Losses in an IC engine

Bearings and drag caused by these parts oscillating and rotating in the vapours in the crankcase.

It all boils down to friction - two ways - reducing the power developed at the coupling and further costing through the need for a cooling system

What about the losses due to accelerating and decelerating the rods and pistons??

The losses specified will be relative to the mass of the items. It also depends on the engine speed, if you want a high revving engine, the friction losses ramp up very quickly and overtake everything else.

In multi-cylinder engines, don't the accelerations/decelerations cancel each other out?

No, you still have to accelerate and decelerate the mass of the components. That's why racing engines use a lot of titanium.

Hi: you should considerer that inertia forces doesn´t work during a cycle. They do a positive work in a part of it and negative in the other. In mechanical terms they are "conservative forces".

Loss of efficiency due to friction about 6%....

"There are many different ways to find the efficiency of an engine, and many different parts of an engine that you can rate the efficiency.

Thermal efficiency is the percentage of energy taken from the combustion which is actually converted to mechanical work. In a typical low compression engine, the thermal efficiency is only about 26%. In a highly modified engine, such as a race engine, the thermal efficiency is about 34%.

Mechanical efficiency is the percentage of energy that the engine puts out after subtracting mechanical losses such as friction, compared to what the engine would put out with no power loss. Most engines are about 94% mechanically efficient.

This means that for a stock engine, only 20% of the power in fuel combustion is effective."

http://ffden-2.phys.uaf.edu/102spring2002_Web_projects/Z.Yates/Zach's%20Web%20Project%20Folder/EICE%20-%20Main.htm

Good link, but still only takes friction as a constant figure.

and the heat leakage, heat radiated and the heat which is blown away by the cooling fan mustn't be forgotten...

http://www.simetric.co.uk/si_cc2hp.htm may be worth a look?