Cracks may result from unequal heating due to poor design, bad castings, air pockets in jackets, lack of cooling water and overloading. Modern practice in design and construction has greatly reduced the probability of cracking from the first two causes and watchfulness on the part of the engineers eliminates the other causes, so that cracked heads and cylinders are not nearly so common as they were in the early days of Diesel engineering.
Cracked crank shafts
During the early development period cracked crank shafts were so common that it was considered one of the inevitable hazards associated with Diesel engine operation. This trouble has become very rare, however, in modern practice.
Vibration
The amount of vibration of an engine and of the ship's hull in which it is installed will depend on how well the reciprocating and rotating masses in the engine are balanced and the position of the engine relative to a nodal point in the hull. These are both matters over which the operating engineer has no control. Normally Diesel engines, especially in the large sizes, run with very little vibration but it sometimes happens that an engine will have a critical speed, a speed at which the twisting impulses imparted to the crank shaft by the pressure acting on the pistons coincide with the natural period of vibration of the crank shaft. When the engine operates at this speed violent vibration will occur that may result in loosening nuts, shaking off small fittings, breaking pipes and even breaking of the crank shaft, if continued long enough.
Exercise 1. Answer the following questions.
1) Due to what causes may the engine fail to start on air?
2) How can water get into fuel oil?
3) What is the only remedy against improperly refined oil?
4) What may a distinct loss in efficiency sometimes result from?
5) Why are cracked heads and cylinders not so common as they used to be in the early days of Diesel engineering?
6) What does the amount of vibration of an engine and of the ship's hull depend on?
7) Why was a cracked crank shaft considered one of the inevitable hazards associated with Diesel engine operation?
8) When may violent vibration occur?
Exercise 2. Give the Russian equivalents of the following.
1) Air pocket.
2) To start on air.
3) Starting air valves.
4) Exhaust valves.
5) Unequal heating.
Exercise 3. Use the correct words from the text.
1) Mechanical defects may be due to errors in...
2) There are errors which are difficult to... because they are not expected.
3) A careful... revealed that the engine trouble was due to neglect on the part of the engineers.
4) A thread of waste under the valve caused it to...
5) Stoppage of fuel supply to one cylinder throws extra... on the other cylinders.
6)... of cylinder heads often results from unequal heating.
7) When... of power occurs the first possibility that should be investigated is hot bearings.
Exercise 4. Translate into English.
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1) , , .
2) .
3) .
4) , - , , .
5) , , , .
6) , .
Exercise 5. Make up a dialogue of your own based on the one given below.
THE ENGINE
A.: What type of injection valve is used on modern engines?
.: Modern engines use mechanical fuel injection and the valve is simply a spring loaded check valve with a nozzle on inner end containing one or more fine holes. When the pressure from the pump overcomes the tension of the spring the valve lifts and oil at high pressure is forced through the nozzle as a mist.
A.: What are some of the troubles experienced with injection valves?
.: Leaks, due to grit or scale, burning of valve or seat, sticking of stem in its guide, bending of stem, leaky packing, clogging of atomizer plates and plugging of holes in flame plates or nozzles.
A.: How is a leaky injection valve repaired?
.: Small leaks can be stopped by grinding the valve on its seat with very fine ground glass, carborundum, or prepared grinding compound, finishing up with polishing paste. If seat and valve are badly scored, the valve should be refinished by grinding in the lathe with a tool post grinder and the seat should be reamed, finished up by grinding.
A.: What precaution should be observed in cleaning injection valve stems?
.: Cleaning should be done with kerosene, emery cloth should be used sparingly, or not at all, as it wears away the metal and increases the clearance between stem and guide. If this clearance becomes too great it offers an easy place for gummy oil and carbon to accumulate and the tendency of the stem to stick in the guide is increased.
A.: Why does the exhaust valve require more attention than the inlet valve?
.: Because it is exposed to the action of the very hot gases that flow through it during the exhaust period. These gases may carry hard carbon, grit or scale which tend to cut the valve and seat and the heat tends to warp and burn the valve. The inlet valve passes no hot gas and is cooled by the inflowing clean air during each suction stroke.
A.: What is the best procedure for keeping valves in good condition?
.: Do not wait for trouble to develop before examining valves. Establish a regular routine for removing valves for examination and overhaul. This routine procedure is facilitated, if a complete set of spare valves is available so that the spares can be installed while in port and the used valves overhauled at leisure. The length of time between examinations of valves can be established to suit the nature of the service the ship is engaged in.
Exercise 6. Speak on the following.
1) Derangements likely to occur in connection with starting difficulties.
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2) Derangements likely to occur in connection with water in fuel oil.
3) Derangements likely to occur in connection with improperly refined oil.
4) Derangements likely to occur in connection with loss of power or slowing down the engine.
5) Derangements likely to occur in connection with cracked cylinders and cylinder heads.
6) Derangements likely to occur in connection with cracked crank shafts.
7) Derangements likely to occur in connection with vibration.
