| January | — | — | Rocker arms drilled for oil flow to adjusting screw, oil deflector rings added to valve stems, shorter valve guides |
| January | — | — | Rocker arms drilled for oil flow to adjusting screw, oil deflector rings added to valve stems, shorter valve guides progressively sprung valve springs |
| January | — | 126 001 | Rocker arms drilled for oil flow to adjusting screw, oil deflector rings added to valve stems, shorter valve guides #1 bearing journal play increased |
| February | — | — | #1 bearing journal play increased |
| February | — | — | rocker shaft stud modification |
| February | — | — | heavier connecting rods |
| March | — | — | rocker shaft stud modification heavier connecting rods |
| March | — | 128 230 | Oil strainer plate held on with cap nuts, better gasket material |
| April | — | 128 551 | different connecting rod screws |
| April | — | — | Oil strainer plate held on with cap nuts, better gasket material oil pump cover gasket better material |
| April | — | — | oil pump cover gasket better material |
| April | — | — | different connecting rod screws |
| May | — | — | Oil strainer plate held on with cap nuts, better gasket material oil pump cover gasket better material different connecting rod screws |
| June | — | 131 725 | connecting rod torque lowered |
| June | — | 131 651 | rotocap valve rotating device for up to 2500RPM |
| July | — | — | connecting rod torque lowered |
| July | — | — | larger oil filler hole and cutout in web below |
| August | — | 132 927 | larger oil filler hole and cutout in web below |
| August | — | 133 001 | main bearing #1 clearance increased |
| August | — | — | larger oil filler hole and cutout in web below main bearing #1 clearance increased valve spring tension increased |
| September | — | 133 921 | rear main seal - different shape and material |
| October | — | — | oil intake pipe secured to sump plate stud |
| October | — | — | rear main seal - different shape and material oil intake pipe secured to sump plate stud valve spring tension increased square boss heads |
| October | — | 135 938 | oil intake pipe secured to sump plate stud |
| October | — | — | square boss heads |
| November | — | 136 980 | rocker arms - top oil drilling welded up |
| November | — | — | 004� valve adjustment sticker added |
| November | — | — | rocker arms - top oil drilling welded up |
| November | — | — | 004� valve adjustment sticker added |
| December | — | 139 276 | lifters- smaller diameter contact flange |