This paper discribes a new method of cooling exhaust valves for marine diesel engines. The principle of heat pipe is employed to give highly efficient cooling and to improve the durability of valves under corrosive operating conditions. Test valves for two types of marine diesel engines, V52/55A and L60MC, are developed and tested to investigate mainly their performance of heat transfer.
Test results show a sufficient heat transfer capability of the cooled valves without any special design of valve cages, and accordingly a low temperature level at the valve disks. By optimizing the amount and distribution of heat input to the cooling chamber in the valve cone, the valve can be given adequate temperature at any portion, and can be prevented from corrosion.

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Ferrographic oil analyses are made on lubricating oil samples from the fundamental tests using a wear test machine and those from a number of main diesel engines in sererie. The failure scores on ferrous and non-ferrous materials are determined from these analytical results.
The diagnosis method using these scores is applied to actual engines. As the results, it is found that the failure scores are closely connected with the wear conditions of sliding components. In fact, a sign of a failure could be cought before the catastrophic failure of the sliding components.
It is concluded that this diagnosis method by Ferrography is useful to maintain the sliding components of main diesel engines.

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Reducing wear in the engine parts is one of the most improtant themes for study to allow the use of fuel oils of the higher specific gravities and viscosity, and of low combustibility. It could easily be imagined, that huge amount of time and cost are needed to find out optimal combinations from among a great number of conditions through repetitious round of operations conducted for a long period of time.
It order to meet the requirement, the authors had tried to develop a new wear evaluation technique which requies only a short time operation, as a part of the study on the use of degraded fuel oils.
As a result, we have successfully found the method that allows the evaluation of wear rate on cylinder liners and piston rings, which are apt to be affected by the fuel properties, through operations of around 10 hours. The newly developed tecnique has been introduced at the 20th Lecture Meeting, commemorating the 10th anniversary of the organization, and also at the 17th CIMAC Congress. In the present paper, the authors would like to introduce some examples of practical applications of the technique.

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