Timing Belt and Chain Replacement Manassas, VA

The best way to approach this subject is to begin by explaining why engine timing is so important in a four-stroke internal combustion engine.

The four-stroke combustion process has an intake stroke, a compression stroke, a power stroke, and an exhaust stroke. Throughout this cycle, the camshaft spins once and the crankshaft rotates twice. Timing belts control the movement of the crankshaft and camshaft(s), also known as “mechanical timing,” which opens the valves at a precise time in conjunction with the pistons. The engine won’t work properly, if at all, if the timing is off.

No discussion of timing belts/chains would be complete without a few words about interference engines. An interference engine is one in which the valves and pistons occupy the same space in the cylinder – but not at the same time. If the timing belt/chain breaks, the valves and pistons could end up in the cylinder at the same time. While they can share the same space, even multiple times in a second, they can NEVER be there at the same time. In other words, the valves and pistons should never meet. You don’t need to be a mechanic to know that if this happens, the outcome will not be pretty.

On a non-interference engine, the belt/chain could break and not cause extensive internal damage because the pistons and valves are never in the same place at the same time.

Please give Coho Auto a call if you’re not sure which engine type you have.

Timing Belts

A timing belt is, like the name implies, a belt much like the other “serpentine” belts on your car’s engine. Made of rubber and high-tensile fibers, they are quieter, lighter, less expensive and much easier to replace than timing chains. (They are also less durable than timing chains.) The timing belt runs through a series of pulleys that have belt tensioners in place and usually wear out at the same time as the belt. This is why most manufacturers and mechanics recommend that you replace the belt tensioners and water pump at the same time.

Timing Chains

A timing chain is a roller chain, much like the chain on your bicycle. It is made of steel plates and spacers, with steel pins holding the plates (chain links) together. Timing chains serve the same purpose as a timing belt, but they are more durable, heavier, and last longer than timing belts. (They are also more expensive and troublesome to replace.) Since they have nothing to do with one another, the water pump is usually not replaced at the same time you replace the chain.

Because it is a metal-on-metal system, a timing chain requires lubrication. A timing chain also has tensioners that keep it in place, but unlike belt tensioners, the oil pressure in the engine controls timing chain tensioners. So, if your oil pressure becomes too low, the tensioners will fail, the timing will offset, and the chain will likely fail in a spectacular fashion.

As noted above, if your timing chain breaks, it will usually cause a lot more damage than a broken timing belt. Not that we’re suggesting a broken timing belt isn’t going to cause you problems – it definitely will. But with a broken belt, you might get away with just having the heads done. If the chain breaks while driving at speed, you will have to replace the whole engine.

Proper Maintenance of Timing Belts and Timing Chains

Automotive maintenance schedules exist for a good reason. Oil needs to be changed at regular intervals. Spark plugs need to be changed at certain times. And no less important, timing belts and chains need to be changed according to the manufacturer’s guidelines.

With proper vehicle maintenance, it’s not likely that you’ll experience problems with your timing belt or chain. If your vehicle manufacturer recommends replacing the belt or chain at a certain point – usually based on miles – do it! Neglecting this important maintenance item is very risky, and depending on the age of your vehicle, could result in repairs that exceed the car’s actual value. If you bought a used vehicle and you’re not sure if your timing components have ever been replaced, give Coho Auto a call to set up an appointment.