at an angle of approximately 3 u00b0 the forward ends of side rails 12 are joined to a special front frame portion 16 which is generally v shaped in plan and includes a pair of side sections 18 a front plate 20 and a forward bottom plate 22 see fig7 each side section 18 has a plate like rear portion 18a and a forwardly tapering beam like portion 18b the portions 18b are preferably constructed by overlappingly welding together two channel sections in a manner similar to that described in connection with the construction of side rails 12 as illustrated in fig2 the side sections 18a being of greater depth than side rails 12 overlap the forward portions of the respective side rails and extend forwardly and upwardly therefrom each side section 18 is bent inwardly about a substantially vertical axis as at 21 at an angle of approximately 20 u00b0 relative to the side sections 18 a the two beam like forward portions 18b gradually approaching one another as they extend forwardly front plate 20 is joined to the undersides of portions 18b and the generally triangular bottom plate 22 continues forwardly of front plate 20 and is disposed beneath the foremost parts of the portions 18b the joints between the foregoing components are preferably made by continuous welds a vertical bearing 24 is carried on front frame portion 16 between the forward ends of the beam like portions 18b bearing 24 rotatably receives a substantially upright.