What happens if timing belt breaks on 2001 A4 Audi Quattro 2.8?

Answer 1

Since the Audi has an interference engine.

Interference Engines

From Wikipedia, the free encyclopediaAn interference engine is a type of piston engine. Depending on the design of an engine, piston and valve paths may "interfere" with one another as a result of incorrect timing in their movements. (Such designs are also called "interference head" or "non-freewheeling", and include virtually all diesel engines. Conversely, non-interfering engines, such as the Mazda B engine, are called "free-wheeling" or "non-interference" engines.)

In piston engines using poppet valves, the valves descend into the combustion area at the top of the cylinder, while the pistons rise into this area from below. If the lowest point of a valve's descent is lower than the highest point that the piston reaches, the engine is considered an interference engine. In normal operation, the relative timing of the valve and piston's motion prevents them from colliding, but if the valve timing is altered through wear or improper adjustment, or if a valve spring breaks, one or more valves may be placed in the path of a piston.

In interference engine designs, regular belt or chain service is especially important as incorrect timing may result in the pistons and valves colliding and causing extensive engine damage and therefore costly repairs. The piston will likely bend the valves or if a piece of valve or piston is broken off within the cylinder, the broken piece may cause severe damage within the cylinder, possibly affecting the connecting rods. Many manufacturers who were using belts for valve timing have gone back to using chains on new engine offerings, especially on interference designs. However, some non-interference designs have retained belts due to the risk of engine damage from a failure being non-existant. Some manufacturers liked the belt's quietness compared to the chain, and the ability to make additional profits from routine belt service. However, chains, in many cases, last the life of the engine, rarely requiring maintenance and helping to lower the cost of ownership for car buyers who are conscious of that statistic. Also, it was discovered that the sound difference between the two was negligible. During the peak popularity of the belt, chains were used almost exclusively on overhead valve (OHV) engines (which rarely are equipped with belts, regardless of the manufacturer and time of design) and almost all overhead camshaft (OHC) engines received belts. However, chains are now dominant on both types of engines.

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WHEN IT BRAKES...

If your timing belt breaks, the engine will continue to turn, but the camshaft stops. If any of the valves are open, and your engine is an interference engine, the piston will slam into the open valve and cause some real expensive damage. Most modern engines are built with very close tolerances, and to squeeze every last bit of power into a small package, engine manufacturers sometimes create issues with clearances. So make sure you change your timing belt and tensioner if you notice any cracks, wear and tear, dryness.. sometimes it cracks inside the belt rubber so you can't see it, make sure you follow at least the manufacturers service intervals. In addition to cracks, wear and tear on the belts, you can have the same damage done if the belts are too loose, so not necessarily cracked, in which case you will have to tighten them. So you want to avoid a loose belt and or having it brake or you will spend lots $$$ on fixing the engine, something you don't want to do specially on the Audi's.