Connecting Rod
The connecting rod transfers the force of the piston to
the crankshaft. It is fastened to the piston pin at the top and
the crankshaft at the bottom. It also causes piston move-
ment on nonpower-producing events (up and down piston
movements). See Figure 1-8.
The small, top end of the connecting rod has a hole
machined in it for the piston pin. The top of the rod
extends inside of the piston.
The big, bottom end of the connecting rod fits around
the crankshaft journal. It has a removable cap that allows
the installation and removal of the rod-piston assembly.
Special rod bolts and nuts hold the cap in place.
As discussed in later chapters, bushings are normally
installed in the small end of the rod. Rod bearings are
installed in the big end of the connecting rod.
Crankshaft
The crankshaft converts the up and down (reciprocat-
ing) movement of the connecting rod and piston into rotary
motion. The rotary motion is used to power gears, chains,
belts, and the drive train.
The crankshaft fits into the main bore of the engine
block, as shown in Figure 1-9. It mounts on the main bear-
ings and is free to spin inside the block. The connecting
rods are attached to the crankshaft journals. Figure 1-10
Chapter 1 Review of Engine Operation 13
Big end
for rod
bearing
Rod nut
Rod cap
Rod bolt
Connecting
rod I-beam
Small end
Piston
pin
Figure 1-8. The connecting rod links the piston and crankshaft
together.The large end has a removable cap that allows the rod
to be bolted around the crankshaft journal.The small end has a
hole for the piston pin.
Main
journals
Snout
Counterweight
Flywheel
flange
Rod
journal
Figure 1-9. The crankshaft takes the reciprocating motion of
the piston and produces rotary motion for vehicle’s drive train
and accessory system.
Piston at
top dead
center
Piston at
bottom dead
center
Rod and
its crankshaft
journal up
Rod and its
crankshaft
journal down
Figure 1-10. Note how the crankshaft changes the recipro-
cating motion of the piston into rotary motion.