Q.671 Which of the following statement concerning cylinder liner wear is true?Ans. (b) Excessive liner wear causes the wear the between the piston ring and the grooves.Due of excessive and non-uniform liner wear, the piston rings will try to maintain the contact with the liner wall. As a result, there is continuous radial movement of the piston rings over the groove in the piston because of which there will be friction between the piston rings and the groove. Hence the bottom of the groove will get worn out faster if the cylinder liner is worn out excessively and non-uniformly.

Q.672 Generally where you should find the greatest amount of wear on the cylinder liner?Ans. (c) Opposite the top ring shortly after the piston travel has ended the compression stroke.The liner wear is maximum when the piston is at TDC. It is time when the piston is subjected to high temperature and low lubrication. As a result, the cylinder liner is worn-out excessively along with the piston rings because of the excessive pressure between the liner and the piston rings and lack of lubrication due to high temperature.

Q.673 Worn main bearing will cause the compression ratio of an auxillary diesel engine Ans. (b) to decrease.When the main bearings are worn out, automatically the crankshaft inorder to keep contact with the bottom half of the main bearing will try to sink downwards. Due to this, the clearance volume between the piston and cylinder head, when the piston is at TDC, will increase. This will cause the loss of compression pressure.

Q.674 Insertion shims in the main marine diesel engine between the connecting and the bearing box would result in Ans. (a) increase in compression ratio.The marine type of connecting rod has a * and if that * is fitted over the bottom end bearing housing and by inserting the shims between the palm and the bearing housing automatically the piston is raised up and when the piston is raised up the compression ratio increases

Q.675 Diesel engine crankshaft deflections are taken at four crankshaft positions. Good engineering practice require the deflection gauges are indicated to be Ans. left in place for all four readings.When the crankshaft deflection is taken it is done at four position of the piston. As a matter of fact actually five positions of piston. During this, we are checking the distance between the two webs. Inorder to check the distance between the two webs, it is necessary that the dial gauge fitted between the two webs should be continuously kept in position to get the correct reading all around the cycle.

Q.676 An acceptable method of measuring the correct rotational force applied to the connecting rod and main bearing bush is to use a Ans. torque range.

The tightening of the bottom end bearing bush can be done safely and properly by use of torque range. It has got silicon clutch and hence it will never get overtightened. When a particular torque is reached it will give a sound which will indicate proper tightening without over stressing or over tightening of the bolts. Hence torque range is the better method of tightening the bottom end bearing bolts. At present, there are other methods such as angle and hydraulic methods which are much better than the torque method.

Q.677 Small cracks in the surface of diesel engine crankshaft bearings are an indication of Ans. fatigue failure. When the crankshaft bearing is subjected to fatigue, the strength at which it will crack will lower down and hence the cracks appear. These cracks are quiet significant and are not because of corrosion or insufficient lubrication or abnormal wear. This will not give the cracking. Cracking is due to the material which is under stress due to fatigue.

Q.678 If water is found in the crankcase of a diesel engine the cause may be Ans. due to cracked cylinder head, cracked cylinder liner and leaky cylinder gasket.In case of four-stroke engine if the cylinder head is cracked, there is a possibility that water may enter the crankcase when the engine is in stopped condition. If the cylinder liner is cracked water may enter from the cylinder head through the gap between piston rings and it will enter into the crankcase.

Q.679 Diesel engine piston ring blowby is usually caused by Ans. excessive ring clearance at the ring gap Ring gap clearance is also called as butt clearance. If this butt clearance is excessive, it finds an easy assess for the hot and high pressure gases to pass through and it will give more amount of blowpast

Q.680 Diesel engine blowby into crankcase is caused by Ans. excessive ring gap clearance.

Q.681 The wear is usually greatest at the top of the cylinder in a diesel engine due to Ans. the highest pressure being exerted.At the TDC, when the fuel is injected, high pressure is developed. This high pressure finds its way behind the piston rings and they are forced against the liner walls with great contact pressure and thus more amount of weardown will take place. At the same time, near TDC because of the high temperature, the lubricating effect is reduced and hence there is more amount of wear of the liner and the piston rings.

Q.682 Which of the following operation will have a direct impact on the rate of wear of cylinder liner?Ans. (b) Quality of the fuel injected.If the quality of the fuel injected is bad i.e. it has more amount of sulphur or vanadium or sodium or abrasive particles, excessive wear down of the liner will take place due to corrosive effect. At the same time, the wear down may also take place due to abrasive effect.

Q.683 Failure to remove the carbon ridge from the top of the cylinder when replacing the piston ring will result in Ans. damaged upper piston ring and the ring landing surface. If the carbon ridge is not removed and new piston rings are replaced, the top most ring will hit at the ridge and may get damaged. At the same time, it will damage the ring landing surface. Hence it is necessary to grind off the ridge when the piston is removed and the rings are replaced (repressed).

Q.684 Scuffed cylinder liner bearing surface in a diesel engine can result from Ans. (c) operating the engine on overheating.When the engine is operating on overheating condition (which can exist due to blowpast), the lubrication between the piston and the liner is not effective because the lubricating oil will evaporate faster. Under such circumstances, because of loss of lubrication oil, the sliding friction between the piston and liner walls will cause great amount of heat which will ultimately cause the scuffing of the liner walls.

Q.685 Water accumulation in the cylinder of a secured engine will indicateAns. cracked cylinder liner.When the engine is secured, i.e. it is standstill, if there is water accumulation on the top of the piston it is an indication that the liner is cracked or the cylinder head may be cracked. Hence there is a possibility that water may get accumulated on the top of the piston through these cracks.

Q.686 The formation of carbonmonoxide in diesel exhaust gas can be reduced by Ans. (c) maintaining proper combustion and scavenging.Carbonmonoxide gas is produced because of lack of oxygen during the burning process. Hence if proper combustion and scavenging process is maintained, fuel will burn efficiently and because of proper scavenging the amount of air will be sufficient and hence better combustion and no starvation and no formation of carbonmonoxide.

Q.687 The amount of wear on a speed precision main bearing can be accurately determined by comparing the data from previous reading to the present reading taken with ball anvil outside micrometer.Ball anvil outside micrometer can be utilized to measure the thickness of curved surface. So by comparing the thickness (previous and present) of the shell bearing, we will be able to find out the degree of wear of the bearing.

Q.688 On diesel engine equipped with individual jerk type fuel pumps, adjustments should be made to the tappet push rods of the pump to Ans. equalize effective delivery stroke.The effective delivery stroke of all units can be equalized when the upward moving plunger will close the suction ports of all the fuel pumps at the same crank angle. This can be achieved by adjusting the tappet of the plunger under the jerk pump so that the effective delivery stroke can be adjusted equally.

Q.689 The amount of wear on a split fixed sleeve type main diesel bearing can be accurately determined with aAns. (c) ball anvil outside micrometer. (ALREADY DISCUSSED)

Q.690 Friction, engine wear, and oil consuming in a diesel engine are directly related to theAns. viscosity of the oil.In case of lubricating oil, viscosity of the oil place an important role in reducing the friction wear and wear down of different components of the engine because the formation of film lubrication depends on the viscosity of the oil. The viscosity of oil has to maintained in a preset condition so as to have proper film thickness and to reduce the friction between the rotating parts and to take out the heat generated due to friction. Hence viscosity plays an important part in determining the engine wear and friction. At the same time, if the viscosity is too low there is possibility that excessive consumption will take place because of leakage of oil and more amount of evaporation will take place.

Q.691 Improper cooling of diesel engine cylinder liner due to the accumulation of scale deposits may causeAns. increased piston ring wear. When the liner wall temperature is high, the lubrication between the liner and piston will get evaporated. Hence less amount of lubrication oil film will be there between the liner and piston rings thus causing excessive friction between liner and piston rings causing excessive weardown of the piston rings.

Q.692 The nuts of main bearing, connecting rod bolts and all other moving parts are to be secured by Ans. split pins or other effective means.All the nuts of these parts after tightening should be locked by means of locking washers, star washers or split pins so that they will not tend to loosen out. This is a safety measure in addition to hydraulic tightening.

Q.693 The easiest way to locate a defective diesel engine exhaust valve isAns. by comparing the exhaust pyrometer readings.By comparing the exhaust pyrometer readings, leaky exhaust valves can be easily detected because exhaust gas temperature will be high. It will be on the continuous rise and it will indicate that the exhaust valve is leaking. This could be found out by taking a compression and peak pressure curves where we find that both the compression and peak pressure curves for that particular unit is reduced.

Q.694 Engine coolant accumulating in diesel engine lubricating oil can result from a Ans. cracked cylinder head or liner.The cooling water finding its way into the engine lubricating oil in the crankcase is only possible because of the cylinder or liner crack or the O-ring which seals the space between the liner and cylinder block are leaking and hence water is finding its way into the crankcase.

Q.695 If it becomes necessary to clean the spray holes in a diesel engine fuel injector Ans. you should use a suitable sized * wire and carbon solvent.The carbon solvent will dissolve the hard particles around the holes. Hence the hard particles because of which the holes are clogged get dissolved and it would be easy to remove the dissolved carbon particles by use of wire and hence carbon solvent is necessary to clean the clogged spray holes.

Q.696 While over-oiling a jerk type fuel pump it is necessary to replace pump plunger which of the part listed below must also be replaced?Ans. pump barrelThe pump barrel and plunger are lapped together and they form a single unit. They cannot be replaced individually because perfect surface finish can be achieved between the two surfaces. Hence it is not possible to replace them individually. If it is necessary to replace the plunger the barrel also has to be replaced.

Q.697 An acceptable means of tightening connecting rods and main bearing cap bolts is (a) to measure the torque applied to each nut and bolt assembly(b) stretch up each nut before and after tighteningAns. (a) to measure the torque applied to each nut and bolt assembly. The torque should be measured so that they are tightened to the required torque and they will not be overtightened. Hence it is necessary to measure the torque applied to each bolt at the time of tightening. At the same time, the elongation can also be checked to countermeasure to confirm the proper tightening.

Q.698 In a diesel engine when refitting piston rings you should (a) change the ring gap at the smallest diameter of the cylinder liner(b) remove carbon from ring groovesAns. both (a) and (b). When fitting new piston rings it is necessary to check the butt clearance and that is possibly checked by fitting the rings at the least worn out position of the liner and checking the gap at the end of the piston rings. At the same time it is necessary to make sure that the ring groove is properly cleaned and there is no dirt or carbon deposits in the groove otherwise the rings will collapse and blowpast will take place. Hence it is necessary to check both i.e. the ring gap and carbon deposits.

Q.699 Problems with the diesel engine fuel injection pumps are usually caused byAns. (b) contaminated fuel.When the fuel is contaminated with water or insoluble hard particles under, the fuel pump plunger and barrel will get excessively wornout because of the abrasive wear and the corrosive wear and all the problems related to the jerk type pump will start from here onwards.

Q.700 Dirt lodged on the nozzle valve seat of a fuel injector nozzle will causeAns. (c) fuel leakage after and before injection.

If the dirt will be lodged at the seat, the seat will not be leak-proof. Hence whenever there is low pressure inside the cylinder liner or in combustion space, oil will leak from the seat and it will drip in the combustion space thus causing the high exhaust temperature and loss of power.

Q.701 When a diesel engine is operated having a piston ring cold gap clearance less than that recommended by that manufacturer, the ring willAns. seize and buckle.If the ring gap clearance is less, the ring will expand. Thus ends of the rings will butt against each other hard. As there is no way to expand, the rings will expand radially and ultimately the rings will crack and it will collapse and break. At the same time, due to the excessive heat, which is generated due to pressure between the piston and the liner, the piston ring will get seized inside the liner.

Q.702 Due to excessive water in the fuel diesel engine fails to start. Before engine is started the water must be removed from the fuel pump fuel stainer.If excessive water is developed in the fuel in that case the engine will not start. In that case, it is necessary to remove the water from the fuel oil at settling tanks, service tanks through the filter so that when fuel injection starts the engine will pick up on fuel immediately.

Q.703 Failure to remove the carbon ridge at the top of the piston while removing the piston may result inAns. seizure of piston and rings inside the liner.It will be difficult to remove the liner due to the carbon ridge at the top which results in the seizure of the piston and rings. Hence it is necessary to grind the carbon ridge in order to facilitate the removal of the liner. Otherwise, the top most ring will get jammed up between the ridge and hence the liner may come out with the liner or the piston may get jammed up in the liner. Hence it will not be possible to push it either upwards or downwards and this is the most critical condition we can reach to. Hence it is necessary to grind it before attempting removal of piston.

Q.704 If the piston ring gap remains insufficient when installing new rings, you should Ans. file the ends of the rings.Ends of the rings are to filed to have a proper butt clearance if required. As far as possible this should not be done because it may damage the profile of the piston rings or it may cause the excessive weardown of the liner or vertical scratching of the liner may take place because of the alteration of the profile of the piston ring. Hence as far as possible when new rings are to fitted the original methods must be utilized where the end gap clearance is always maintained.

Q.705 When inspecting piston rings through the ports of two stroke diesel engines black areas on the sealing surface are Ans. result of blowpast

Black areas are because of the blowpast where the lubricating oil get washed away. Due to blowpast and heat and the carbon deposit this particular portion of the ring as well as liner wall there will be a new patch of black surface. If this is happening, cylinder lubricating oil has to be increased or checked whether the piston rings are free in the grooves.

Q.706 An examination of the piston compression rings of an efficiently operated diesel engine should appear with a Ans. (a) shiny face end bottom and black end at the top.If the engine is efficiently operated when the piston rings are in very good condition, then the sliding surface of the piston rings over the liner should be shining without any black markings or scratching. At the same time the piston ring is rubbing at the bottom end of the groove so that the bottom end of the groove should also be shinning. As the gas goes behind the piston rings into the backside some carbon get deposited on the top and hence the top end of the piston ring may become black.

Q.707 Excessive side clearance between the side and the groove will causeAns. the ring to hammer the piston land below the ring.Excessive groove clearance will cause the ring to hammer on the piston ring groove bottom surface. This will especially happen when the piston is changing its direction, i.e. when the piston is at TDC and BDC, and the piston ring may break due to this. At the same time, the piston ring groove will wear faster.

Q.708 In certain cases the cylinder liner can be refinished rather than replaced when the properly honned Ans. liner surface should have a crosshatched pattern. When the liner surface have excessive scuffing or polishing effect and is not possible to retain the lubricating oil film on the liner surface then in that case it is necessary artificially to make it roughened out under the controlled condition. This is done by honing which is a method of cross pattern which will have the roughening carried out in two direction so that there will be tiny cavities on the liner surface which will retain the lubricating oil on the liner surface thus reducing the liner and the ring wear.

Q.709 One method of determining crankshaft misalignment is by Ans. (d) taking micrometer readings between the crank webs opposite the crank pin every 90 degrees or the crank angle rotation.This means that we are actually measuring the distance between the two crank webs at every 90 degrees position of the crank. The distance between the webs will change according to the misalignment of the crankshaft centerline. If the crankshaft centerline is misaligned because of weardown of the main bearings, the gap between the webs may increase at particular crank position and it may decrease excessively at particular crank position. Hence by comparing the web reading between these two positions, it is possible to find out the misalignment of the crankshaft.

Q.710 Which of the following statements concerning the cylinder liner wear in a single acting diesel engine is correct?

Ans. (c) Excessive liner wear causes wear between the piston rings and the groove.Excessive liner wear will cause the radial movement of the piston rings inorder to maintain the contact between the liner wall and piston ring surface. This continuous radial movement of the piston ring over the entire stroke of the piston will cause the piston ring to slide on the bottom of the piston groove. Hence there will be excessive weardown of the piston ring groove as well as the piston ring landing surface if the liner wornout is excessive.

Q.711 On large slow speed main propulsion diesel engine lower main bearing wear is usually measured by using Ans. bridge gauge.Considering that the crankshaft is sufficiently flexible and heavy enough, it will always keep the contact with the bottom half of the main bearing. If the bottom half main bearing wears down, the centerline of the crankshaft moves downward inorder to keep the contact with the bearing. Hence automatically the bridge gauge reading which measures the position of the crankshaft centerline with the fixed machine surface transverse girder. If this increases it indicates that weardown has taken place. This reading has to be compared with the previous reading so as to measure the weardown of the main bearing bottom half.

Q.712 The rate of wear on a cylinder liner depends on the (a) quality of air filtration. (b) effectiveness of lubrication.(c) type of fuel used.(d) All of the above.Ans. (d) All of the above.If the air is not properly filtered, along with air, sand and hard particles from the air will be drawn into the cylinder liner which will give the abrasive wear. If the effectiveness of lubrication is not proper, i.e. the quantity of lubricating oil is less or the lubricating oil is not injected at proper time, the effectiveness of lubricating oil is reduced because of which friction will increase and more weardown will take place. If the fuel contains more amount of sulphur, the liner will weardown because of corrosive effect. If the fuel contains more amount of abrasive particles such as silica, alumina then it will cause the abrasive wear and if the fuel contains more amount of vanadium, sodium then it will cause excessive amount of weardown because of hot corrosion.

Q.713 Abnormal crankpin bearing and piston skirt surface wear indicatesAns. incorrect connecting rod alignment.The connecting rod is to be aligned perfectly with the center of the liner and piston. If this alignment is not carried out properly, the centerline of the piston with respect to the liner will get altered. Under such circumstances, the piston will start rubbing against the liner wall thus giving excessive weardown of piston skirt. At the same time, it will cause alteration in the lubricating oil film produced in the bottom end bearing and hence bottom end bearing weardown will be non-uniform and excessive.

Q.714 To determine the main bearing clearances in a diesel engine, you should use

Ans. (c) plastic gauge.Plastic gauges are like lead wire in the form of stripes. These stripes are to flexed between the top half of the main bearing and the journal and the main bearing is to be tightened. When this is done the plastic will flow and the thickness of the plastic will get reduced and the width of the plastic will increase. This increase in the width of plastic is directly calibrated with the clearance in the bearing and hence the bearing clearance can be checked with the help of plastic gauges. These are more accurate and safe than any other method of checking.

Q.715 The ring land on a large low speed main propulsion diesel engine piston may crack due to Ans. insufficient ring groove clearance. If the ring groove clearance is insufficient in that case the ring will expand and get jammed up into the ring groove. As there is no further expansion possible it will exert excessive pressure over the land of the piston ring groove and because of this the stress concentration on the piston ring groove will exceed and cracks will originate on piston ring groove.

Q.718 A condition contributing to diesel engine piston ring sticking into the ring grooves is Ans. insufficient ring clearance at the ring sides i.e. the groove clearance.If the groove clearance is insufficient, the piston ring will expand because of heat and it will occupy the complete clearance which is available. As there is no clearance left, it will get jammed up in the piston ring grooves and hence it will get seized up in the piston ring grooves.

Q.719 Low compression in diesel engines could be caused by Ans. (c) worn or broken piston rings.When the piston rings are worn out or broken the sealing effect of rings with liner will get affected considerably. Hence during compression compressed air will get leaked out past the piston ring and it will blowback into the crank space or under scavenge space. This will result in loss of compression pressure.

Q.722 Which of the listed problems can be caused by low compression pressure in diesel engine?Ans. Combustion will not be proper.Actually due to low compression pressure, combustion will not be proper and when combustion is not proper there is a possibility that more carbon will be formed on the exhaust valve. The exhaust valve may start leaking, black smoke and turbocharger may get fouled and because of that the scavenge pressure may drop. All this things may happen because of the low compression pressure.

Q.723 Low compression pressure in a diesel engine may be a result of Ans. (b) excessive mechanical clearance between the piston crown and the cylinder head.When the clearance between the piston crown and cylinder head increases the clearance volume increases. Automatically the compression pressure at the end of stroke reduces

due of which the temperature and pressure of air will reduce which will cause improper combustion of fuel and may cause afterburning and high exhaust temperature.

Q.724 When a nozzle tester is used to check the spray pattern of an injector nozzle Ans. (d) the oil spray could cause blood poisoning if the spray penetrates the skin of the operator.It is well-known fact that with the high-pressure injection of the fuel, the fuel in highly atomized condition will penetrate the skin and the diesel will go into the blood and it will cause the blood poisoning. Hence during checking of a fuel injector valve on a test bed, it is not advisable to put your palm under the nozzle.

Q.725 When the piston is removed from a diesel engine for maintenance the piston should be examined for Ans. scouring, crack, burned spots, gummy deposits and sticky rings.The piston should be checked for whether the rings are free. If the rings are free then the ring grooves should be checked for formation of carbon and ash. At the same time, the piston rings and the landing site of the piston rings should be checked for cracks and any gummy deposits which are there on the piston rings and the grooves. This all will indicate if the lubrication is proper and quantity and quality of the oil is in good indication.

Q.726 To reduce the load during jacking operations which of the listed device should be operated?Ans. Indicator valve or cylinder test valve.During jacking operations i.e. turning the engine with turning gear it is necessary to open the indicator valve.

Q.727 After removing the old set of rings which of the following conditions is indicated if a bright spot is found on each end of broken rings?Ans. Butt clearance was not sufficient.If broken piston rings are to be examined and the broken ends are found out to be polished and shining, it indicates that the butt clearance was not sufficient. The main cause of piston ring breakage is the lack of butt clearance. Once the crack takes place, some amount of material will get removed and the clearance will automatically come into existence. This will cause the two ends of the rings to move over each other and hence the broken ends will get polished and automatically it will become shining.

Q.728 After an engine has been started using a * drive unit the drive gear or pinion disengage from the flywheel due toAns. the high rotational speed of the flywheel. In the * drive when the engine starts because of high speed of the flywheel, the pinion speed becomes excessively high. As a result, the disengagement of the pinion from the flywheel takes place and which avoids the damage caused to the pinion.

Q.729 Bearing crush as applied to diesel engine main bearing will result inAns. (a) positive sitting of the bearing in the housing.

Due to the crush there is interference fit between the housing and the bearing. The back side of the bearing will have frictional contact or interference contact or interference fit with the housing which will prevent the rotation of the bearing in the housing when the shaft is rotating. Thus it will give positive sitting of the bearing in the housing.

Q.730 Crank web deflection readings will give a positive indication of Ans. (a) worn main bearing journal. Whether the main bearing journal is worn out or the main bearing itself is wornout because of the wear down, the shaft will deflect downwards to maintain the contact with the bearing surface. Due to this the centerline of crankshaft will get sagged. Hence where the deflection is taken it will indicate an excessive crankshaft deflection. This will indicate that the bearing or the journal is wornout or the bearing housing has sagged because of the transverse girder of bedplate is sagged or distorted.

Q.731 When accumulated carbon at the air inlet port of two-stroke cycle diesel engine is removed you should take care Ans. to avoid carbon entering the cylinder.If carbon enters the cylinder, it may get lodged between the piston and the cylinder and cause the sticking of the piston rings. Ultimately it will cause the breaking of the piston ring and blowpast. Hence it is necessary that carbon should not enter the cylinder especially between the cylinder and the piston.

Q.732 Replacement piping for the diesel engine high pressure fuel system must be of same length and diameter as the original piping to Ans. avoid excessive amount of ignition delay.

Q.733 The burnt exhaust gas valve may be burnt by Ans. higher than normal exhaust gas temperature from a particular cylinder.If the exhaust valve is burnt out, the high temperature and pressure gases may leak past between the valve and the seat and which will ultimately give rise to the temperature of the exhaust gas after the valve. At the same time, the exhaust valve will start burning and hence there will be continuous rise in the exhaust gas temperature. Also there will be drop in the compression pressure which will cause afterburning and high exhaust temperature.

Q.734 In diesel engine a leaky exhaust valve can cause Ans. misfiring.Leaky exhaust valve will give rise to the drop in the compression pressure which will result in decrease in compression temperature due to which fuel may not ignite and which will cause misfiring of the fuel.

Q.735 The most severe cavitation corrosion occurring on the water side of a diesel engine wet cylinder liner normally occursAns. (d) near the middle of the thrust side of the liner.Thrust side of the liner is the side which has got the maximum thrust because thrust side of the liner, in case of two stroke engine, is on both side of the thrust side. In case of four

stroke engine, the thrust is taken by the liner depending upon the rotation one side will be thrust side which has got excessive amount of thrust transmitted to the liner wall by the piston skirt. This excessive thrust will cause the variation of the pressure and because of the variation of the pressure, the water pressure will fluctuate and because of fluctuation of water pressure, bubbling will start. At high temperature, bubble formation will take place which will cause the cavitation.

Q.736 Exhaust valve grooving and corrosion is caused by certain component of the residual fuel oil. These components are Ans. sodium, sulphur and vanadium.Vanadium, in presence of sodium, will give the hot corrosion because in presence of sodium, vanadium pentoxide which is formed because of burning of the vanadium will melt at much lower temperature in the range of about 500C. This molten vanadium pentoxide is highly corrosive and it will give the corrosive effect. Hence the combination of sodium and vanadium in the ratio of 1:3 is the most dangerous combination which will cause the grooving. Both sodium and vanadium are present in the residual fuel.

Q.737 Which of the listed cylinder liner surface condition indicates proper lubrication?Ans. Bright appearance.The liner surface should be dull white without excessive brightness or black spots or bright spots. Black spots indicate the blowpast and excessive bright spots indicates scuffing. Hence well runned and properly lubricated liner will have a dull silvery finish on the liner surface.

Q.738 Well lubricated bearing surface always appears Ans. dull white.Dull white is the colour of the overlay of tin which the topmost layer of bearing surface. Below this is the layer of nickle barrier which is hard and shining layer. Hence if the bearing is properly running and there is no wiping then the bearing surface must be dull silvery white.

Q.741 You are inspecting a lower main precision bearing on a diesel engine You observe that about half the thin babbit lining are of milky white color The condition is caused byAns. wiping out.If wiping out takes place, the top layer of tin i.e. overlay is wiped out. When overlay is wiped out there is bright nickel barrier will be seen as shiny spots. Hence half the babbit is already visible in a milky white color which indicates that wiping has taken place because of lack of lubrication or lubricating oil having water content or excessive loading of the bearing.

Q.742 You are testing a non-popping closed fuel injector diesel nozzle using a nozzle tester. A pressure less than the designed valve opening pressure is applied. If no fuel appear in the spray tip this indicatesAns. the needle valve is sitting properly and is not leaking.

The needle valve must only allow the fuel to inject when the injection pressure is reached and not below it. If the pressure is raised to less than injection pressure and if there is no leakage, it means that the injector is in very good condition and it is leak proof.

Q.743 Because of closed tolerance used in diesel engines fuel oil pump a worn plunger requires Ans. (b) replacement of pump plunger and barrel.The plunger and barrel are lapped to form a best sealing surface between them and hence it manufactured and lapped as a pair and it should be replaced as a pair. Replacing a single unit will cause excessive leakage or may cause seizure of plunger in the barrel. Hence it should be avoided and complete unit should be replaced, i.e. both plunger and barrel, should be replaced.

Q.744 Which of fuel nozzle listed requires the least maintenance?Ans. Pintle type nozzle.Pintle type nozzle will have a center hole and the hole is comparatively bigger one and it is completely covered by the pin at the tip of the needle. The needle sits squarely on the pin and hence there is less possibility of any distortion taking place between the needle seat and the valve seat and hence least amount of maintenance is required.

Q.745 When inspecting pistons, liner and rings of a large two-stroke diesel engine through cylinder ports a wet piston crown could indicate Ans. (a) leaky fuel injector.If the oil is accumulated on the top of the piston crown there is no other way that the oil can come on top of the piston other than a leaky fuel injector. When engine is in stopped condition, because of leaky fuel injector, the oil is accumulated on top of the piston. Under such circumstances, immediate action of replacing the fuel injector is most appreciated.

Q.746 Which of the listed devices could be used as a substitute for a ring grooving tools used to remove hard carbon deposits from the groove in preparation for installing new rings?Ans. (a) Section of removed compression ring.A section of a removed compression ring can be wrapped all around by a thin Emery paper and the ring section to be moved in the groove so that all around cleaning of the groove can be possible with the help of Emery paper which is wrapped around the section of the compression ring just removed.

Q.747 If the plunger or barrel of a fuel injection jerk pump becomes damaged Ans. The pump and barrel of the pump must be replaced as a unit.

Q.748 Surface irregularities such as erosion and pitting on the injection pump plunger will Ans. effect the fuel oil metering.If there is excessive erosion or pitting on the plunger then the integrity of the sealing between the plunger and barrel will be affected. As a result, the high-pressure oil will

leak past the plunger. Hence the quantity of oil injected into the engine will reduce and which will affect the metering of fuel to the engine.

Q.749 Side clearance (groove clearance) of the compression rings on a diesel engine piston is necessary to Ans. for the gas to have easy access to the back of the piston rings.Due to the easy access, it will force the piston rings against the liner walls. Hence this clearance is very important. If this clearance is less or the space between the ring and groove gets clogged or deposited with carbon, sufficient amount of gas will not find its way behind the piston rings. Hence the contact pressure between the piston rings and liner will reduce which will cause the blowpast and weardown of liner and breakage of liner and piston rings.

Q.750 If lost motion is present in a individual fuel injection pump which of the following problem will occur?Ans. The fuel injection will occur late.Due to the lost motion, the exact motion of cam will not be transferred to the plunger movement and hence there will be late injection because the position of plunger with respect to the cam will be retarded.

Q.751 In a large low speed propulsion diesel engine if the injectors have formed carbon around the nozzle holes which of the following would help avoid further building up?Ans. Decrease the injection cooling water temperature.This may be happening because of the excessively hot fuel injector nozzle due to which the sealing between the nozzle and the seat is affected and nozzle will start leaking. If the nozzle starts leaking, formation of carbon deposit takes place.

Q.752 A condition contributing to diesel engine piston ring sticking in the ring grooves is Ans. insufficient ring clearance at the ring gap or side clearance.If the groove clearance of the piston ring i.e. axial clearance between the piston rings and the ring groove if it is less then in that case the piston ring will expand. At the same time some carbon deposit may take place between the groove and the piston ring will cause the piston ring to get seized or stick up in the groove. Hence sufficient clearance has to be maintained between the groove and the ring.

Q.753 In diesel engine when installing new piston rings it is important to check (a) ring gap clearance.(b) side clearance .Ans. Both (a) and (b).It is necessary to check both the butt clearance and groove clearance. If any of the clearance is less, it will cause the breaking of the piston ring or seizing of the piston in the groove which will ultimately cause the malfunctioning or improper combustion of the fuel and which may cause liner breakage, scuffing, piston ring breakage or loss of power.

Q.754 The purpose of interference angle in a diesel engine exhaust valve is to (a) work in conjunction with valve to rotate the valve.(b) break up the seat deposits.Ans. (b) break up the seat deposits.Actually interference angle of about ½ degree is given between the seat and the valve so that when the actual operating temperature reached it will expand. It will have a proper contact with the seat. At the same time, when this action is taking place, any carbon deposition that is present between the seat and valve will get crushed and removed. Hence it acts like a self cleaning method of the seat.

Q.755 When accumulated carbon at air inlet port of a two stroke diesel engine is being removed you should take care to avoid carbon particles Ans. entering the cylinder.(ALREADY DISCUSSED)

Q.756 You are installing new piston rings on a single acting diesel engine piston. To check the ring gap clearance, the ring should be placed Ans. at the point of minimum cylinder wear.At the point of minimum cylinder wear you will have the minimum gap clearance which will be your yardstick for the proper operation of the engine. If the clearance is satisfactory at the position of minimum weardown then it can be surely assured that when the piston is at top position where the weardown of the liner is maximum there will be sufficient clearance between the ends of the piston. Hence during entire stroke of piston there will not be a single position where the piston ring ends will butt against each other and cause cracking of the piston rings, seizure of the piston ring or cracking of the liner. Hence as a safety measure, butt clearance is always measured where there is minimum weardown.

Q.757 A defective injector nozzle in a propulsion diesel engine can cause(a) engine power loss.(b) smoking due to unburnt fuel.(c) high exhaust temperature reading.(d) All of the above.Ans. (d) All of the above.If the fuel injector nozzle is defective i.e. it is not spraying properly or if it is not penetrating properly or if the nozzle is leaking or if the holes are choked, the fuel will not be atomized properly and penetrated which will result in improper combustion. Because of improper combustion, there will be loss of power, afterburnining, and hence unburnt fuel and smoke in the exhaust and the exhaust temperature will rise.

Q.758 Which of the following problems is the main source of fuel pump and injection system malfunctioning?Ans. Improper adjustment.Improper timing adjustment of fuel pump will ultimately lead to improper functioning of the fuel injector and fuel pump which will ultimately lead to loss of power, excessive weardown of the piston rings, black smoke, excessive carbon deposits, turbocharger

surging. All these problems will be because of improper adjustment of the fuel pump which will ultimately cause the improper adjustment or improper spraying of nozzle holes.

Q.760 If you have determined that entrained air in fuel nozzle system is causing a diesel engine to stall you should first check forAns. a loose fitting in the booster fuel pump suction piping.If there is loose fitting on the fuel booster suction piping, the fuel booster pump will draw the air. This air will cause the problem of air traps in the fuel injection system because booster pump suction side is the only low pressure side in the entire fuel injection system and hence possibility of air leakage is more.

Q.761 In a large low speed diesel engine excessive piston clearance can be restored by Ans. inserting shims between crankpin bearing box and connecting rod foot.By inserting shims between the bearing box and connecting rod foot the piston position can be raised in the liner. When the piston position is raised in the liner automatically the clearance volume reduces and the compression pressure increases. It can be restored back to the original.

Q.762 Which of the following procedures should be carried out to permit the use of crosshead engines with an inoperable aftercooler?Ans. Run the engine at reduced speed until the cooler can be repaired or renewed If the cooler is not working then the temperature of the air which is admitted to the engine will be very high. When the admitted air is high the density reduces and hence the quantity of air admitted will be less and the quantity of fuel that can be burnt will have to be reduced. At the same time, as the air temperature increases the exhaust temperature will also increases. Hence complete thermal loading of the engine will take place and at the same time because of higher temperature in the cylinder lubrication will also get affected. Hence in order to avoid all these things it is better to run the engine at lower load.

Q.763 A faulty injector in one cylinder of an operating diesel engine can be located by Ans. (a) cutting out the individual injector and noting the engine performance.Faulty injector in general can be detected by exhaust temperature of the unit but it is not a reliable method. Hence one has to take the draw card. By draw card you can find out the compression pressure and peak pressure. If the compression pressure is satisfactory and peak pressure is varying, it clearly indicates that the injector is bad.

Q.764 Which of the following conditions will cause carbon deposit to form in the piston ring belt of a diesel engine?Carbon deposit on the piston ring belt can be caused because of faulty combustion, excessive ring temperature or over lubrication. All this will lead to carbon formation. If the combustion is not proper, more amount of carbon deposits will be formed on the piston rings. If excessive lubrication is given the excess oil will get burnt, it will form

carbon and ash and they will also lead to carbon deposits on the piston ring. Also if the ring temperature is excessively high i.e. the cooling of the piston is not properly done in that case the lubricating will burn which will form carbon deposits on the piston rings.

Q.767 A change in the degree of fuel atomization will affectAns. (b) fuel penetration.Penetration and atomization both depends on the hole size of the nozzle as well as the injection pressure. But as they are opposite to each other if excessive penetration takes place which occurs because of the increase in diameter of the injection holes the atomization reduces. On the other hand, if the holes are of very small size which will cause more amount of atomization. In this case, because of the pressure drop during atomization, the penetration will reduce. Hence as they are opposite to each other as atomization increases penetration decreases and vice-versa.

Q.768 Which of the following problems may occur if the clearance between the piston and the cylinder is insufficient?Ans. Excessive wear, scuffing of the liner and piston seizure.There will be excessive wear of the liner as well as the piston as excessive pressure is developed by the rings over the liner walls. At the same time, the skirt of the piston will come in contact with the liner wall and wiping out of the lubrication oil will take place which will also cause excessive wear of the liner. At the same time, as the expanded piston will come in contact of the liner wall it will wipe out the lubricating oil film. When the lubricating film is wiped out because of metal-to-metal contact between the piston and liner wall there will be scuffing of the liner and blowpast. If the clearance is excessively low and the piston expands beyond that clearance, the piston will get seized in the liner.

Q.769 Black areas on the sealing surface of the piston rings indicatesAns. passage of hot gases or blowpast.Black areas is an indication of blowpast and the lubricating oil is wiped out between the ring and liner and the areas get coated with carbon deposits from the exhaust gas or high pressure gas.

Q.770 A bright side on the compression ring of a diesel engine indicatesAns. properly functioning of the rings.The job of the rings is to seal the surface between the liner and piston against the high pressure and high temperature gases. When the piston and the liner surfaces are rubbing against each other it will give a polishing effect as long as there is no blowpast and the surface remains polished. This indicates that the sealing between the piston rings and the liner is proper and the piston rings are functioning properly and the cylinder lubrication is also proper to maintain the seal between the liner and piston rings.

Q.771 The best tool to remove the carbon ridge at the top of engine cylinder prior to removing the piston is to useAns. metal scrapper.

Metal scrapper is used to remove to ridge formed because of carbon. If the ridge is formed because of the weardown of liner and it is a metal ridge, it is to be removed by use of hand grinder as it cannot be removed by metal scrapper.

Q.772 Which of the following devices is commonly used to measure the clearance between the main engine bearing and crankshaft?Ans. (a) Plastic gauge.Plastic gauge are utilized like lead wire and they are made to compress between the bearing and the journal and because of the compression the thickness will reduce and the width will be increase and the increase in width can be directly calibrated in terms of clearance.

Q.773 Which of the following condition can result in cracking of the piston land?Ans. Insufficient ring groove clearance.If the ring groove clearance is insufficient, the ring will expand and it will occupy the complete space in the ring groove. Further expansion of the ring in the groove will cause excessive stresses induced on the piston ring groove which will cause cracking of piston land.

Q.774 Which of the following conditions may occur while using fuel with high sulphur content?Ans. (d) CorrosionIf fuel with high sulphur content is used, sulphur will burn and it will convert into sulphur trioxide and in presence of water and moisture it will convert into sulphuric acid which is highly corrosive. This will give the corrosive wear on the liner.

Q.775 If the back clearance of a piston ring is excessive There will be excessive amount of carbon deposits behind the piston rings and there will not be enough support for the piston rings. Under such circumstances the piston rings will protrude more from the ring groove and it will cause the piston ring to collapse or twist and break.

Q.776 Which of the following conditions could contribute to the cracking of diesel engine cylinder head?Ans. Blocked cooling water passages to the head.If the cooling water passages to the head are blocked or scale formation takes place in the cooling water spaces, the cooling of the cylinder head is reduced and it is subjected to very high temperature and pressure. Because of this high temperature and pressure, in order to maintain the strength of the cylinder head, it is necessary to cool the cylinder head and maintain the temperature of cylinder head. If the cooling is not carried properly, the strength of cylinder head will reduce which will ultimately cause the cracking of the cylinder head.

Q.777 A properly honed diesel engine cylinder liner will Ans. shorten the breaking in period.

A cross honing is carried out so as to give controlled roughness on the cylinder liner surface. At the same time to have the retention capacity of the lubricating oil on the cylinder head surface. Both of this will contribute to the faster running and faster breaking in period so as to prevent scuffing or blowpast. Hence honing is done at the initial stages on new liner or if the liner is excessively glazed and the surface is too smooth to retain the lubricating oil.

Q.778 A scoured diesel engine cylinder liner will causeAns. rapid wear of the piston rings.If excessive scouring is present on the cylinder liner blowpast will take place. When blowpast takes place the lubricating oil film between the liner and piston will get distorted and there will be excessive metal-to-metal friction between the liner and the piston rings due to which excessive weardown of the piston ring will take place.

Q.779 Which of the following operating conditions can occur when shims are removed from the joint between marine type diesel engine gearing box and the foot of connecting rod?Ans. The piston position will move downwards with respect to the cylinder head.When the shims are removed, the piston will move downwards with respect to the cylinder head. Hence the compression pressure and clearance volume will increase and compression ratio will reduce.

Q.780 After long period of operation a wear ridge caused by piston ring action will developed near the top of the cylinder liner This ridge must be removed when piston rings are removed inorder to Ans. prevent breaking of the top ring and land or both.If the ridge is not removed while removing the piston it may happen that the rings may get jammed up in the ridge and it may cause the seizure of the piston in the liner. When new rings are fitted and the piston is lowered and the ridge is not removed, the piston rings will hammer against the ridge which will cause the breaking of the piston rings and damage the landing face of the piston ring groove. Q.781 Crank lead can be adjusted to change which of the listed operating conditions?Ans. Longer combustion event.When the crank lead is adjusted the injection timing gets adjusted. When the injection timing gets adjusted, the combustion can be delayed or advanced.

Q.782 When hydraulic valve lifter is on the base circle of the cam, zero tappet clearance is maintained byAns. plunger spring. When the hydraulic valve lifter is on the base circle the plunger springs will lift it against the base circle and hence the tappet clearance is maintained. During this time, due to the spring action on the valve plunger, the plunger will be pushed downwards and the roller will keep contact with the base circle of the cam. Hence zero tappet clearance will be maintained.

Q.783 In a diesel engine blowby is generally a result of Ans. worn compression ring.Blowby or blowpast is because of improper sealing between the cylinder liner walls and the piston rings. This is because of the excessive weardown of the liner wall and piston rings or improper or uneven weardown of liner wall and piston rings so that the sealing gets affected and blowpast will take place.

Q.784 Which of the listed condition can cause lacquer to be deposited on the piston skirt?Ans. High lubricating oil temperature.Because of high lubricating oil temperature, the lubricating oil will burn over the piston skirt. When the lubricating oil burns a lacquer like formation will take place and deposition will take place on the skirt.

Q.785 Scuffed diesel engine cylinder liner wearing surface in a diesel engine can result from Ans. applying load to cold diesel engine.When the engine is cold it will take some time to form a good sealing between the piston rings and the liner. Hence the load should be kept low initially and increased gradually. If the load is suddenly increased, blowpast will take place between the piston ring and the cylinder liner wall. When blowpast takes place it will wipe out the lubricating oil between the liner and piston ring and which will cause the excessive friction between the liner and piston ring which will ultimately cause excessive scuffing of the liner.

Q.786 If a diesel engine driving a generator turns over freely but fails to fire properly, the cause could be Ans. air in the fuel.If the engine can accelerate sufficiently to the firing speed and the fuel is released by the governor but the engine does not pick up on fuel, this indicates that the fuel is of bad quality and one of the reason is that the fuel contains air or water.

Q.787 When diesel engine compression pressure is checked Ans. the indicator cork is kept open.When the indicator cork is connected to the cylinder head, the indicator cork is kept open so whatever the change of pressure is taking place inside the cylinder at different positions or movements of the crank or the main piston will be directly indicated by the stylus movement of the indicator piston.

Q.788 In a diesel engine exhaust system the cooling of the exhaust gases below their dew point will result in Ans. sulphuric acid corrosion.If the fuel contains sulphur it will form sulphuric acid and if this sulphuric acid is in the form of vapour but if this vapours are allowed to cool below the dew point then it will convert into liquid form and it will cause excessive corrosion of the liner.

Q.789 Which of the following statements is true regarding the installation of piston rings on two-stroke diesel engine as compared to four stroke diesel engines?Ans. Some provisions must be made in two stroke diesel engines to prevent the rings from bending in the ports.In two-stroke engines, there will be ports in the liner walls over which the piston rings will slide. Hence it is necessary to make sure that the ends of the piston rings will not get entangled with the ports and the piston rings will not break. In order to avoid such things the ends of the piston rings, in two-stroke engines, are slightly curved inside so that during the operating temperature they will not get entangled with the ports and get broken.

Q.790 In a large low speed diesel engine the clearance between the piston crown and cylinder head is found to be excessive. Inorder to correct this Ans. shims should be inserted between the crankpin bearing box and connecting rod foot.In case of marine type of connecting rod, where connecting rod is fitted on top of bottom end bearing, it is possible to insert the shims between the crankpin bearing box and connecting rod foot so that the position of the piston in the cylinder liner with respect to the cylinder head can be altered. Hence the compression pressure and clearance volume can be changed.

Q.791 Bouncing of valve gear in a diesel engine can be caused by Ans. spring surge.If the spring is not getting released or if it is not following the action of rockerarm when the rockerarm moves upward, the spring will not push the valve upward. After sometime, it will cause the valve to push upwards in the gap between the valve and rockerarm. During this time, the movement of the spring will be abrupt due the stored compressed energy in the spring and this will cause the surging effect of the spring and the valve. This will cause the valve and the spring to get damaged. This can also be caused because of sticky valve in the guide.