Actions to be Taken for Slack Holding Down Bolts
When the chocks and their mating surfaces on the bed plate and tank top have fretted, the chocks cannot properly support the engine. If the holding down bolts are tightened, the crankshaft alignment may be seriously affected, with lesser effects being felt on cross head guide and cylinder alignment.
The seriousness of the situation will be depend on the amount of fretting that has occurred. Before any tightening of the holding down bolts is carried out, the alignment of the crankshaft should be checked, by taking deflections with a dial gauge.
If the crankshaft alignment is satisfactory, the slack chocks can be removed and smoothed on the mating surfaces and replaced. The bolts can then be tightened to harden the chock.
After all the walls and chocks have been tightened, the crankshaft alignment must be rechecked.
Reference
“Marine Engineering Practice” by Vikram Gokhale and N. Nanda