Notes:
| 1)...without recourse to outside help. | ... . |
| 2) there are conditions, however, under which this becomes impossible. | , , . |
| 3)... and many repairs requiring the engines to be disabled cannot be done.... | ... , , ... |
| 4) in this case repairs are restricted practically to such items as may be carried out at sea. | , . |
| 5) this flexibility seldom results in any injury to the bed itself... | - |
| 6) frames are subject to the same sort of deflection as the bed... | , .... |
| 7)... or what may more precisely be termed | ... , , , .... |
The conscientious engineer who is responsible for the operating efficiency of his ship takes pride in maintaining the machinery in good condition, without recourse to outside help. There are conditions, however, under which this becomes impossible. The operating schedule may be such that the engines must be available for operation most of the time and many repairs requiring the engines to be disabled cannot be done within the short time available for such work. In this case repairs are restricted practically to such items as may be carried out at sea. As the size of marine Diesel engines increases the individual parts become more massive and even routine examinations become too great a task for a small number of engineers and the limited equipment on shipboard. As a result, a large proportion of motorship repairs is done in shipyards. Such repairs may, in general, be grouped into three classes as follows: (1) maintenance repairs, or those resulting from ordinary wear and tear in service; (2) repairs required as a result of faulty design, or changes due to improvements in design; and (3) repairs required as a result of accident, stress of weather, or other unusual conditions.
Bedplates
Most bedplate troubles arise from the surprising flexibility of what is usually a massive structure of cast iron. An example of this was the bed of a 500-hp. engine that had been carefully reset to correct an original misalignment. After accurate alignment was complete and the bed was resting on permanent steel chocks, the spaces between chocks were closed with wooden filler pieces, as is the usual custom in marine work. It was found that a too thick filler piece driven under the bed at about its center with an ordinary hand hammer bowed up the bed enough to throw the coupling on the end of the crank shaft measurably out of line. This flexibility seldom results in any injury to the bed itself, but often has a serious effect on other parts of the engine structure, particularly the crank shaft.
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Framing
Frames are subject to the same sort of deflection as the bed, and in many cases this deflection is caused by the bending of the bed.
Cylinders
Cylinders, or what may more precisely be termed cylinder jackets, give very little trouble, although on some of the older engines an occasional cracked cylinder will be found. Cylinder liners, however, are a prolific source of work for the repair yard. Liner casualties occur either from wear or cracks. Wear is a normal result of engine use, but it sometimes assumes abnormal proportions if operating conditions are not right. Of course, the liner material has some bearing on rate of wear in service and there is some variation in the quality of liner iron found in different makes of engines, but there is not enough variation to make this an important factor in differences in length of liner life found in service. What appears to be the most important factor is the fuel used. Some fuel will contain more abrasive impurities than others, but it is believed that all fuel oil, even the highest commercial grades, should be passed through a centrifuge before being used in the engine.
Exercise 1. Answer the following questions.
1) What does the good condition of the engine depend upon?
2) What repairs can be done at sea?
3) Why are repairs at sea restricted to a certain amount of insignificant items?
4) What does the conscientious engineer take pride in?
5) What are the conditions under which maintaining the machinery becomes difficult?
6) Where is a large proportion of motor-ship repairs done?
7) What do most bedplate troubles arise from?
8) Why should all fuel oil be passed through a centrifuge?
9) Why are frames subject to the same sort of deflection as the bed?
10) What appears to be the most important factor in the length of liner life?
11) How does the quality of liner iron influence the length of liner life?
Exercise 2. Give the Russian equivalents of the following.
1) Operating efficiency.
2) Recourse to outside help.
3) Routine examination.
4) Maintenance repair.
Exercise 3. Use the correct words from the text.
1) The ship has been refloated without... to outside help.
2) He was a conscientious worker and always took... in maintaining his engine in good condition.
3) Under such... repairs at sea became impossible.
4) The repairs required the engine to be disabled but within the short time... for such work it could not be done.
5) The bedplate had to be reset to correct the original...
6) The cylinder liners of this engine give much... and are a prolific source of work for the repairmen.
Exercise 4. Translate into English.
1) , .
2) , .
3) .
4) , , .
5) , .
6) .
7) , .
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8) .
Exercise 5. Make up a dialogue of your own based on the one given below.
ENGINE DAMAGE
A.: Which of the several causes of ignition failures is most
likely to occur?
.: Failure of the fuel supply is the most common cause, for the reason that the fuel pump is very sensitive to the presence of air and unless great care has been exercised in clearing air out of the fuel lines, the pump will not deliver oil to the injection valves. This is especially true after the fuel lines or pump have been opened up for any reason.
A.: How is air cleared out of the fuel lines?
.: Most installations include a by-pass valve in each fuel oil discharge line, adjacent to the injection valve. By opening these valves and operating the hand pumps on the fuel measuring pump, oil is forced through the pump and pipe line and out through the by-passes, carrying the air with it. When only oil flows from the by-passes the valves are closed and a few strokes given to the hand pumps to force some oil into the injection
valves.
A.: How is the compression pressure measured?
.: With the indicator, cutting out one cylinder at a time and indicating that cylinder while the rest of the cylinders operate on fuel or starting air. Both methods should be used in order to determine the difference in compression with hot cylinders and with cold.
A.: How is the compression pressure adjusted?
.: By decreasing or increasing the linear clearance between piston and cylinder head. This is usually done by increasing or reducing the thickness of shims under the foot of the connecting rod.
A.: What are the principal sources of knocks in the Diesel
engine?
.: The large bearings, the valve gear, or the interior of the cylinders. Bearing knocks are caused by too much clearance. Valve gear knocks may be caused by excessive roller clearance, worn or broken rollers, or sticking valve stems. Knocks inside the cylinder are caused by too early injection, excessive lift of air injection valve at low speed, injection air pressure too high, or stuck piston rings.
A.: How is the separation of the two halves of the box usually obtained?
.: By placing sheet metal shims between the abutting surfaces.
A.: How is bearing clearance usually measured?
.: By placing strips of soft lead wire in the bearing and setting up the bolts. The thickness to which the lead wire is mashed will be equal to the clearance.
A.: How is a bearing refitted?
.: By scraping the bearing surface of the boxes with steel scrapers until all the high spots are removed and even contact is obtained between bearing and boxes.
Lesson 6. CYLINDER HEADS
Notes:
| 1)... and as such suffers most from heat troubles. | ... , , , . |
| 2)... but the former is preferred.... | ... ( )... |
| 3)... as is usually the case | ... ... |
| 4)... in years gone by... | ... . ... |
| 1)... that they may be dismissed without discussion. | ... . |
| 2)... may be said to be nonexistent... | ... , ... |
| 3) welding procedure has been developed to the point... | ... |
| 4)... where most cracked pistons can be salvaged at a cost substantially less than the price of a new one. | , . |
The head is usually the most complicated casting on the engine, and as such suffers most from heat troubles. The usual head repair is welding of cracks. Both oxyacetylene and electric welding are used, but the former is preferred if the location of the crack will permit its use. If the crack is near the outer edge of the head, where expansion and contraction stresses can be accommodated, gas welding can be used, but if the crack is near the centre of the head or surrounded by unsymmetrical masses of metal, as is usually the case, electric welding must be resorted to. To make a successful head repair, electric welding must be done very skillfully and studding employed.
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Crank shafts
Breakage of crank shafts in years gone by was accepted as one of the hazards inherent in Diesel-engine operation, but at the present time such breakage is very unusual. Most repair work on crank shafts consists of refinishing pins and bearings that have become scored or worn, or correcting alignment of the shaft in its bearings. Whenever it is necessary to renew a broken shaft, it is found that breakage is due to misalignment of torsional vibration. Wear of main bearings is more rapid in marine engines than in land engines. The more flexible nature of the structure on which the engine rests, as compared to the mass of concrete under the land engine, makes it more difficult to maintain a continuously unbroken oil film between shaft and bearing box.
Torsional vibration is sufficiently well understood that its occurrence can be predicted with accuracy in new engines and steps taken to eliminate it. It is a much less common source of trouble than in former years, but it is found occasionally.
