Q6. (a) Describe a procedure for cylinder liner calibration, indicating how the readings are recorded to allow for easy recognition of liner wear. (6)
(b) Describe TWO forms of abnormal cylinder liner wear, explaining how each is recognised. (6)
(c)Explain how abnormal cylinder liner wear may be prevented. (4)
>> Some of the critical information that you as second / chief engineer should be aware are given in this Synopsis section. I have also included a graph showing how the liner wears over its life span.
>> Cylinder liner gauging report form is shown, this gives you an idea how liner wear is monitored. If time permits you may include a free hand table in your answer sheet.
>> Gauging figures are noted as total wear from original and mean rate of wear since the last recording was made. The pattern of wear over the length of the liner will differ according to engine type but in a single acting, two-stroke engines it tends to be greatest at the top of the stroke adjacent to the combustion space, where pressure and temperature are greatest. This reduces towards the lower end of the stroke but will increase at the exhaust and scavenge ports when relative pressure on port bars is increased and blow past may remove lubricating oil film. The rate of wear varies over the life of the liner. It is high during the initial running-in period after which it should reduce to an almost constant rate for most useful life of the liner. Finally, the rate will progressively increase as wear becomes excessive.
>> Cylinder liners calibration (measuring the inner dia at various height of the liner is both directions) should be done at fixed intervals during overhaul typically 6000-12000 hours to evaluate the liner wear, any damage, scoring, scuffing, corrosion etc. Continuous records of gauging should be tabulated and maintained consistently.
CYLLINDER LINER GAUGUING REPORT FORM
| Cylinder Number | Date | ||||
| Date cyl installed | Date of last gauging | ||||
| Total Hours | Hours since last gauging | ||||
| Position | Port & Starboard | Forward & Aft | |||
| 1 | |||||
| 2 | |||||
| 3 | |||||
| 4 | |||||
| 5 | |||||
| 6 | |||||
| Maximum Wear | |||||
| Ovality | |||||
| Mean Max wear | |||||
| Wear rate since installation | |||||
| Wear rate since last gauging | |||||
| Remarks
| |||||
2020/OCT? Answered reasonably well.
2019/JUL? Surprisingly, a significant number of candidates could not explain effectively the procedure for calibrating a cylinder liner. Some even missed that part of the question but could answer parts b and c.
>> Cylinder liner calibration is carried out frequently on-board ship (even with extended maintenance periods) and every candidate should have covered this during sea-time. This would suggest that some candidates only answer question from information they acquire at college, or on the internet, and they learn nothing during sea-time.
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