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What Would Happen If a Timing Belt Slipped


Timing belts may be quiet, smooth and inexpensive to pr […]

Timing belts may be quiet, smooth and inexpensive to produce and replace, but you can't help but question the logic of using a piece of rubber to connect the two most vital rotating components in your engine. Fortunately, most timing belts will give some signals before they fail completely; in this sense, the symptoms that accompany a jumped tooth can be something of a blessing in disguise.

Basic Failure

Timing belt failure comes in three flavors, stretching, worn teeth and snapping, generally in that order. All timing belts stretch, and most of that stretch occurs about 15 minutes after installation. A spring-loaded tensioner keeps the belt tight, but after a while the tensioner will run out of travel and the belt will go slack. Simultaneously, the metal teeth on the cam and crank sprockets will slowly round off the edges of the belt teeth, turning those neat teeth into sad little bumps. This, combined with belt slack, will cause the crankshaft to pull ahead of the camshaft. The "retarding" of the cam causes the valves to open and close later than they should.

Exhaust Smoke

If you see the excess exhaust smoke, or even a cloud of black smoke, that means there is something wrong with your timing belt. When the camshaft retards by a few degrees, the intake valve will open and close well after it should. This will quickly dump pressure from the combustion chamber, resulting in an incomplete fuel burn and raw hydrocarbons escaping from the exhaust port. On a computer-controlled car, the oxygen sensor will detect this excess of fuel and the computer will reduce the amount of fuel injected to compensate. At the very least, you'll get a check engine light and a "rich condition" code from the computer.

The timing belt tensioner is part of the internal combustion engine of a vehicle, and it is responsible for keeping the timing belt moving at a consistent pace. The gear and chain systems that connect the timing belt to the crankshaft or camshaft will not work properly if the tensioner is worn, cracked or torn. You should listen for specific noises to know whether there is something wrong with your timing belt tensioner because it is a bit difficult to check the timing belt tensioner without removing them completely.

Listen for a rattling noise. A rattling noise when you start or accelerate could be an indication that there is too much pressure on the tensioner pulley, or that it is cracked.

Listen for rapid changes in rpm when you accelerate at low speeds. If the tensioner is not working properly, it may be very difficult for the car to pick up speed smoothly.

Changing the timing belt on a car should be done every 60,000 miles. This estimate is arrived at through the previous service records for this engine. The 3.0 engine has been determined to be a freewheeling engine in which there is a remote possibility of engine damage if the belt were to fail while operating. Failure of the belt usually means that it stretches beyond the tensioner's limits to keep proper tension on the belt (to maintain timing), but there is also a chance the belt could break.

Remove the accessory drive belts. Remove the cooling fan and the pulley. Remove the alternator and bracket. Remove the crankshaft pulley bolt and the pulley with the puller. Remove the upper and lower timing belt cover. Temporarily install the crankshaft pulley (loosely).

Turn the crankshaft clockwise until the timing marks on the camshaft pulleys are straight up and the mark on the crankshaft sprocket is lined up with the mark on the block which is straight up at 12 o'clock. Remove the tensioner from under the engine. The bolts are going straight up. Remove the timing belt.

Compress the auto tensioner in a vise carefully until the top hole in the rod is aligned with the holes in the tensioner body. Insert a cotter pin through the tensioner body and the rod to keep it compressed.

Install the new timing belt counter clockwise starting on the right side, away from the tensioner at the crankshaft sprocket to the inside of the water pump, around the right camshaft sprocket, then under the idler pulley and over the left side cam. Install the tensioner pulley and torque the bolts to 20 foot pounds of torque. Pull the cotter pin out of the tensioner and allow it to operate.

Rotate the engine two times clockwise and recheck the Automotive V Belts. If the marks are lined up, install all components in the reverse order of removal and torque the crankshaft pulley bolt to 155 foot pounds. You should remove the timing belt and do Step 4 and Step 5 again when the marks are not lined up.