Timing is everything, whether your game is basketball, love or auto repair. Lack of timing can ruin any activity, and nothing will bring a car to a screaming halt faster than a shot timing belt.

As with any of these areas, good technique will assure smooth running. However, industry experts note that there are a number of additional considerations when working on a timing belt repair job.

A quick review: the crankshaft is connected to the camshaft by a belt or chain. This controls the lifting and closing of the intake and exhaust valves at the tops of the cylinders. Since its main job is synchronizing the speed of the crankshaft and the speed of the fuel injection system, it is called the timing belt. It runs on pulleys attached to the ends of the shafts.

Although most mechanics are aware of the function of the timing belt, many are not aware of differences in the tooth properties of today's belts. Jim Donovan, with Gates Rubber Company, Denver, says timing belts come with three different tooth configurations: trapezoidal, curvilinear and modified-curvilinear. "Putting on a belt with the incorrect tooth will damage the system," he warns.

One original equipment manufacturer (OEM, or OE) may choose the square tooth figuring it gives a better grip with less chance of ratcheting. Another engineer will specify a rounded belt for the same reason. "They all work well, but they are not interchangeable," Donovan says.

The trapezoidal profile has square teeth, the curvilinear has rounded teeth, and the modified belt has rounded teeth of a different width. Although the different styles have been out for a couple of years, it is not easy to tell them apart at a glance. While an examination of the sprockets will show the difference between a square belt (two corners) and a rounded one, it takes a real expert to tell the difference between the curvilinear and the modified-curvilinear belts. "The best bet is to go to the OE or supplier and be certain you are getting the right part number," Donovan says, adding that a single digit's difference may be all that separates two belt styles. The car will work for a time with the wrong belt. However, settling for the wrong one almost certainly will spell trouble down the road for the vehicle.

"Now that belt maintenance intervals are typically in the 90,000- to 100,000-mile range, it is important to look at other components in the system," says Jim Kiple, director of technical services with NAPA, in Atlanta. "Look hard at the tensioner and the crankshaft oil seals," he recommends.

Kiple advises against putting on a timing belt without looking at the other components. One key area to check is around the crankshaft oil seals where signs of seeping are common on older vehicles. He also recommends an inspection of the sprockets to be certain that they are in good shape. If the belts are wearing, he points out, it is likely that other components will be worn, too. Dirt and gunk can accumulate around the sprockets. Alignment of the system can go sour, causing a noise problem for the vehicle.

While it varies by manufacturer and model, most problems with timing belts on a typical GM product are likely to be confined to the belt. According to Bill Petersen, technician with Identifix AutoLine, St. Paul, Minn., timing belt problems usually do not result in bent valves. While there have been problems with the V-6 engines which experience belt failure at high speeds, the 4-cylinder engines have been relatively trouble-free. With the 1.8 and 2.0 liter engines, there is little to do other than put the system back into time. Beyond areas that are in direct contact with the timing belt, there is likely to be little corollary damage as the result of a broken belt.

As a rule, idlers are not a problem unless the vehicle has been involved in a collision. GM's idlers are well shielded from road-based damage like flying stones. Still, it is a good idea to check idlers and sprockets to be sure that they spin free and that there is no wobble at the sprockets.

Timing chains In some vehicles - for instance, the classic Plymouth Duster and many of its contemporaries - the belt is actually a chain. Today, timing chains generally are found in higher-displacement engines. With the downsizing of engines, chains became less popular. Where timing belts are liable to wear, timing chains may stretch. Belts are more susceptible to material coming off the street.

A tip for those working on those Valiants with a V-8 engine: use a screwdriver to prevent the camshaft from contacting the freeze plug at the rear of the engine block. This can be done by putting the screwdriver on the backside of the cam gear and pushing so the cam does not move backward.

Donovan says most OEMs are going to belts, if for no other reason than the weight savings in construction. He admits, however, that there always will be a place for chains in diesels. In the case of the Mercedes-Benz diesel, be sure to keep the timing chain in mesh while rotating the camshaft and crankshaft timing gears. When connecting the ends of a new timing chain with the connecting link, be sure to use only rivet-type links. Do not use connecting links, which have a retaining spring. To be safe, check a Chilton or Motor repair manual for the specific model in question.

Whether the job is replacing a timing belt or a timing chain, it generally requires removing the crankshaft drive pulleys and the torsion damper. On most late-model Chrysler products - ranging from the Acclaim to the New Yorker - it will be necessary to put a jack under the engine to support and then raise it. Remove the engine mount bracket, then the timing belt cover. In cases where the timing belt will be used again, be sure to mark on the belt the direction that the belt is running. Generally, this will be clockwise. It's a good idea to put line-up marks on the timing belt and the crankshaft gear to match the drilled mark on the pulley. Re-install the belt so it goes in the same direction. Next, loosen the timing belt tensioner, then remove the belt and crankshaft sprocket flange shield.

When installing the belt, put it on the crankshaft sprocket first. While keeping it tight on the tension side, install it on the ra-diator side of the camshaft sprocket. Finish running the belt, then rotate the engine at the front camshaft sprocket to tension the tension side of the belt. Be sure that all of the timing marks line up, then reverse the teardown procedure to complete the job.

When torqueing the camshaft sprocket bolt, do not allow the crankshaft to move. It may be necessary to shim or block the crankshaft to stop it from moving and assure proper torque.

In the case of many recent models, the timing belt or timing chain case may be cast aluminum, so be careful when handling it. Be sure to check the clearance between the belt and the cover. In a vehicle like the Dodge Colt, this should be within 0.055 inches. Every vehicle has its own eccentricities, which can only be ascribed to the "nature of the beast." Removing the spark plugs from the Mazda Miata, for example, will make it a lot easier to rotate the engine. However, the engine should not be rotated after the timing belt has been removed. It's also a good idea to protect the tensioner with a clean shop cloth before prying on it.

Identifix's Petersen notes that repair instructions for some of GM's 1.8 and 2.0 liter O and K engines are given incorrectly in repair books. They need to be set up before top dead center by 8 or 10 degrees. If the timing is set at zero, the engine will be out of time.

Identifix also recommends checking the edges on the sprockets. Check for malformed edges or anything out of alignment, which would cause the belt to run off center. See if the belt is floating on the sprocket. Sharp edges will tear up a belt or make it ski back and forth. Filing or stoning the edge down can repair minor burrs. However, Petersen notes, failure to replace anything beyond a minor nick is almost a guarantee that the vehicle will be back in the shop. Shops in the North at this time of year may see a seasonal problem. It is not unusual on some models to see snow force its way under the timing belt and make it jump time.

It is almost always a good idea to replace the timing belt when servicing other components. To replace a water pump requires removing the timing belt. Since the job requires disturbing the belt to get at the pump, anyway, all that is involved is the cost of the belt itself. "On any higher-mileage car, you might as well put a new belt on," Kiple recommends.

As with any belts, allowing fluids - whether oil, antifreeze or brake fluid - to come into contact with the timing belt will shorten the life of the belt. In addition to keeping the belt itself clean and dry, avoid putting foreign fluids on the sprockets or the tensioner assembly. In either case, it can rub off on the belt.

The end-game is a properly timed vehicle, out of the shop on time, every time.

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