The airflow through your engine is controlled by a number of mechanisms that are driven by a timing belt or a timing chain, but what is the difference between them?
Distribution chain:
Distribution chains were used exclusively during the early ages of the automotive industry due to their robustness, durability, and simplicity. Most timing chains are roller chains made of steel, similar to the type you would find on a bicycle or motorcycle. The hardness, tensile strength, and modulus of elasticity of steel make it a perfect material for a long-lasting synchro drive system in an engine.
In a motor application, chains require a lubrication system to reduce wear and friction from metal-to-metal contact between rollers and sprockets. The rollers themselves also need lubrication to perform their key function (rolling) as the chain rotates around various sprockets. This helps reduce friction and increase the efficiency of the transmission system. Typically a roller chain is around 97% efficient, which means if it takes 9.7 horsepower to turn the camshaft (s) in your engine at a certain speed , then you will actually need 10 horsepower because some of the power is absorbed into the timing chain due to friction on the rollers.
Advantages of the distribution chain:
- Lower Cost – Camshaft sprockets for timing chains and actual chains are easier to manufacture than timing belt components, which means lower costs for the auto company and you.
- Longer Life – They typically last at least 150,000 miles due to the properties of steel and the continuous lubrication system, which means less maintenance for your vehicle compared to a timing belt.
Disadvantages of the distribution chain:
- Weight – Timing chains are heavier than timing belts due to their steel construction that requires more engine power to overcome inertial forces
- More expensive replacement: Generally, a timing chain is more expensive to replace because the entire chain system is lined with a timing chain cover and valve cover to contain the lubrication system.
- Noise – Chains are always louder than belts due to metal-to-metal contact
Timing belt:
Timing belts were introduced to increase the efficiency of the engines and reduce noise. It consists of rubber reinforced with steel wire that has pinions (semi-cylindrical teeth) that fit into the corresponding grooves of the camshaft and timing pulleys. The rubber belts can naturally flex around the pulleys as they rotate and the contact between the rubber and the metal does not require any lubrication system. Torque is transferred through the gears to eliminate slippage and minimize friction. Timing belts are also very efficient at transmitting power, up to 98%. Its main downfall is longevity.
Advantages of the timing belt:
- Quiet operation – no mechanical connections constantly bending and no metal-to-metal contact
- Lightweight – fewer inertial forces means more power and overall engine responsiveness
- Lower timing belt replacement costs – no need to remove valve cover and pulleys are easier to access
Disadvantages of the timing belt:
- Longevity / Reliability – They only last up to 100,000 miles because rubber wears out faster than steel. Belts are also more susceptible to breaking, which can lead to extremely expensive engine repairs.
- Durability – Timing belt rubber is more sensitive to weather conditions and will not last as long in extreme conditions.
