The periodic maintenance method is well known as one of the best methods in the preventive maintenance. Its properties in the strictly periodic maintenance have been studied theoretically, but the case where there is randomness in the periodic maintenance interval has never been investigated so far. On the other hand, the field maintenance data have suggested us difficulties of keeping the interval of periodic maintenance strictly.
Therefore, this paper deals with the characteristics of the MTBF (Mean Time Between Failures) under the periodic maintenance with random interval. First we choose a Weibull distribution as the reliability function of the items and next set up the maintenance model which exists the random interval in the periodic maintenance. Under these conditions, we investigate how the randomness of the maintenance interval effects on the MTBF of the items from the theoretical viewpoints. Finally, we show the usefulness on the basis of results obtained here.

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Engine performance and exhaust gas emissions are affected by wear of exhaust valve and seat. In this paper, an analysis of relative slip between the contacting surfaces is carried out to examine the wear mechanism, as the first report on wear of valve and valve seat. In addition, a laboratory test-machine is designed to simulate the wear produced by marine diesel engine. The results show that micro-slip is generated between the seating surfaces by elastic deformation of the valve system resulted from the high combustion pressure. The magnitude of the slip is dependent on the coefficient of friction and the seat angle. The test-machine is found to be useful to examine the detail of wear phenomena with a little improvement.

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The first three of the authors have developed a new technology for semi-permanent use of lubricating oil and no waste oil. The technology is called kidney system and has been widely used in marine and cogeneretion diesel engines. In orger for a kidney system to work well, it must be installed on a clean engine. Therefre, an old engine which has been in service for many years must be perfectly cleaned before it is equipped with the kidney system. This paper first reports that engines are not cleaned at all by the conventional flushing system. It also reports that the authors have developed a new flushing system which enables it to clean old used engines almost perfectly about in two hours. The new flushing system has been increasingly used in practice in order to clean old used engines and to equip them with the kidney system for saving lubricating oil and no waste oil.

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In the 2-stroke diesel engine power plant, application of SCR (Selective Catalytic Reduction System) in between engine's cylinder exhaust gas outlet and the turbo-charger is one solution to get higher NOx reduction rate.
In this case well know phenomena is unstable engine operation due to rather large heat mass of the SCR, specially during engine load up and down program.
This paper shows that this phenomena is soluble by installing exhaust gas extract valve and adequate active valve control, also shows the outline of mathematical anlytic evaluation model and the test results on the actual power plant.

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