Large reciprocating engine failures

[enginesrus]

What are some of the failure points in the large 2 stroke engines?
How well does bed plate alignment hold, is there a lot of flexing with the ship hull?
How often do the semi built crankshafts slip and what usually is the main cause?
Is manufacturing quality better nowadays or has it got worse from say 20 years ago?

 

[TugboatEng]

I can say that running aground is likely the main cause for slip in built-up crsnkshafts.

The bedplate of a slow speed diesel is very rigid as it is the point where propeller thrust is transmitted to the hull. It is rare to have to align an engine after the initial alignment. If misalignment does occur it should be detected during routine crankshaft deflection measurements.

 

[gerhardl]

Planning, designing and building knowledge are on a general worldwide basis far better than 20 years ago. On the other side there is probably also a lot more companies and engineers 'trying their hand' on the market without full knowledge, experience and will for first-class production, tests and quality control.

If you produce, design, specify or buy: aim for the best, not the simplest or cheapest. Ask specialists.

If everything is OK, none of your problem areas will come up.

If you have a specific problem, please specify for tips of cause.

 

[CH5OH]

failure modes (I came across):
design and/or initial installation errors:mitigation
-engine build for wrong rotation direction:timing correction on counter ballast weights
-engine oversea shipped with dehumidifier fans wrongly connected:removed internal corrosion/partly repaint
-water cooled piston crowns:I think those engines are of the past, nowadays oil cooled
-pulse loaded scavenging (lots of non return flaps required):abandoned idea (i hope)
associated auxiliary equipment design failures:
-oscillating SW cooler 3 way temperature control valve:seems to be a recurrent design error to want to mount the temperature probe of the valve on feed to the engine rather than on the return of the engine (FW)
-maintenance errors due to a shortage of seagoing people,required skillset is not always adequate
-critical operation:shifting from HFO to MDO and vice versa:risc of pump seizure, fuel blockage because of MDO rinsing of carbon deposits build up over time in fuel system
engine overspeed trip when propellor is tipped out of the water in heavy seas

bedplate alignment, not a problem becuase of sturdy build and sturdy hull section (as narrow as possible to allow for clear water flow to propellor (tighness check of securing bolts/deflection subject to maintenance program (timebased)

would be quite challenging to find a chief engineer who took a ship on her maiden voyage 20 years ago and did so recently again

 

[rob768]

We have seen an occasional shaft failure due to torsional vibrations as a result of poor governor action causing a too slow crossing of the barred speed range.
We also examined a crankshaft which we could identify as a torsional vibration failure, but could not identify the source of these torsional stresses.
Failures related to bed problems I assume are rare (only seen one, many years ago, when they switched from a cast bed to a steel bed)

 

[enginesrus]

Where on the crank shaft were those failures?

 

[rob768]

one was in the radius between crank web and main journal, a second from the slot for the mechanical propeller adjustment, in the intermediate shaft.