The marine diesel engine crankshaft can be classified as:
- Fully built
- Semi built
- Welded crankshaft
- Solid single piece- used in very small engines
Are those in which all the various components are shrink-fitted after separate fabrication. On older engines the so called fully built method was used. This consisted of forging separate webs, crank pins and main journals. The crank pins and journals were machined and matching holes bored in the webs, which were slightly smaller in diameter. The webs were heated up and the crank pins and journals fitted into the holes (which due to the heat had expanded in size). As the webs cool down, so the diameter of the bored holes would try and shrink back to their original size. In doing so, the crank pins and journals would be gripped tightly enough to stop them being able to slip when the engine was being operated normally. One way to ensure that the shrunk fit is stable is to have a dowel pin but this would act as a stress riser and is unacceptable.
FIG.: FULLY BUILT CRANKSHAFT