 As competitors produced modern designs, Panther ran into trouble obtaining supplies of Burman gearboxes and Lucas Magdynos, so production ceased in 1966 and the company was wound up.The Panther sloper engine designed by Granville Bradshaw remained unchanged for 25 years and the 650 cc 'heavyweight' had many of the Model 100 components.The increased capacity was achieved by boring out the Model 100 cylinder by 1 mm and increasing the stroke by 6 mm.