Camshaft vs. Crankshaft: What’s the Difference?

Camshafts and crankshafts perform separate functions, but must work together in a well-choreographed sequence for your engine to operate smoothly.

A camshaft uses egg-shaped “cams” to open and close engine valves (one cam per valve), while a crankshaft converts “cranks” (the up/down motion of the pistons) to rotational motion.

What Is a Camshaft?

Located in the “top end” of an engine, the camshaft is a critical part of the valve train that allows air and fuel to enter the combustion chamber (the space above a piston) and exhaust gases out after they burn.

A modern internal combustion engine (IC) can have up to four camshafts — or dual cams — with four valves per cylinder (two intake and two exhaust). A single-cam setup has only one of each valve.

How Does a Camshaft Work?

Driven by the crankshaft, a camshaft transfers motion from the cams through various parts of the valve train to open and close engine valves.

Cam lobes come in different shapes and sizes to control how much a valve opens, and for how long. A four-camshaft configuration increases power. With more valves, more intake and exhaust gases can move more easily because there is more space for them to flow through.

What Is a Crankshaft?

Located in the “bottom end” of an engine, the crankshaft harnesses the tremendous force of combustion by thrusting the pistons downward, causing the crankshaft to rotate. This rotation is the power source of an engine.

How Does a Crankshaft Work?

Connecting rods attach pistons to the crankshaft. Combustion, controlled precisely by ignition and valve timing, exerts massive downward pressure on the pistons, allowing the crankshaft to maintain its rotational momentum.

How Do Camshafts and Crankshafts Work Together?

Camshaft and crankshaft gears are connected by a timing chain or timing belt (similar to a drive belt, but with teeth), or a mesh gear set (two interlocking gears) located in the “front end” of an engine. To control combustion they must be indexed (aligned to manufacturer’s specifications) to work in perfect harmony. This is called valve timing.

During the four-stroke combustion cycle (intake, compression, power and exhaust) the crankshaft turns twice — moving each piston up and down twice — while the camshaft turns once. This results in each valve opening one time for every two crankshaft revolutions in relation to the piston. This way, only the intake valve(s) will open on the intake stroke.

Both valves remain closed during the compression and combustion strokes, and only the exhaust valve(s) opens during the exhaust stroke.

Timing belts, chains and gears wear out, so be sure to check your owner’s manual for the recommended replacement intervals.

Bob Lacivita
Bob Lacivita is an award-winning ASE and General Motors auto technician, vocational educator, Career and Technical Center administrator and freelance writer who has written about DIY car repairs, vehicle maintenance and other self-help topics for more than 20 years.
At the age of 12, Bob took his first engine apart, a 2-cycle Briggs and Stratton from a lawn mower he found in the trash. At 14, he rebuilt a seized 256cu.in. Chevrolet engine in a 1956 Belair that he drove for three years. He spent most weekends, as well as the money he earned working a gas station, at Atco Dragway in Atco New Jersey.
Although trained as an architectural drafter, he never worked a day in that field. Still, the skills he learned helped as he renovated and rehabbed his homes. His true love was cars and so he made that his life’s profession. Bob worked for one of the largest Oldsmobile retailers in the country and earned Pontiac and Oldsmobile Master Technician Elite status as one of the top 20 GM technicians in the country.
Bob was also a Pennsylvania Department of Education (PDE) certified career and technical educator for 25 years, teaching automotive technology for 11 of them. He's been a Certified Vehicle Safety Insructor and an Emissions Inspector, too. Bob earned his master’s degree in educational leadership, as well as his PDE K-12 Principal Certification and his Career and Technical Education Directors and Curriculum Supervisors certificates, to become a school administrator. When it comes to education, Bob has two sayings: The kids are the best part of teaching, and teaching was the hardest job he ever had. It was the best job he ever had, too.
Since retiring, Bob has continued to maintain his ASE Master Technician; MACS Section 609 Refrigerant Recycling Certification; PA safety and emissions inspector certifications, credentials, and licenses; and participated in more than 100 hours of update technical training through MotorAge, Snap-On, Dorman Products and Automotive Technician Training Services, Mitchel1 and others.
Bob currently writes regularly for Family Handyman and works as a consultant with one of the largest automotive retailers on the East Coast, setting up an automotive technology training and apprenticeship program in partnership with a local catholic high school.
Bob and his wife lived through 40 years' worth of DIY home remodeling while parenting two (now grown) boys, and now relax by watching their three fabulous granddaughters.