## 3rd class motor question

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.
ngineer
Bilge Dweller
Posts: 9
Joined: Thu Feb 19, 2009 4:49 pm

### 3rd class motor question

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.

The Dieselduck
Posts: 3056
Joined: Sun Jul 22, 2007 1:41 pm
Currently located: Nanaimo, British Columbia, Canada (West Coast of Canada)

### Re: 3rd class motor question

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
http://www.dieselduck.net

Big Pete
Engineering Mentor
Posts: 847
Joined: Fri Apr 24, 2009 11:18 pm
Currently located: Solihull, England

### Re: 3rd class motor question

Hi,

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.