A. So that they can run at a high rate of speed without exceeding the limit of piston’s travel.
Q. What is the office of the fly-wheel?
A. It maintains a uniformity of motion of the crank, notwithstanding the unequal moving force upon the crank-pin.
Q. Is the force upon the crank-pin unequal, even when the pressure from the cylinder is uniform throughout the stroke?
A. Yes. No matter what the pressure on the piston is, it has no effect in turning the engine when the crank is in line with the guides, which is termed “on the center.” As the crank gets away from the centers, the effect of a given pressure becomes greater, and reaches its maximum when the crank is nearly at right angles with the guides.
Q. How does the fly-wheel counteract the jerky motion of the crank which would result from this?
A. By its tendency to resist an excessive moving force, and by its momentum keeps the engine in motion when the moving force is deficient.
Q. What would you do if the cylinder gets worn or cut from too tight rings or lack of oil?
A. Rebore the cylinder.