Timing belt vs serpentine belt comes down to the job each one does: a timing belt keeps the camshaft turning in step with the crankshaft, and a serpentine belt drives the engine’s accessories. One has teeth, the other has ribs.
A timing belt is also called a cam belt. Below you will find what each belt does, a side-by-side table, four checks to tell which one you have, and how their failure signs differ.
Key Takeaways
- A timing belt keeps the camshaft in step with the crankshaft. A serpentine belt drives accessories such as the alternator and the water pump.
- A timing belt has teeth, and a cam belt is the same part. A serpentine belt is multi-groove, with ribs.
- Teeth lock a timing belt to its pulleys. A serpentine belt grips by wedging into the pulley grooves.
- A broken timing belt means the engine will no longer work. A broken serpentine belt stops the alternator, water pump and power steering pump.
- Many newer cars use a timing chain, so check the owner’s manual before you assume there is a timing belt.
Table of Contents
- What a timing belt (cam belt) does
- What a serpentine belt does
- Timing belt vs serpentine belt: key differences
- Timing belt or serpentine belt: which one is on your engine?
- Failure signs compared
- FAQ
- About Longyi Rubber Products Factory
What a timing belt (cam belt) does
A timing belt is a toothed belt that drives the camshaft and synchronizes its rotation with the crankshaft, so valve timing stays matched to piston position (Wikipedia on the camshaft timing belt). The AA on cam belts says a timing belt is just another name for a cam belt.
Teeth on its inner surface mesh with the crankshaft and camshaft pulleys, and toothed belts do not slip when correctly tensioned (Wikipedia on toothed belts). The belt usually sits at the front of the engine, often behind a cover that keeps out dust and debris. On some engines it also drives the water pump or other parts (Samarins on timing belts).
For tooth profiles, materials and failure modes, see how a timing belt is built and how it fails.
What a serpentine belt does
A serpentine belt, also called a drive belt, is a single continuous belt that drives several accessories at once, such as the alternator, power steering pump, water pump and air conditioning compressor (Wikipedia on the serpentine belt).
An idler pulley and/or a belt tensioner guides the belt, and the crankshaft provides the initial rotation. The belt is almost always of multi-groove (multi-vee, poly-v or multi-rib) construction.
Family Handyman’s serpentine belt guide says a single serpentine drive belt replaced two, three or more V-drive belts. The other names for this belt family are on the page about multi-V, poly-V and serpentine belt names.
Timing belt vs serpentine belt: key differences
| Feature | Timing belt (cam belt) | Serpentine belt |
|---|---|---|
| Main job | Keeps the camshaft turning in step with the crankshaft, which keeps valve timing correct | Drives engine accessories such as the alternator, power steering pump, water pump and air conditioning compressor |
| Inner face | Teeth that mesh with the crankshaft and camshaft pulleys | Grooves or ribs along the belt (multi-groove, poly-V or multi-rib) |
| How it grips | Teeth engage the pulleys; no slippage when correctly tensioned | Ribs wedge into the pulley grooves; an idler pulley and/or tensioner guides the belt |
| Where to look | Front of the engine, often behind a cover | Around the accessory pulleys; the routing diagram is usually under the hood |
| Overlap | On some engines it also drives the water pump | The water pump is one of the accessories it drives |
| If it fails | The engine will no longer work; in an interference engine the pistons can strike the valves | The alternator, water pump and power steering pump stop; the car is quickly unusable |
| Warning signs | Metal-reinforced rubber belts give no indication of impending failure; ticking noises, misfires, hard starting or smoke call for a check | Cracked, glossy or frayed ribs, rounded rib profile, chirping or squealing; a worn belt can also slip without the usual squeal |
| Replacement basis | The maker’s interval, counted by mileage and by belt age | Rib wear and cracks, checked by eye and with a wear gauge |
Each row is explained, with sources, in the sections of this page.
The two belts grip in different ways. Teeth engage the pulleys on a timing belt, so it holds the engine’s timing. Dorman Shop Press on serpentine belt wear gauges says a serpentine belt relies on a wedging effect to transfer power to the driven accessories, and a worn belt can slip, may not make the characteristic squeal, and runs hotter.
On some engines the timing belt also drives the water pump, and the serpentine belt can drive the water pump too. Sharing a pump does not make the two belts the same part.
Timing belt or serpentine belt: which one is on your engine?
Use these four points to find out which belt you are dealing with.
- Look at the inner face. Teeth mean a timing belt, and grooves or ribs along the length mean a serpentine belt.
- Follow the route. A serpentine belt runs around the accessory pulleys, and Family Handyman’s serpentine belt guide says its routing diagram is usually under the hood and may also be in the owner’s manual.
- Look for a cover. A timing belt is often behind one, and Samarins on timing belts says a mechanic might have to remove one of the covers to inspect it.
- Find out whether the engine has a timing belt or a chain. Many newer cars use a chain, so check the owner’s manual, or ask a dealer service department or a mechanic.
The AA on cam belts says some manufacturers now use wet belts which, like timing chains, run inside the engine in the engine oil. The page on wet timing belts covers them.
If you source either belt, the LYBELT range includes automotive timing belts and automotive ribbed belts. Send the belt code, a photo or a drawing.
Failure signs compared
On a serpentine belt the signs are on the ribs: rounded, flattened, cracked or frayed ribs and a glossy face all point to wear (Family Handyman’s serpentine belt guide). The eye can still miss it, because Dorman Shop Press on serpentine belt wear gauges says EPDM serpentine belts do not show visual wear until long past their useful life. The full checklist is on the signs of a bad serpentine belt page, and the steps are in how to replace a serpentine belt.
A timing belt leaves less of a trail. Metal-reinforced rubber belts give no indication of impending failure (Wikipedia on the camshaft timing belt), and internal deterioration is not considered reliably detectable (Wikipedia on toothed belts). AAA on when to replace a timing belt lists engine misfires, difficulty starting, engine ticking noises, and smoke or fumes from the engine as reasons to have it checked. Service life is measured by mileage and by belt age (Tomorrow’s Technician on mileage and belt age), so the maker’s schedule decides, not a look at the belt; the timing belt replacement interval page shows how to find it.
The two belts can also affect each other. The AA on cam belts says that if an auxiliary belt shreds, fibers can get trapped under the timing belt because both run off the crankshaft pulley, which usually makes the belt jump or come off.
FAQ
Is a serpentine belt the same as a timing belt?
No. A timing belt is a toothed belt that keeps the camshaft in step with the crankshaft, so valve timing stays matched to piston position (Wikipedia on the camshaft timing belt). The serpentine belt is a separate multi-groove belt that drives the engine’s accessories.
What is the difference between a timing belt and a serpentine belt?
One is a toothed belt that times the valves to the pistons, and the other is a multi-groove belt that drives the accessories. Teeth lock the timing belt to its pulleys and it does not slip when correctly tensioned (Wikipedia on toothed belts), while the serpentine belt grips by wedging into the pulley grooves.
Is a cam belt the same as a timing belt?
Yes. The AA on cam belts says a timing belt is just another name for a cam belt, the same toothed belt that is part of the internal combustion engine. Because the two names mean the same belt, cam belt vs serpentine belt is the same comparison as the one on this page.
Can a car have a serpentine belt and a timing belt at the same time?
Usually the accessories run on a serpentine belt, which Family Handyman’s serpentine belt guide calls standard on virtually all makes and models. The valve timing runs on a belt or a chain, and many newer cars use a chain, so check the owner’s manual.
What happens if a timing belt breaks compared with a serpentine belt?
A broken timing belt means the engine will no longer work, and in an interference engine the pistons can strike valves left open (Samarins on timing belts). A broken serpentine belt stops the alternator, water pump and power steering pump, so the car is quickly unusable because of lost engine cooling.
Which belt makes a squealing noise, the timing belt or the serpentine belt?
Family Handyman’s serpentine belt guide says chirping or squealing noises are a reason to replace a serpentine belt. Engine ticking noises are on AAA’s list of reasons to have a timing belt checked. Noise alone is not a diagnosis.
Sources
- Wikipedia on the camshaft timing belt
- The AA on cam belts
- Wikipedia on toothed belts
- Samarins on timing belts
- Wikipedia on the serpentine belt
- Family Handyman's serpentine belt guide
- Dorman Shop Press on serpentine belt wear gauges
- AAA on when to replace a timing belt
- Tomorrow's Technician on mileage and belt age
Source names appear here only as references. LYBELT is not affiliated with them.
About Longyi Rubber Products Factory
LYBELT is the brand of Longyao County Longyi Rubber Products Factory (General Partnership), based in Longyao County, Xingtai, Hebei, China, and making rubber belts since 1999. The factory holds IATF 16949 and ISO 9001 certification and works from 130+ rubber compounds.
The range covers automotive, industrial, agricultural, ATV/UTV and motorcycle belts. For OEM and ODM orders, belts are made to the customer’s part number, drawing or size, with private label and packaging. Email: luxin@lybelt.com.