The flow of air through your engine is controlled by a series of mechanisms that are driven by either a timing belt or timing chain, but what is the difference between them?
Timing chains were used exclusively throughout the early ages of the automotive industry due to their ruggedness, durability and simplicity. Most timing chains are roller chains made out of steel, similar to the type you would find in a bicycle or motorcycle. Steel’s hardness, tensile strength, and modulus of elasticity makes it a perfect material for a long lasting timing drive system in an engine.
In an engine application the chains require a lubrication system to reduce wear and friction from the metal to metal contact between the rollers and the sprockets. The rollers themselves also need the lubrication to perform their key function (roll) as the chain rotates around various sprockets. This helps to reduce friction and increase the efficiency of the drive system. Typically, a roller chain has an efficiency of around 97% which means that if it takes 9.7 horsepower to turn the camshaft(s) in your engine at a certain speed, then it will actually take 10 horsepower because some of the power is absorbed within the timing chain due to friction in the rollers.
Timing Chain Advantages:
- Lower cost – the camshaft sprockets for timing chains and the actual chains are easier to manufacture than timing belt components which means lower costs for the car company and you
- Longer life – they typically last at least 150,000 miles because of the properties of steel and the continuous lubrication system which means less maintenance for your vehicle compared to a timing belt
Timing Chain Disadvantages:
- Weight – timing chains are heavier than timing belts because of their all steel construction which requires more power from the engine to overcome inertial forces
- More expensive replacement – generally, a timing chain is more expensive to replace because the whole chain system is encased by a timing chain cover and valve cover to contain the lubrication system.
- Noise – chains are always louder than belts because of the metal to metal contact
Timing belts were introduced to increase the efficiency of engines and reduce noise. It consists of steel wire-reinforced rubber that has cogs (semi-cylinder teeth) that fit in the corresponding grooves of the camshaft and timing pulleys. The rubber belts can naturally flex around the pulleys as it rotates and the rubber to metal contact requires no lubrication system. Torque is transferred through the cogs to eliminate slippage and minimize friction. Timing belts are also very efficient at power transmission – up to 98%. Their main downfall is longevity.
Timing Belt Advantages:
- Quiet operation – no mechanical linkages that are constantly bending and no metal to metal contact
- Lightweight – less inertial forces means more overall engine power and responsiveness
- Lower timing belt replacement costs – valve cover removal is not necessary and the pulleys are easier to access
Timing Belt Disadvantages:
- Longevity/Reliability – they only last up to 100,000 miles because rubber wears faster than steel. The belts are also more susceptible to breakage which may lead to extremely expensive engine repairs.
- Durability – the rubber in the timing belts is more sensitive to weather conditions and will not last as long in extreme conditions.