3rd class motor question

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Bilge Dweller
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3rd class motor question

Postby ngineer » Mon Jun 29, 2009 2:49 pm

Hello all,

How can you measure the clearance volume for a cylinder of a diesel engine?

The question also asks about how one would measure the bearing clearance of the top and bottom ends of a con. rod, I have an answer for this latter part, but any insight would be appriciated.

Thanks in advance

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The Dieselduck
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Currently located: Nanaimo, British Columbia, Canada (West Coast of Canada)

Re: 3rd class motor question

Postby The Dieselduck » Tue Jun 30, 2009 12:17 pm

The bore of the cylinder times the stroke gives you the swept volume of the cylinder. A MAN B&W K90MCS is an engine with a bore of 900 mm and a stroke of 2,300 mm. therefore 900 mm X 2300 mm = 2.07 cubic meters is the swept volume. From that, it delivers roughly 4,300 kw per cylinder. (http://viewer.zmags.com/publication/d83 ... 83cd0f8/12)

The second part...

Well you can do it by calculation. Putting bearing shells in the connecting rod, torquing them up, then measuring bore; then measure the crank throw, the difference gives you the clearance.
Another way is to use Plastic Gauge, and this website gives you an explanation on how to use. http://www.plastigaugeusa.com/how.html
Martin Leduc
Certified Marine Engineer and Webmaster
Martin's Marine Engineering Page

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Big Pete
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Re: 3rd class motor question

Postby Big Pete » Fri Jul 31, 2009 2:07 am


You were actually asking about the clearance volume of the cylinder, Martin told you how to calculate the swept volume.
The clearance volume is the space above the piston when it is at top dead centre.
The total volume or capacity of the cylinder is the swept volume plus the clearance volume.
The compression ratio is the total volume divided by the clearance volume.

Therefore to calculate the clearance volume you can either:-
Multiply piston area by clearance height (assuming flat cylinder head and piston crown.)
Subtract swept volume from cylinder volume.
From (swept volume + clearance volume) / clearance volume = compression ratio, you can calculate the clearance volume from the compression ratio and the swept volume.

Good luck.
It is always better to ask a stupid question than to do a stupid thing.

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