| January | — | 150 262 | Oil strainer plate, oil drain threads has shoulder for sealing oil pickup tube no longer angled on the end |
| January | — | — | Oil strainer plate, oil drain threads has shoulder for sealing oil pickup tube no longer angled on the end |
| January | — | — | piston pin bushing now steel backed lead bronze coated |
| January | — | — | Oil strainer plate, oil drain threads has shoulder for sealing oil pickup tube no longer angled on the end piston pin bushing now steel backed lead bronze coated |
| March | — | 152 806 | distributor drive shaft - teeth extend full length |
| March | — | — | distributor drive shaft - teeth extend full length |
| March | — | — | tighter connecting rod installation tolerance reinforced oil cooler mounting tabs on case |
| March | — | — | distributor drive shaft - teeth extend full length |
| May | — | 154 093 | O-ring on flywheel replaces metal gasket |
| May | — | 154 032 | longer gland nut threads |
| May | — | — | O-ring on flywheel replaces metal gasket, longer gland nut |
| July | — | — | pushrods now slightly thicker and longer |
| August | — | 155 969 | Self lock/sealing nuts on center M12 case studs |
| August | — | — | Self lock/sealing nuts on center M12 case studs |
| August | — | — | pushrods now slightly thicker and longer |
| September | — | 156 976 | pushrods now slightly thicker and longer |
| October | — | 157 265 | crankcase now has 0-rings on M12 studs |
| October | — | — | crankcase now has 0-rings on M12 studs |
| October | — | — | larger contact area for M12 studs |
| October | — | — | crankcase now has 0-rings on M12 studs |
| October | — | 157 980 | larger contact area for M12 studs |
| November | — | 157 226 | oil pipe now seamless |
| December | — | — | oil pipe now seamless |
| December | — | — | oil pump cover gasket different |