First Class motor question

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Sébastien
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First Class motor question

Postby Sébastien » Wed Mar 12, 2008 10:57 am

I am currently studying for my first class motor knowledge examination and found an interesting question: "How would you know if a piston was in danger of seizing?" Well I always thought you wouldn't know until it happened and would be neck deep in doo-doo. Any hints on this one?

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Postby JK » Thu Mar 13, 2008 2:36 am

I would expect it is more to what would cause piston siezure.

Loss of liner lubrication-manzoll lubricator
Wrong liner material and rings-chromed
Loss of piston cooling
Overheating

and so on

As opposed to the "oh shit" moment when you actually have the piston on the deck and see the scores.

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Postby Sébastien » Thu Mar 13, 2008 7:24 am

Thanks JK, I hadn't seen it that way.

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Gudgeon Pin crack

Postby The Dieselduck » Thu Mar 13, 2008 9:45 am

I've also experience an intermittent increase in liner temp, especially after warming up. On the Wartsila 46, this seemed to be a pretty good indicator that the gudgeon pin (wrist pin) was cracked. Not really overheating, but if you suspected something, you just monitored that liner after startup, and you could see the temp would rise slightly above norm. Over time you learn to recognize this.

On our engines there were three heat sensors on the liner, so we could get a pretty accurate picture of what was going. See picture, the alarm point is suppose to be around 150, I think, but we kept ours around 130 to pick up this problem at the earliest time. You can see under full load that your temps are around 120. On the suspect cylinder the temp would climb up to 127-130 then settle down after 30 minutes or so, over time gradually reaching a higher peak and steadiness.

I think one hole did seize once, but otherwise we caught them in time and pulled the piston and magnaflux the pin to find the crack.

My two cents.

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Postby JK » Thu Mar 13, 2008 12:58 pm

It is a good management type question. Is the candidate going to analyze the engine operation and see that the outcome will be piston siezure and act on it appropriately.
That is how to approach all the questions on the 1st.
The other thing is if you get questions about a letter to management, be very careful on how you answer it. These are usually a trap for the orals.

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Postby D Winsor » Fri Mar 14, 2008 4:02 am

It has been my experience on medium speed engines the oil mist detector is one of the best indicators of an imminent piston seizure.
Aluminum particles in oil filters is another good indicator. This is will indicate that there may be scoring between the piston skirt and the liner. or a problem with a bearing that could cause a loss of piston cooling.
An increased crankcase pressure, excess crankcase venting, unexplained oil leakage around shaft seals and explosion doors are good indicators of something is amiss.
Any of these symptoms should be followed up by a good old fashioned "Crankcase Inspection" as soon as possible to give the best indicator of all "Your eyes" to find the problem before you end up in deep DOODOO
Last edited by D Winsor on Fri Mar 14, 2008 11:15 am, edited 1 time in total.

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Postby Sébastien » Fri Mar 14, 2008 4:47 am

OK, now you have got me curious JK. How can the letters to management be a trap for the orals? I hate those letters to management questions, I always get the feeling that I am forgetting to mention something obvious that they want to see in my answer.

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Postby JK » Sat Mar 15, 2008 12:21 pm

I had to think about this because it is been a few years since I have looked at the questions.
When you write your letter to the office, you have to consider all the implications of what you write and will the Examiner be able to question your further.
If it is a death, what was the work orders, safety plan; machinery failure, why did it fail and how come you,as a Chief did not foresee the failure.

There is a question about 200 tones of emulsified bunkers for example. Why did it become emulsified? Did you take samples of what was taken on? Why did the purifier fail? Where did the water come from? If it was a leaking line, why did it run thru a fuel tank and why didn't you as the Chief see that the level in the tank was rising. If it was bunker incompatibility, why wasn't the fuel managed differently.
So on and so forth. In fact I would never have answered that particular question, because even with help from a good friend who worked on tankers for years, I could not come up with a satisfactory answer that I thought that would not lead to further questions in the orals.

There is another one about LO being contaminated, that one I did manage to come up with a true scenario that I thought would be suitable for an answer.

When I did my Chiefs, I did the most work on the letter questions, trying to foresee what the Examiner would ask in the orals. Much to my surprise, I didn't have a single one.

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Postby Sébastien » Sat Mar 15, 2008 3:16 pm

Thank you again JK. Believe it or not, my first class general examination had three out of nine questions that were letters to the company, including the one about a death in the engine room. One of the questions was justifying holding on to extra parts after receiving orders from the office to reduce on board stores to classification society minimum requirements. To me this is an absurd scenario, the only reason I can think of that a company would issue such an order is if the ship was scheduled to be sold or scrapped and the spare parts sent to a sister ship in the same company. Any thoughts, oh venerable guru?

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Postby JK » Sun Mar 16, 2008 2:48 am

Venerable guru, ACKkkk :shock: I will have you know my walker is still at the dealers!!

This is a new question, first time I have seen it. I'll bet ArkSea Jumper would have some excellent thoughts on this topic.

All the good engineers I deal with have a common attribute: they want a perfect ship and they want all the goodies to make it perfect. Then they hoard the goodies.
For instance a Chief goes back on a ship after 10 years, reviews the records and says I need 5 heads for the SSGs because they have a record of cracking. That is about $130,000. However the problem is not the generators but the fact they had had water in the fuel and this cracked the injectors and then the injector pocket. If the FOP is working correctly and the day tank drained, then they have no head problems. Now, conceivably, we have 5 heads stored on the ship in nooks and crannies, subjected to whatever handling the crew gives them, rough weather and dampness. They could be useless by the time it comes to use them or, which happens more, the knowledge is lost that they are onboard and more heads are ordered. They are not available to other ships of the fleet with the same model engine.
If you multiply this thinking across a fleet of ships, this is a huge investment in sparing.
Now I'm going to go off into fantasy: if the ship engineers are running a good predictive maintenace and preventative maintenace program, they will be able to schedule maintenace and bring in parts. Good predictive maintenance reports allow for extension in surveys ( anyone can correct me here, our ships are not delegated to class, so this may not be true )

The other thought I had, was less weight carrried in stores, the more room for cargo and the more money made on a voyage. The beancounters don't actually have to sail on the ship after all and it is all about profit! Can you imagine the lobbying to Class to get minimum sparing onboard!!

The other thing is you move the Supply Chain Management off of the ship into the office. We all know in this day and age, the Chiefs and Captains are swamped with ISM, ISPS and whatever other new policies come up. With minimum manning, there is no one to deal with the sparing onboard and it would not take long to be in disarray and no one have a handle on it at all.

Saying all that, we had a Zim ship come in here around Christmas. They had taken on bad fuel their last port of call and had severely worn all of the liners and piston rings in the main engine. A local company had been called in to work on the engine, they honed the liners and installed new rings, but it was a temporay fix-all 6 liners had to be replaced and there was only one available in Portugal. Large engine spares have a huge lead time in ordering. If the companies supply chain had not foreseen that they could not get parts in for 18 months or so and not taken steps to minimize the problem, then the ship is out of service
(or would it, Class does not give me a warm fuzzy feeling and it appalls me that TC has handed their mandate off to them)

Just some random thoughts. I'm glad the Examiner isn't reading this :D

I will tell you though, I am glad I didn't get 3 'bank letters' in my exam.

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Postby Sébastien » Sun Mar 16, 2008 5:39 am

Thank you again JK, I was just teasing you (I knew I would get a reaction from that one). I have experienced first hand most of what you have said about spare parts held on board, one of my pet peeves is finding a damaged part in spare parts stores with the caption "used but good".

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Postby JK » Sun Mar 16, 2008 9:42 am

Hah, I've been bushwacked :evil: Next it will be senility.
And for the used but good parts, it always seemed to be the older guys that did that. I expect they had learned it from their Depression era parents. I always made sure I snapped whatever part I was replacing to make sure it wouldn't make it back into stores.

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Postby Sébastien » Sun Mar 16, 2008 12:13 pm

Many spare parts were discarded, when someone asked why they were scrapped the reply was that they "Failed the float test"

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Used but good...

Postby The Dieselduck » Mon Mar 17, 2008 4:05 pm

.....oooooh I hate "used but good". Although it goes against my "grain" i have to sometimes break stuff definitively, or give it the float test, so it doesn't wind back up on the shelf as ballast that will just get in the way of finding the real part you need.
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UBG's

Postby conrod » Mon Mar 17, 2008 11:09 pm

Gents,

Now come on, have you not been on a ship, where a UBG saved you bacon ?? Here is a good one for you.

I was 3/E with a Hong Kong chappie as 2/E. He had a reputation for hording purifier O rings. The Alladins Cave was full of them. Big HFO Alfa Laval's, so the bowl O rings were not small. I came across these one day whilst looking for some piston rod stuffing box spares. I did find my spares, but also a useful tool for splitting rings. O rings were way better than little bits of rag across the ends of the scraper rings !!

Oh what fun we had in those days. They also made pretty good sling shots.


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