2003 S4 engine question

It uses a chain - which is a damned good thing considering it is at the *back* of the engine ;-)

They went to a chain because it was narrower than the belt. With a belt the engine didn't fit in.

I thought that relocating the cam drive to the rear of the engine was the space-saving feature. The switch to a chain from a belt was because the new rearward location made regular changes of a belt impractical.

This might be a dumb question, but why doesn't Audi do away with timing belts on *every* engine? FTM, why don't *all* auto manufacturers do away with them? A chain drive -- or even better yet, direct gear drive -- for the camshaft(s) is much more reliable than a belt. No more worrying about whether Audi's service recommendations are accurate; no more multi-thousand-dollar engine repair bills if you ignorantly believe Audi's exaggerated timing belt longevity claims. No longer will essentially complete and immediate obliteration of the engine be the collateral result of a seized water pump or tension roller.

Do chain- or gear-driven camshafts generate too much noise? Do they impose additional drag on the engine? Are they that much more expensive than belts? Or are most automakers simply unconcerned about the long-term reliability of their cars? A cynic would claim that the automakers intentionally build their cars to fail shortly after the warranty period, because vehicle longevity reduces new car sales. Personally, I've never accepted this claim. But sometimes the evidence does seem to point in that direction. There must be a reason why belts continue to be used to drive engines' camshafts (other than Audi's secret desire for all their cars to die 4 years after they're built). Can anyone offer some insight as to what this reason might be?

- Greg

I guess my personal preference for bullet-proof dependability over aesthetics (and even at a modest weight expense) are trumped by others' preferences (for reduced weight and noise) and for other design considerations.

And I honestly hadn't thought about lash in a gear-driven setup. Actually, the only gear-driven cams I've ever seen were on older GM 8-cylinder engines. (I'm not even sure whether they were aftermarket-only or available right from the factory.) They appeared to be indestructible, which is why that design sticks in my head. Perhaps sloppy timing (as would result from excessive gear lash) isn't as detrimental to these older engines as it would be to modern ones.

- Greg