FIRING ORDER

Going through the licensing process ? Have queries, comments, or do you need an answer to that obscure exam question ? This is the place to post.
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offshoresnipe
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FIRING ORDER

Postby offshoresnipe » Wed May 21, 2008 2:29 pm

HOW DO YOU WORK THIS PROBLEM?

A FOUR-STROKE EIGHT CYLINDER IN-LINE MEDIUM SPEED DIESEL ENGINE HAS A FIRING ORDER OF 1-5-2-6-8-4-7-3.
IF PISTON #2 IS AT TDC AND IN THE FIRING POSITION, #4 PISTON IS ON THE____________?

THE USCG UNLIMTED EXAMINATION HAS MANY OF THESE QUESTIONS, FOR BOTH 4 AND TWO STROKE, IN-LINE AND V.

HOW WOULD YOU GO ABOUT WORKING THIS PROBLEM? I HAVE LOOKED IN MANY BOOKS BUT JUST CAN NOT SEEM TO FIND OUT HOW TO DO IT.

THANKS FOR THE HELP!!!!!!

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The Dieselduck
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Brain teaser hard on rum intake

Postby The Dieselduck » Thu May 22, 2008 8:59 am

I am sure you know that the answer is A - Exhaust. But getting there took some head scratching. But I believe I got it, but probably would not in an exam. I will try to convey what I did.

The firing order is for an eight cylinder so I assume that each turn of the crank has four cylinder firing, and the others on the exhaust or compression strokes. So all cylinders will have fired every two rev. In the first turn of the crank 1526 are firing, then the next turn of the crank 8473 are firing each at 90 degree intervals. If you had a six cylinder, you would have three firing each rev at 120 degrees apart. This is to make sure the engine balanced.

Start at TDC Cylinder 1 - 1 starts power stroke, 8 starts intake; 90 degree - 5 is on power stroke, 4 intake; 180 degrees - 2 is on exhaust, 7 is in compression; 270 degrees - 6 is in exhaust, 3 on compression.

Crank is finished one rev, so now 8 starts power stroke, 1 starts intake; 90 degree - 4 is on power stroke, 5 intake; 180 degrees - 7 is on exhaust, 2 is in compression; 270 degrees - 3 is in exhaust, 6 on compression

Its more of a mental puzzle, which I hate, personally, but you can work it through logically. If you draw it out it makes a bit more sense.
Martin Leduc
Certified Marine Engineer and Webmaster
Martin's Marine Engineering Page
http://www.dieselduck.net

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offshoresnipe
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Postby offshoresnipe » Thu May 22, 2008 9:52 am

The website marinediesels.co.uk said that the #4 piston is 90 deg. after TDC on the inlet stroke.

I thought I had it figured out early today, but back to banging my head on the desk.

Thanks for your input and help.

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offshoresnipe
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Postby offshoresnipe » Thu May 22, 2008 10:41 am

In the USCG test, the exhaust stroke is the correct answer.

But the test also has many questions that have the wrong answers as the correct answer. The USCG will nottake the time to correct them. So not only do you need to know the correct answer but it helps to know which answer the USCG would like for you to give. Makes for much frustrations, and much drinking!

Regards,
Raymond

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ArkSeaJumper
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Postby ArkSeaJumper » Fri May 23, 2008 5:17 am

I wonder what relevence this has in the real world of working on an engine.

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offshoresnipe
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Postby offshoresnipe » Fri May 23, 2008 5:41 am

I am sure none, but much of the test seems to be like that. We have questions that date to the 70's, use US Navy books with 70's vintage equipment and diagrams that have been photo copied so many times I have lost 10 years on my eye sight. Oh well.

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ArkSeaJumper
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Postby ArkSeaJumper » Fri May 23, 2008 6:50 am

And writing so much you have the wrists of an 80 year old, I know.

These type of questions are the same the world over, I sometimes worry we will end up knowing all the theory about engines but not which end of the spanner to swing.
Ahh well it will look good on paper.


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