Exactly which model are we talking about? There's 359cc, 539cc, 800cc, 797cc, 539cc, 547cc, 657cc, 658cc, 970cc, 1,298cc, 1,324cc, 1905cc (probably not this one, if you reckon its small

), and more. Even a year would narrow things down a lot

.
My mechanical knowledge is limited, but you may find a motorcycle engine and a big hammer is your best option.
EDIT: Plus there's both two and four stroke models.