In 2007 a class action lawsuit alleged that Audi knowingly concealed knowledge that their timing belts systems, including those on Audi A4s made between 2000 and 2003 (and possible other years) were not properly designed. The legal action was settled in favor of the plaintiffs, who were compensated for damage and other expenses related to timing belt failures.
Timing belts orchestrate the timing of nearly every moving part in the engine. The primary function is to synchronize the movement of the valve-train on the "top end" of the motor with the movements of the crankshaft on the "bottom end." Timing belts don't tend to be as strong as roller chains. And while metal chains stretch, they're not as prone to stretch and wear as a timing belt. By nature, belts tend to be of lesser quality than chains. The choice of a belt, not just the design and quality, was a contributing factor to the multiple failures on the Audi A4.
Like most modern overhead cam, four-stroke engines, Audi's A4 engine is an "interference engine." This means that during the four strokes of the engine, the piston occupies the same physical space that valves occupy at other times during the strokes. A car running at 4,000 rpm would have to precisely and quickly time the movement of cylinders and valves so they do not collide or "interfere" with one another. Timing belts and chains are especially important in interference engines like the A4's.
Because the A4 has an interference engine, should the timing belt break or even slip, decoupling the timing of the crank shaft and camshaft, the pistons and valves will collide at very high speed with great force. It will cause severe and possibly catastrophic engine damage.
Although plaintiffs in Audi timing belt litigation have been compensated, it doesn't mean every Audi that possessed the faulty components was covered. If you have concern about the viability of an Audi timing belt, one solution is to replace it immediately, regardless of the originally suggested 90,000 mile maintenance interval. Contact Audi for recommended replacements with updated parts
