Jimei university Operating troubles and their remedies Lesson 11

Jimei university Troubles may occur when the engine is running. If the engine does not start on air, it may be due to one or more of the following causes:

Jimei university starting air pressure (2.5— 3.0MPa) too low, incorrect timing of starting air valves, one or more of the starting valves or distributor valves stuck in closed position,

Jimei university master valve not actuated, stop valve on air line is closed, or if starting after working on the engine, the turning gear still engaged.

Jimei university If the engine turns too slowly or irregularly on starting air, the possible causes may be

Jimei university the pistons in starting air distributor sticking, starting valves in cylinder covers defective, faulty timing of the distributor.

Jimei university The starting air pressure too low may also be another cause. If the engine does start on air, but combustion does not immediately begin,

Jimei university the cause may be low compression, failure of the fuel pumps to discharge oil into the fuel valves or incorrect timing of fuel pumps.

Jimei university Failure of fuel injection is usually due to the troubles in the fuel injection pumps.

Jimei university *However, the injection may be delayed, though the pumps are in good order, if the fuel lines to the injection valves have not been cleared of air.

Jimei university If there is no fuel injected into the cylinders, the possible causes are fuel gasification( 汽化 ) due to excess temperature, pressure before fuel injection pumps too low, fuel too cold, except the troubles in the injection pumps.

Jimei university *Sluggish( 行动迟缓的 ) movement of maneuvring gear, incorrect adjustment of maneuvring gear, shut-down devices on engine having operated, maneuvring air pressure to governor too low, failure in governor may be the case also.

Jimei university These can be indicated by too low fuel pump index( 刻度盘上的 刻度 ).

Jimei university If the action of the engine indicates that some of the cylinders are not firing, the ones affected may be determined by watch the exhaust temperature.

Jimei university A common trouble with the fuel pump plungers or fuel valve spindles is oil leakage.

Jimei university Good strainers and filters should be provided in the fuel oil system and they should be cleaned at intervals, so as to prevent dirt from getting under a fuel injection pump valve and causing it to leak.

Jimei university *It is not uncommon for the lubricating oil pump suction to be clogged with the dirt left in the crankcase after work has been done on the engine.

Jimei university Excessive clearances in the main or crankpin bearings will sometimes be indicated by loss of pressure in the lubricating system before any bearing knock is heard.

Jimei university The engine may lose power or slow down when running. When this occurs, the first cause possible may be hot bearings and seizures of the pistons in the cylinders.

Jimei university Failure of the fuel supply to one or more cylinders may be another cause.

Jimei university Cracks in the cylinders and cylinder covers may result from unequal heating. The cylinder covers should be regularly vented by opening the vent cocks.

Jimei university *Cracks usually resulting from local overloading are caused by troubles with the fuel pumps or one or more cylinders not firing.

Jimei university If indicator diagrams are taken at regular intervals, any unequal distribution of load will be easily found out.

Jimei university Bearing knocks are likely to occur from bearing wear. Valve gear knocks are more easily located while the engine is running.

Jimei university Knocking that occurs between cams and rollers may be caused by troubles such as excessive clearances and worn or broken rollers, or the trouble may be in the valves.

Jimei university *Blow-off( 喷出、放气 ) of the relief valves of the main cylinders during operation indicates that the cams are not properly set, if the blowing-off is not due to leakages or slackening( 松弛 ) of the springs.

Jimei university *In such case the cylinder affected should be immediately cut-off and the cause of the trouble traced( 查找、寻迹 ) by taking indicator diagrams.

Jimei university *Most troubles likely to occur with marine diesel engine can, if located in time, be remedied with no difficulty, and many can be avoided if

Jimei university if the engine is maintained with a high sense of responsibility to the people on the part of the motormen and engineers.

Jimei university Reading Material Trouble shooting( 故障诊断 ) Faults will develop in prime movers of any type or make.

Jimei university Burmeister & Wain engines are very reliable but they very wisely provide excellent documentation to cover many contingencies( 偶发 事故 ) which may only rarely, if ever( 如果有发生过的话 ), arise.

Jimei university This includes: Emergency slow-down and shut-down limits (shown on Table 1);Emergency slow-down and shut-down limits (shown on Table 1); Starting failures(see Table 2);Starting failures(see Table 2); Running defects (see Table 3).Running defects (see Table 3).

Jimei university Table 1—Emergency slow- down and shut-down limitsTable 1—Emergency slow- down and shut-down limits Table 2—Starting failuresTable 2—Starting failures Table 3—Running defectsTable 3—Running defects

Jimei university B. OPERATION WITH PISTONS AND CONNECTING RODS REMOVED

Jimei university If some cylinder unit components, such as piston, connecting rod or big end bearing are damaged and can't be repaired, the following can be done to make emergency operation possible.

Jimei university 1. Remove the piston, connecting rod and big end bearing of that unit. 2. Cover lubricating oil bore in crank pin.

Jimei university 3. Fit a completely assembled cylinder head without the valve push rods. 4. Disconnect the pilot air pipe to avoid starting air to the cylinder head.

Jimei university 5. Set the HP fuel pump out of service by blocking pin.

Jimei university *With one cylinder out of operation exhaust gas temperature of the remaining cylinders should not exceed normal full load temperatures.

Jimei university If the turbocharger(s) surges, reduce load further to avoid continuous surging.

Jimei university *Engine operation with a piston and connecting rod removed from one or more cylinders, should be performed only in absolute emergency when no other means are available.

Jimei university Removal of one or two counterweight(s) may induce( 导致, 引起 ) vibrations due to unbalance. Please contact Stork-Wartsila Diesel in such a case.

Jimei university When the engine should be operated with one cylinder out of service, the balance of the engine is disturbed( 扰乱的 ) and severe or even dangerous vibrations may occur.

Jimei university The vibration conditions are in practice depending on the type of the installation.

Jimei university C. INSPECTION OF CRANKSHAFT BEFORE IRON-PLATING( 镀铁 )

Jimei university Since most crankshafts are susceptible to( 容易受到 ) progressive fracture( 扩展裂 缝 ), either from repeated bending or from reversed torsional stresses( 扭转应力 ),

Jimei university and fatigue strength( 疲劳强度 ) is greatly dependent upon the surface and radius states of journals and crankpins,

Jimei university the first inspection before iron plating is to check if cracks exist on the worn surface or radius.

Jimei university Where appropriate, dye penetrants( 着色渗透 ), magna- flux( 磁粉探伤 ) and other testing methods can be used to check for cracks, but sometimes it is still difficult to measure accurately the depth of a crack.

Jimei university Therefore, in all cases, cracks must be completely ground down( 磨掉 ) before iron-plating.

Jimei university During prolonged( 延长的 ) periods of engine operation, off-centering( 偏心 ) of a crankshaft often takes place.

Jimei university Thus, it is necessary to check and correct the center line by the heating method before grinding and iron plating.

Jimei university While heating, special precautions must be taken to avoid creating thermo-cracks.

Jimei university After the heating process, grinding can be carried out, and it is necessary to avoid any springing( 弹性挠曲变形 ), and the original fillet( 内圆角 ) radius should be retained( 保持, 保留 ) for strength.

Jimei university According to the technical requirements from CCS and other societies, unless a crack still exists after a crankshaft is ground down to its minimum diameter limit,

Jimei university the crankshaft can be restored by the iron plating process.