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Serpentine belt versus timing belt

Serpentine belt versus timing belt — what’s the difference?

What does a timing belt do?

People often confuse serpentine and timing belts. They both drive rotating components, but that’s where the similarities end.

A timing belt has cogs that fit into corresponding depressions on the driven components. The cogs prevent the belt from slipping out of time with the driven components and keep the camshafts synchronized with the crankshaft.

What does a serpentine belt do?

A serpentine belt drives accessory components that do not have to be in time with engine components. A serpentine belt is a polygroove (multiple ribbed belt) that’s designed to drive components from both the ribbed and backside of the belt.

All serpentine belts are polygroove (multiple ribs), but not all polygroove belts can be used in a serpentine belt drive system because the backside of the belt is not designed to drive components.

How timing belts work

image shows the difference between a single sided timing belt and doube sided timing belt

Timing Belt Cog Profiles

Timing belt cog profiles differ based on the pulley diameter and rotational force required.

timing belt cog profiles
How a serpentine belt drive system works

A serpentine belt is different than a regular polygroove belt. It has multiple ribs on one side. But the backside of a serpentine belt has a different fabric backing because it’s designed to drive rotating components from the backside as well as the ribbed side.

Look at this diagram to see how a serpentine belt drives components using both sides of the belt.
how serpentine belt works
A serpentine belt typical drives low resistance components using the backside of the belt. So the backside usually drives idler rollers and the water pump.

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