It's Not 1965 Anymore

Today's modern engines are using a timing belt (cog belt) and have replaced the traditional timing chain design of yesteryear. Although some engines still use a timing chain design.

Many of my customers confuse the serpentine belt with a timing belt. The external serpentine drive belt is located outside of the engine and drives accessories like the alternator, power steering and air conditioning compressor. A timing belt is located internally under a plastic or metal cover and performs a much more vital role.

The purpose of a timing belt is to connect the bottom of the engine to the top of the engine. I know you're thinking that a bungee cord or a piece of rope could do that. More accurately, a timing belt provides a "timely" connection between the crankshaft (bottom) to the camshaft (top) to ensure that the pistons and valves operate together in proper sequence. Timing belts have proven to be lighter, quieter and more efficient than timing chains.

Today's engines use a "free running and interference fit" design. If the timing belt breaks on a free running design, the engine will stop, you will need to tow your vehicle to a repair shop. A free running design will allow enough clearance between the pistons and valves so that no mechanical damage occurs. The installation of a new timing belt and restoring all of the crankshaft and camshaft timing marks is usually all that is needed to get you back on the road.

If the timing belt breaks on an "interference fit engine" mechanical damage between pistons and valves will occur. Most of the time the damage involves pistons hitting the open valves. This valve damage will require that half of the engine will need to be rebuilt. In extreme cases pistons will be ventilated (holes in the pistons) and the engine will need to be replaced. This is very expensive repair… A.K.A. a "walletectomy."

Proper "proactive" maintenance requires timing belt replacement at regular intervals - before it breaks or wears out. The manufacturers provide a replacement schedule for this critical component…usually (90-120k miles).

Early timing belt designs used a square cut cog design known as a "trapezoidal design." These were the 60k mile replacement belts. Newer timing belts use a rounded cog tooth design known as "curve linear design." This rounded tooth helps the belt last longer.

How do you know if your vehicle has a timing belt or when it should be replaced? Have your qualified mechanic look it up on their information systems - the internet is a great resource tool also.

Qualified auto repair shops will also include related items that are a necessary part of the timing belt replacement. Camshaft and crankshaft seals, water pumps, idler and tensioner assemblies are all part of doing the job right. Moving forward…

Jack Bergan, who has 38 years of experience in the automobile industry, is an ASE Master Technician and a member of the Automobile Service Association (ASA). Send comments or questions to drjack1@mindspring.com Questions will be answered in future columns.

Intensive Care Auto Repair, Inc.