How a Car Works: Crankshaft

What is the main function of the crankshaft?

To convert the piston's up-and-down motion into rotational motion.

What happens to the crankshaft's rotational motion?

It is transferred to the flywheel and then ultimately to the vehicle's wheels.

What materials are crankshafts commonly made from?

Cast iron or forged steel.

How can you visually distinguish a forged steel crankshaft from a cast iron crankshaft?

Forged steel crankshafts have thicker parting lines.

Around what part does the crankshaft rotate?

The main journals.

What is a journal?

The inner part of a bearing that supports the crankshaft and allows it to rotate with minimal friction.

What components are located between the main journals?

Rod journals.

How are rod journals positioned relative to the main journals?

They are offset from the main journals.

What attaches to the rod journals?

The big ends of the piston connecting rods.

Where do the pistons connect to the crankshaft?

At the rod journals through the connecting rods.

What connects the main journals and rod journals together?

Webs.

What is the purpose of the crankshaft webs?

To connect the journals and support the counterweights.

What is the function of crankshaft counterweights?

To offset the weight of the pistons and help balance the crankshaft.

What is the relationship between crank radius and stroke?

Stroke = 2 × crank radius.

What is engine stroke?

The distance a piston travels within a cylinder.

Why is a well-balanced crankshaft important?

It reduces vibration, improves smoothness, and allows higher engine RPM.

How does oil pressure help the crankshaft bearings?

It creates a lubricating film that minimizes friction.

What feature in the bearings helps create oil pressure?

Oil holes in the bearings.

What can happen to crankshaft journals if oil pressure is too low?

The journals can wear down over time.

What is the purpose of the crankshaft bearings?

To support the crankshaft and allow it to rotate with minimal friction.

Which journals support the crankshaft in the engine block?

The main journals.

Which journals connect the crankshaft to the pistons?

The rod journals.

Main journals = ?

Support the crankshaft and allow it to rotate.

Rod journals = ?

Connect to the connecting rods and pistons.

Webs = ?

Connect journals and carry counterweights.

Stroke = ?

Distance the piston travels in the cylinder.

Formula for stroke?

Stroke = 2 × crank radius.