CAMSHAFT DRIVES
7-27. In 4-stroke cycle diesel engines, the camshaft speed must be exactly one-half the crankshaft speed; so
that the camshaft makes one complete revolution while the crankshaft makes two. Since these speed relations
must be exact, the connecting drive must be positive. The drive arrangement used for any particular engine
depends to a large extent on where the camshaft is located. The camshaft may be located low, near the
crankshaft, using long push rods, or on the cylinder block using short push rods, or at the cylinder head level
without push rods (see Figure 7-9). The gears of the drive must be accurately cut and heat-treated to resist
wear. Helical teeth (teeth placed at an angle) are frequently used in place of spur teeth (teeth placed straight)
for greater quietness and more transmission of power. Gears and shafts are used in arrangements to drive the
vital components and accessories of the engine.