Determining Overhaul Timing - Mitsubishi L Series Service Manual

DETERMINATION OF OVERHAUL

1. Determining overhaul timing

In most cases, the engine should be overhauled when the compression pressure of the engine becomes low. An increase in
engine oil consumption and blow-by gas are also considered to evaluate the engine condition. Besides, such symptoms as a
decrease in output, increase in fuel consumption, decrease in oil pressure, difficulty of engine starting and increase in noise are
also considered for judging the overhaul timing, although those symptoms are often affected by other causes, and are not
always effective to judge the overhaul timing. Decreased compression pressure shows a variety of symptoms and engine
conditions, thus making it difficult to accurately determine when the engine needs an overhaul. The following shows typical
problems caused by reduced compression pressure.
(1)
Decreased output power
(2)
Increased fuel consumption
(3)
Increased engine oil consumption
(4)
Increased blow-by gas through the breather due to worn cylinder liners and piston rings (Visually check the blow-by
amount)
(5)
Increased gas leakage due to poor seating of inlet and exhaust valves
(6)
Difficulty in starting
(7)
Increased noise from engine parts
(8)
Abnormal exhaust color after warm-up operation
The engine can exhibit these conditions in various combinations. Some of these problems are directly caused by worn engine
parts, while others are not. Phenomena described in items (2) and (6) will result from improper fuel injection volume, fuel
injection timing, worn plunger, faulty nozzles and also faulty conditions of electrical devices such as battery and starter. The
most valid reason to overhaul an engine is a decrease in compression pressure due to worn cylinder liners and pistons, as
described in item (4). In addition to this item, it is reasonable to take other problems into consideration for making the total
judgement.
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