A Matter Of Timing: Timing Belts vs Timing Chains

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Timing belt vs timing chain: what's the diff? Image from Wikimedia Commons

Timing belts vs timing chains: what’s the diff? Image from Wikimedia Commons

Timing belts and timing chains are kind of like gravity, in an odd way; for the most part you never see or hear them, but things wouldn’t work without them. It’s one of the most vital pieces of an engine and as such, the unaware should be made aware.

Timing belts vs timing chains

Some people argue over the relative merits of timing belts vs timings chains, and frankly it’s the sort of thing that doesn’t make much difference to most people. It’s sort of like the whole pushrod vs overhead cam debate; to the vast majority of people, it makes little difference to them.

It might at some point, however, so it behooves…basically anyone who owns a car…to know the difference.

If you’re in the game, then stroke’s the word

An internal combustion engine runs on a four piston stroke cycle, mostly the Otto cycle but a few Atkinson cycle anomalies are out there. The Otto cycle is the one most are familiar with: intake, compression, ignition/power, exhaust. Air and fuel get drawn in, compressed, exploded, gases expelled, all by the motion of the pistons. Said pistons work in a particular order, determined by both the design and the rotation of the cam shaft, which is in turn driven by the engine’s crankshaft.

The crankshaft is connected to the camshaft by – you may have guessed – the timing system. Timing belts and timing chains are how the crank turns the cam.

I get a belt out of you

Ever look at the serpentine belt? All those pulleys and stuff being driven? A timing belt drives the cam the same way the serpentine drives the alternator. A series of tensioners and pulleys are on the motor, which keeps the belt under tension and in place, driving the camshaft.

Chain and Able

A timing chain does the same job, but instead of a belt with pulleys and stuff, it’s a chain. There’s practically no difference from the chain on a bicycle; it’s sprockets being rotated by a chain. The chain itself doesn’t even look much different a bike chain – it’s just bigger and greasier than a cheeseburger walrus.

Where a real difference exists

Well, one thing that might make timing belts vs timing chains worthy of debate pertains to repairs. Timing belts,being made of rubber (though often reinforced with other materials) eventually wear out, meaning they must be changed several times during a car’s lifetime. Since it’s in the bowels of the machine, that means it can get spendy. Replacement every 100,000 miles or less is not uncommon.

Timing chains require replacement much less often, if at all; a timing chain lasting 300,000 miles isn’t that rare.

Pass Interference – automatic first down

There is an ominous corollary. Interference engines, a relatively common design nowadays especially among Japanese brands, are designed so valves protrude into the cylinder chambers during downstrokes, but are removed during upstrokes. This design allows for engines to occupy less space in the compartment. However, if a timing chain or belt breaks, the cylinders and the valves collide. This is while gas and air are being compressed and exploded. It will – no hyperbole or equivocation – wreck the motor. The block itself can be punctured, fractured, or even shorn in half.

So if you don’t recall ever having the timing system serviced…maybe you should.


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