Connecting rods and crossheads
Connecting-rod repairs are so infrequently required that they may be dismissed without discussion. Crosshead trouble is normally confined to slipper wear.
Piston rods
Piston-rod troubles may be said to be non-existent in single-acting engines that have such rods, but in double-acting designs piston-rod breakage has been rather common.
Pistons
From the repairman's point of view, the piston seems to be the most troublesome of all the major parts of the Diesel engine. The trouble encountered is usually cracking, or wear of ring slots. There are two ways in which cracking occurs: approximately radial cracks develop in the crown or circumferential cracks in the side or skirt. The first is the most common kind, and the appearance of the cracks indicates that it is associated with the phenomenon of metal growth by repeated heating. The second type of fracture, cracks in the sides, is almost invariably due to piston seizure in the liner and is usually associated with cooling-system failure. Welding procedure has been developed to the point where most cracked pistons can be salvaged at a cost substantially less than the price of a new one.
Valves and valve gear
Under this heading there is comparatively little to be recorded. The exhaust valve is the one most frequently in need of repair, due to the fact that a leak usually results in a burned-out valve or seat.
Exercise 1. Answer the following questions.
1) What is the most complicated casting on the engine?
2) What is the usual head repair?
3) Why was breakage of crank shafts accepted as one of the hazards inherent in Diesel engine operation?
4) What does most repair work on crank shafts consist of?
Why is torsional vibration a much less common source of trouble now than in former years?
6) What is crosshead trouble normally confined to?
7) In what engines may piston-rod troubles be said to be nonexistent?
8) From whose point of view does the piston seem to be the most troublesome of all the major parts of the Diesel engine?
9) What repair does the exhaust valve frequently require?
Exercise 2. Give the Russian equivalents of the following.
1) Torsional vibration.
2) Piston seizure
3) Cooling system failure.
4) A burned-out valve.
5) Expansion and contraction stresses.
Exercise 3. Use the correct words from the text.
1) The piston seems to be the most... of all the major parts of the Diesel.
2) The trouble encountered …
3) Wear of main …
4) Connecting-rod repairs …
5) The second type of fracture …
Exercise 4. Translate into English.
1) Предпочтение отдается газовой сварке, если расположение трещины позволяет применить ее.
2) Прежде поломка коленчатого вала в эксплуатации дизеля считалась естественным явлением. Сейчас это редкое явление.
3) Крутильные колебания достаточно хорошо изучены. Их появление в новых двигателях может быть точно предсказано и для их устранения принимаются соответствующие меры.
4) Шатун так редко нуждается в ремонте, что о нем можно и не говорить.
5) В двигателях простого действия, можно сказать, не бывает аварий штоков поршня.
6) С точки зрения ремонтников, поршень доставляет больше всего хлопот.
7) Сейчас методы сварки достигли такого совершенства, что большинство поршней можно восстановить, причем затраты оказываются значительно меньше стоимости нового поршня.
Exercise 5. Make up a dialogue of your own based on the one given below.
ENGINE DAMAGE
A.: What is the best method of keeping a check on crank shaft alignment and main bearing wear?
В.: By the use of a bridge gauge, on which are stamped the heights of the crank shaft at the main bearings at the time the engine was installed. Periodical measurements with this gauge, compared with the original measurements, will indicate any dropping of the shaft.
A.: How are the cylinders lubricated?
В.: By means of small oil pumps, assembled into multiple units called mechanical oilers, which are operated by linkages from any convenient moving part of the engine. These pumps feed the oil in drops, at a rate that can be regulated by small adjusting screws, into small pipes leading to the cylinders.
A.: For what other purpose is the compressor used besides supplying injection air?
В.: The compressor always has a capacity in excess of the amount required for spraying the fuel. The excess air is bypassed into the starting air tanks to supply air for starting the engine.
A.: Why is the injection air usually compressed in three stages instead of one?
В.: Because the temperature at the end of a single compression would be excessive. By performing the compression in three stages the air can be cooled after each stage in the compression. In this way the heat is easily handled and the amount of power required to compress a given quantity of air is greatly reduced.
Exercise 6. Speak on the following.
1) Shipyard repairs of cylinders and cylinder heads.
2) Shipyard repairs of crank shafts.
3) Shipyard repairs of pistons.