How Belt Pulleys Work | YourMechanic Advice

How Belt Pulleys Work

There are two main types of car pulleys: crank pulleys, and accessory pulleys. Most pulleys are driven by a main crank pulley, which is bolted onto the crankshaft. When the engine is operating, the crank pulley rotates, transferring motion to the other pulleys by means of the serpentine belt or v belt.

Sometimes, the camshaft has power takeoff, with the camshaft connected to the crankshaft by means of sprocket-driven belts or chains. In this case, the accessories powered by the camshaft pulley are also driven indirectly by the crankshaft.

How pulleys work

When one of the accessory pulleys rotates due to drive belt motion, it causes the accessory to activate. For instance, the movement of the alternator pulley causes a magnetic field to form, which is then converted to electricity, causing the alternator to work. The power steering pump pulley causes fluid to become pressurized and circulate, making it easy for you to steer. Most of the time, whenever the engine runs, pulleys will activate accessories. However, there are exceptions. For example, your air conditioning compressor has a built-in clutch, so it spins freely even if your AC isn’t turned on.

Idler and tensioner pulleys are a bit different. They don’t operate accessories, and they don’t provide power. An idler pulley may sometimes take the place of an accessory, or it may simply be included in the serpentine belt system to form part of a complex belt path. These pulleys aren’t all that complex – they consist simply of a cylindrical mechanism and a bearing, and when turned, they spin freely. Tensioner pulleys work in much the same way, but they also work to maintain proper tension on the belts. They use spring loaded arms and screws to apply the proper pressure to the system.

That’s a fairly simplistic overview of belt pulleys in your car. All you really need to know is that without the complex system of pulleys under the hood, your car wouldn’t be drivable.


Next Step

Schedule Oil Change

The most popular service booked by readers of this article is Oil Change. YourMechanic’s technicians bring the dealership to you by performing this job at your home or office 7-days a week between 7AM-9PM. We currently cover over 2,000 cities and have 100k+ 5-star reviews... LEARN MORE

SEE PRICING & SCHEDULING

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Recent Oil Change reviews

Excellent Rating

(21,049)

Rating Summary
19,750
838
175
85
201
19,750
838
175
85
201

Shawn

11 years of experience
121 reviews
Shawn
11 years of experience
Toyota Camry - Oil Change - Lancaster, Pennsylvania
On time. Explained everything that was done and noted an issues that had occurred from a prior oil change that I could take up with the previous garage. I highly recommend Shawn.
Mercedes-Benz C300 - Oil Change - Norristown, Pennsylvania
Arrived on time and was very professional. Helped me diagnose a potential alternator issue. Was very polite and easy to work with.

Pardeep

20 years of experience
812 reviews
Pardeep
20 years of experience
BMW X5 - Oil Change - Santa Clara, California
Pradeep was punctual, informative, knowledgable and professional throughout . I would highly recommend him .
Ford Expedition - Oil Change - Saratoga, California
Called and came much sooner. Did a prompt and neat job. Friendly and very easy to communicate with. Recommend, based on my experience.

Stacy

23 years of experience
281 reviews
Stacy
23 years of experience
Audi A6 Quattro - Oil Change - Atlanta, Georgia
Very, very kind and thoughtful young man! I was very pleased with his demeanor and class! Quite an asset to your Co. Also a good mechanic, thank you for sending him!
Scion xA - Oil Change - Atlanta, Georgia
Quickly rotated my tires & oil change. Let’s me know what is going on with my vehicle during the process. Highly recommended.

Tinashe

12 years of experience
447 reviews
Tinashe
12 years of experience
Mazda 3 - Oil Change - Atlanta, Georgia
I have used Tinashe multiple times for my vehicle service. He is always quick and thorough with his top-quality work. I have never been disappointed!
Ford F-350 Super Duty - Oil Change - Alpharetta, Georgia
Tinashe I feel did a great job as he listened to my request and handled what I needed done. I will be requesting him again.

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

Related articles

How Long Should the Belts in My Car Last?
Automotive Automotive belts these days last quite a bit longer than they once did, thanks to better materials used in the manufacturing process. Just the same, they’re not going to last forever. So if you’re wondering, “How long should belts...
Why Timing Belts Have Teeth and How They Work
Timing Timing belts are used in any number of mechanical devices, but you most often think of this type of toothed belt in connection with your car or truck, where it serves to drive the camshaft. The original timing belts...
How Belt Tensioners Work
The The drive belt tensioner in your car is a small component that works in conjunction with the serpentine belt to ensure that everything in your engine works as it should. From time to time, the tensioner should be checked...

Related questions

Engine cranks but wont start.

From what you've described, it sounds like your timing belt teeth are broken off at the crank gear. You may have bent the valves now since the engine was turning and the cam was not. If this occurs it can...

2004 acura mdx timing belt service: what components do you recommend replacing

Hello, thank you for writing in. When changing the timing belt, it is often recommended to change the water pump, chain tensioner, and the gaskets involved with accessing the timing chain. The price is vary greatly depending on what kind...

What are the chances of my 1.2 i10 hyundai engine valves to be damaged after a timing belt breaks while driving

The Hyundai 1.2 litre motor is an interference motor and the engine is most likely going to bend the valves if the timing belt breaks when the engine is running.

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com