The purpose of this study is to investigate cause of engine trouble conceming valve-seizure occurred on main engine of Tokyo university of fisheries, the research and training vessel Shinyo Maru. For this purpose, an experimental measurement of the valve stem clearance had been carried out when the valve stem guide was inserted into the cylinder cover. The results showed that the mean value of valve stem clearance reduction was 0.008 mm. The valve stem clearance of measurement value has lowered than the minimum value (0.06.mm) of maker recommendation. It was confirmed that valve-seizure in main engine could cause a dangerous operation. By taking point of view to prevent the engine trouble, these results lead to the suggestion that the valve stem guide should be finished accurately to the desired inside diameter with hand reamer, when the valve stem guide was changed.
