Crankshaft renewing
Arthur Barreto
Co-founder of AP9 Solutions Engineering. Mechanical Engineer, M.Sc . Marine and Power Plants engines.
In the past, four strokes engines were built like two strokes concept, i.e., the framework was formed by bedplate, crankcase (A column) and cylinder blocks tight by tie rods. Nowadays there is no bedplates anymore being the crankcase the housing of the crankshaft and main bearings. Thus, to renew a crankshaft is necessary to upside down the cylinder block to access the main bearings. Depending of the size and weight of the engine is a dangerous task for the fitters specially when performing the repair while vessel is sailing. But there is a way to minimize the risk and reduce the man power. To this we've to use spacers like shown at Figure 1.
At Figure 1 one can see the spacers adjusted, assembled and tight at sump frame base supporting the cylinder block already with the crankshaft removed. The crankshaft was removed by two hand chain pulley blocks positioned at the free and drive end while the crankcase was hold by another hand chain blocks.
Fig. 1 - The cylinder block lifted and secure by spacers (in blue).
When handling the crankshaft we've to avoid excessive deflection due the lashing straps points to not produce stress at shaft. The best way is increase the crankshaft stiffness by use of bolts and nuts in every throw placed like shown at Figure 2 (at place where is placed the deflection dial indicator). The nuts shall be lightly tight and thus the crankshaft can be handled with safety.
Figure 2 - Bolt placed at opposite side to the crank pin inside of crank throw.
For assemble the crankshaft two chain blocks can be used, one at free end and another one at drive end without major risk for the crankshaft integrity.
Figure 3 - Bolts and nuts positioned at every throw.