Mitsubishi diesel engines Service Manual page 39

OVERHAUL TIMING
1. Identifying the Timing for Overhaul
Generally, when the compression pressure has dropped below the specified value, overhaul of the engine
needs to be considered. Other parameters should also be considered in making the decision as to whether or
not to overhaul the engine, such as engine oil consumption and blow-by gas volume.
Some of the phenomena that may suggest, but are not necessarily the criteria for, the need to overhaul the
engine include reduced power, increased fuel consumption, oil pressure drop, difficulty in starting and higher
noise level.
More specifically, reduction in compression pressure creates various types of phenomena in various
combinations, and this is why it is difficult to make a correct decision. Typical phenomena include:
(a) Reduced power
(b) Increased fuel consumption
(c) Increased engine oil consumption
(d) Increased blow-by gas through the breather due to worn parts such as cylinder liners and pistons
(e) Increased blow-by gas due to poor seating of inlet / exhaust valves
(f) Poor starting
(g) Increased noise levels of various engine parts
(h) Abnormal color of exhaust gas after warm-up
Some of those listed above are directly related to the deterioration of the engine and some are not.
Items (b) and (f) are heavily influenced by fuel injection pump displacement, fuel injection timing, wearing
of plungers, nozzle conditions, and conditions of electrical equipment such as battery and starter.
The most reliable criterion for engine overhaul is reduced compression pressure due to the wearing of
cylinder liners and pistons [item (d)]. This should be combined with other items for comprehensive review
to reach a rational conclusion.
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