AKRAMANUJAN.ORG30th OCTOBER 2019

FUNCTION 4(11)

ramanujan1933@gmail.com

NOTE:- i am once again repeating the request for questions from other centres so that it helps you all in preparing for the orals. you can send hand written scanned sheets of questions to my e-mail given at the head. Please treat this as urgent.

QUESTIONS FUNCTION 4

KOCHI

Mr Subramanian Jan 2015(11)Explain the Sulzer engine fuel pump setting and how

the lead is adjusted. Answer:- Before taking a check on fuel pump setting the following adjustment in engine control system is necessary. The telegraph lever, running direction safety interlock are to be set for the running direction in which the engine is turned. The oil pressure in the cross head line must be built up for the reversing servomotor to take up its correct end position. The wood word governor should be set for an admission position. The load indicator should take its position with respect to engine setting .

cut out check-The zero position of load indicator, cut out servomotor and the wood word governor must coincide and the position must correspond with no delivery of all the pumps.

For adjustment, the maker valve setting table should be consulted. The idle stroke (LH) of the plunger before commencement and the effective stroke (EH) should correspond with a given test result position of load indicator. The fuel pumps are delicately balanced for equal maximum pressure, power generation and exhaust temperature by trial at the maker’s test bed. The procedure just detailed may be adopted for a periodic check or for setting a replacement pump. All other possibilities to remedy a faulty condition should be taken into consideration before altering the length of push rod. When lengthening the push rod of the suction valve, the effective stroke will be shortened and the commencement of delivery will occur late. When lengthening the push rod of the spill valve the delivery will be terminated early.

(12)Explain how the thrust pads are examined and how the clearances for both ahead and astern side are checked.

Answer:-

To find the average oil clearance of the pads, this is done during the CSM of the thrust block. The oil is drained out of the thrust block. The top cover is opened and removed. If the engine has stopped on the astern last movement, then the ahead pads are accessible and the clearance of the ahead pads can be found out. Remove the ahead side carrier ring bracket held by two or three bolts. using a long wooden baton the pads can be pushed out one by one through the top opening. They can be cleaned individually and inserted in the pad carrier in the same way they came out. Using long feelers , the average clearance can be measured from both sides . This is recorded. The carrier ring stopper is fixed. Clean oil is filled in to the correct level and the top cover fitted back.

caCARRIER RING STOPPER

To check the astern pads, the engine may have to be turned on starting air for a few turns on the ahead direction to make the astern side clear and the procedure repeated for the astern pads check.(13)Describe the B&W engine chain tightening procedure..Are the fuel pump and exhaust valve timings affected . If so how are they brought back to their original condition.

Answer:- (c)The chain stretch condition is normally checked every 4000 hours of working of the engine. The slackness is measured by measuring the sag on the slack side of the chain. It should be between half link length and one link length. The method of measuring the sag is shown in the sketch illustrated below.

The chain is tightened by slackening the checknuts of the jockey wheel and turning the jack screw to tighten the chain to the required tightness as stated above.When tightening the checknuts the spring compression should be checked and maintained to the same length as indicated by the length etched on the chain frame

(a) The effect of tightening the chain leads to a small shift of the camwheel, thereby altering the timing

slightly. This effect has to be corrected and that procedure is shown in the next sketch

The tolerance allowed in shift is within 2 degrees. This operation is repeated for the other half of the camshaft with the same reference of number one unit at TDC

(14)What are the advantages of roller bearings as compared to sleeve bearings.Answer:- Roller bearings work on the principle of rolling friction. As compared to sliding friction the coefficient of friction is less for rolling friction as compared to sliding friction for the same boundary lubrication condition. Hence roller bearings absorb less power than sliding bearings and this applies only to the same boundary lubrication condition. The same sliding friction condition is many more times improved in a sleeve bearing by introducing hydro dynamic lubrication whereby a hydrodynamic fluid film sustains the load and so power wasted in friction is considerably reduced. this system will only work when speeds of rotation are high and the sleeve bearing material is White metal whose

coefficient of friction is very low. Hence the B&W T/C whose speed is in the range of 10000 RPM uses sleeve bearings WM lined, whereas the Brown Bowery VTR T/C uses roller bearings mounted on resilient leaf springs since the speed of the speed of this T/C IS 4000 RPM. Roller bearings are subjected to brinnelling whereby the roller races get pitted by impacting and that damages the bearings. For this reason the bearings are mounted on resilient springs.

(15)What is boundary lubrication . where is it commonly found on the ship.Answer:- Boundary lubrication is sliding friction where the oil or grease is smeared to reduce the coefficient of friction. There is surface to surface contact with the oiliness only to allow easy slippage. The most common example of boundary lubrication is the cylinder lubrication for the sliding movement in the liner. Other examples are the lubrication of the bearings of the deck machinery such as windlass and mooring winches, which are grease lubricated.

(16)Draw the T/C lub oil system line diagram. What is the purpose of the header tank.Answer- The header tank situated at about 6 meters above the T/C gives a constant head or pressure of oil, which ensures that the lubrication is optimum. . This will ensure that the oil pressure reaching the bearings should never fall below a pressure of 1.6 bar .If level of oil falls below the mouth of the inner drain pipe it is quickly emptied and an alarm condition initiated.. After an alarm it takes about ten minutes to empty the high level tank which is sufficient to ensure adequate lubrication of the

turbochargers as they run down after the engine is stopped.

(17)What is difference between Sulzer and B&W main bearing.Answer:- The B&W engine main bearing is the conventional type with holding studs and a top keep with the top shell and the keep is tightened by nuts on the studs and provided with locking devices. Whereas the Sulzer engine the keep is held in place and tightened by two jack bolts which rest against a landing on the A frame and the jack bolts press against the keep. The bolts are in compression , whereas the studs in the B&W engine are in tension. The change in design made by Sulzer is to bring the tie rods closer to the centreline so that the bending moment induced in the bed plate girder is reduced. (18)Why Sulzer engine main bearings are held by jack

bolts and how are they secured.

Answer:-

The above sketch shows the method of securing the main

bearing top keep by the two jack bolts which are in compression. The top of the bolt rests against the A frame stiffener and the bottom side of the bolt fits in a depression made on the keep to prevent the bolts from slipping out. This design is made to suit the minimal axial distance between the tie bolts so that the bending moments are reduced on the transverse girder.

December 2015 Mr subramaniam(19)How will you check the exhaust valve timings of the engine you have worked on.Answer:- The following safety precaution shall be taken.: Since the engine is to be turned a propeller clearance

will be obtained from the deck department until completion of the jobThe cam casing plates shall be opened to observe the cam roller and the cam

If we are going to find out say the exhaust timing of no 1 unit , find the TDC position for no 1 unit which will be marked on the fly wheel rim just above the degree markings.. Turn the engine in the ahead direction till the cam roller just makes contact with the cam profile. Note the angle on the fly wheel in degrees. This is the position of opening of the exhaust valve. Opening position of the exhaust in degerees after TDC = angular position of the cam as noted - the angular position of TDC as noted.---------opening position. Continue turning the engine in the ahead direction till the the cam profile is just leaving contact of the roller . This may be verified by a feeler gauge to be sure. Note the angular position on the fly wheel Closing position of the exhaust in degrees after TDC = angular position of tyhe cam as noted -- the angular position of TDC. The closing and opening positions are thus noted and should be verified with the manual.

(20)What is the reason for taking crank shaft web deflections.Answer:- When uneven wear takes place along a line of main bearings, the effect is to cause changes in the deflections measured between the crank webs. Any change in deflectionfrom the naturalcan be related to misalignment in the main bearings, as the change of deflection is proportional to the difference in height of the main bearings. The makers provide the deflection readings taken during sea trials which may be considered as the initial reading. The makers also recommend change of the lower half of the bearings when the readings exceed a limit. Hence a decision to change the worn bearing can be easily determined based on this assumption. This can be further confirmed by taking bridge gauge readings.. Deflection readings are therefore taken to ascertain

quickly whether the alignment is of the crankshaft is within reasonable limits or whether realignment is necessary.