Answer MEP Question 64
Q. A. As the second engineer describe the procedure involved in the complete inspection of a cylinder liner and piston assembly, indicating areas of significant interest.
B. Explain with reasons, possible faults which might be found;
C. Suggest how such faults might be avoided.
As 2nd Engineer describe the procedure involved in the complete inspection of a cylinder liner and piston assembly, indicating areas of significant interest.
A complete inspection will require all components to be removed from the engine and fully dismantled. The initial inspection should be carried out before the components are cleaned to monitor fouling rates, areas of concern such as very dirty liner walls.
Once the components have been cleaned, gauging and measurement can be carried out before the final inspection is done.
- When the piston has removed the cylinder, the surface should show worn-bright in appearance and oily. Black patches appearing on the liner surface indicate a leaky piston ring.
- A dry but 'mirror surface' indicate local failure of lubrication as a result of severe galling action. The surfaces were seized and eventually hardened.
- The formation of sharp edges along with the ports and ridge on the top extremity of the piston travel is observed and if exists, to be ground of smoothly.
- When a hard surface due to micro seizure appears on the surface it should be rubbed by a rough grind-stone.
- Any vertical scoring marks should be smoothened by polishing with an oil stone. The horizontal ridge mark should be ground off.
- Cylinder line wear is measured with an inside micrometre length gauge. A reference strip is prepared with holes at measure points that can be held against the liner surface.
- The gauge ensures that the measurements are taken at the same vertical position with respect to liner surface every time at each diametral position the readings are taken along the fore and aft and athwartships directions. The maximum value from these readings gives the wear in the liner.
- For a large bore supercharged engine the permissible liner wear is 0.6 to 0.7% of the original bore.
- For an engine of bore 760mm the maximum permissible wear is 5mm and an ovality of 1mm. For each cylinder, the result should be presented in the form of a graph showing the rate of liner wear with time.
- In engines burning residual fuel, with proper combustion and lubrication by an alkaline cylinder lubricating oil the rate of liner wear should be between 0.05 to O.lmm per 1000 working hours.
- For 4 stroke engines burning distillate fuel or blend with selected residue oil the rate of wear should be much lower, being within the range of 0.018 to 0.025mm per 1000 working hours.
Specific areas of inspection are,
1. Liner Wall
2. Coolant side of the liner.
3. Lubrication Quills.
4. Piston Crown
5. Coolant side of the piston,
6. Piston ring area.
7. Piston rod.
8. Piston Internals.
B. Explain with reasons possible faults which might be found.
i. Excess wear on liner: In-sufficient lube oil, abrasive in the fuel, Liner too cool
2. Cracks on the liner: Fuel impingement (Injection Fault or FO too cold)
3. Deposit on the liner coolant side: Treatment insufficient or oil in water
4. Lubricator quills: Poor or nil operation due or supply system defect
5. Burning and cracking of piston crown: Due to fuel impingement or insufficient coolant
6. Deposit on piston coolant side: FW treatment insufficient or LO depletion
7. Wear of piston rings and grooves: Insufficient L.O, abrasive in the fuel oil, poor combustion (Causes excessive carbon build-up)
8. Scoring of the piston rod: Heavy dirt in the scavenge space. Excess spring tension
9. Cracking of the piston mating surfaces: Caused by incorrect tensioning procedures
C. Suggest how such faults might be avoided.
* Ensure adequate LO supply, clean fuel using separator at low throughputs, operate FW coolant at 80 deg C.
* Regular inspection and testing of the fuel injector, the correct setting of FO viscosity control to 12 cst.
* Weekly checks of FW condition for nitrate measure and low level of chlorides:
* Regular check of flow rate from cylinder LO unit, plus daily consumption.
* Check piston coolant flow alarms,
* Use LO analysis to ensure LO condition maintained correctly.
* Regular checks of combustion efficiency by maintaining the fuel injection equipment properly,
* Regular cleaning of scavenging space and monitor condition of stuffing bore drain.
* Check the intervals of the piston and correctly tenSion piston studs and apply the fastening device.
A complete inspection will require all components to be removed from the engine and fully dismantled. The initial inspection should be carried out before the components are cleaned to monitor fouling rates, areas of concern such as very dirty liner walls.
Once the components have been cleaned, gauging and measurement can be carried out before the final inspection is done.
- When the piston has removed the cylinder, the surface should show worn-bright in appearance and oily. Black patches appearing on the liner surface indicate a leaky piston ring.
- A dry but 'mirror surface' indicate local failure of lubrication as a result of severe galling action. The surfaces were seized and eventually hardened.
- The formation of sharp edges along with the ports and ridge on the top extremity of the piston travel is observed and if exists, to be ground of smoothly.
- When a hard surface due to micro seizure appears on the surface it should be rubbed by a rough grind-stone.
- Any vertical scoring marks should be smoothened by polishing with an oil stone. The horizontal ridge mark should be ground off.
- Cylinder line wear is measured with an inside micrometre length gauge. A reference strip is prepared with holes at measure points that can be held against the liner surface.
- The gauge ensures that the measurements are taken at the same vertical position with respect to liner surface every time at each diametral position the readings are taken along the fore and aft and athwartships directions. The maximum value from these readings gives the wear in the liner.
- For a large bore supercharged engine the permissible liner wear is 0.6 to 0.7% of the original bore.
- For an engine of bore 760mm the maximum permissible wear is 5mm and an ovality of 1mm. For each cylinder, the result should be presented in the form of a graph showing the rate of liner wear with time.
- In engines burning residual fuel, with proper combustion and lubrication by an alkaline cylinder lubricating oil the rate of liner wear should be between 0.05 to O.lmm per 1000 working hours.
- For 4 stroke engines burning distillate fuel or blend with selected residue oil the rate of wear should be much lower, being within the range of 0.018 to 0.025mm per 1000 working hours.
Specific areas of inspection are,
1. Liner Wall
2. Coolant side of the liner.
3. Lubrication Quills.
4. Piston Crown
5. Coolant side of the piston,
6. Piston ring area.
7. Piston rod.
8. Piston Internals.
B. Explain with reasons possible faults which might be found.
i. Excess wear on liner: In-sufficient lube oil, abrasive in the fuel, Liner too cool
2. Cracks on the liner: Fuel impingement (Injection Fault or FO too cold)
3. Deposit on the liner coolant side: Treatment insufficient or oil in water
4. Lubricator quills: Poor or nil operation due or supply system defect
5. Burning and cracking of piston crown: Due to fuel impingement or insufficient coolant
6. Deposit on piston coolant side: FW treatment insufficient or LO depletion
7. Wear of piston rings and grooves: Insufficient L.O, abrasive in the fuel oil, poor combustion (Causes excessive carbon build-up)
8. Scoring of the piston rod: Heavy dirt in the scavenge space. Excess spring tension
9. Cracking of the piston mating surfaces: Caused by incorrect tensioning procedures
C. Suggest how such faults might be avoided.
* Ensure adequate LO supply, clean fuel using separator at low throughputs, operate FW coolant at 80 deg C.
* Regular inspection and testing of the fuel injector, the correct setting of FO viscosity control to 12 cst.
* Weekly checks of FW condition for nitrate measure and low level of chlorides:
* Regular check of flow rate from cylinder LO unit, plus daily consumption.
* Check piston coolant flow alarms,
* Use LO analysis to ensure LO condition maintained correctly.
* Regular checks of combustion efficiency by maintaining the fuel injection equipment properly,
* Regular cleaning of scavenging space and monitor condition of stuffing bore drain.
* Check the intervals of the piston and correctly tenSion piston studs and apply the fastening device.
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