right actuators connected between the complemental jaws and the half jaw operate in one direction to cause the complemental jaws to rotate to an opened condition in which the upper half jaw can be lowered onto and lifted from the pipes to be fused and in the other direction to cause the complemental jaws to rotate to a closed condition in which the pipes to be fused are gripped so substantially around their circumferences as to resist their deformation from round during manipulation by the machine. The top-loading machine minimizes the need for heavy equipment to load and unload pipe to and from the fusion machine.