Replacing a drive belt: does the direction of rotation matter?


Replacing a timing belt is no small task: in most cases, you’ll need to remove the auxiliary belt as well as some accessories. Once the job is done, you’ll obviously need to figure out how to put everything back together. A question that frequently comes up in this context is: is it possible to fit the timing belt and the multi-ribbed belt the wrong way around? In other words: do these belts have a direction of rotation? We’ll answer this question both for the timing belt and the accessory belt. Let’s get to work!

The timing belt: follow the arrows?

From a purely technical point of view, a new timing belt is completely symmetrical, meaning it does not have a direction of rotation. “Then what’s the use of timing belts with directional arrows?”, we hear you wonder. If your new timing belt has timing marks, then there are similar marks on the pulleys/on the engine. The directional arrows are only there to help you line up the timing marks, and it’s by no means obligatory to use them, because – as we’ve said before – a new timing belt can operate in either direction.
Replacing a drive belt: does the direction of rotation matter?  The directional arrows can help you to line up the timing marks.

Re-installing the same timing belt?

If a timing belt is properly installed and the belt tension is correct, you shouldn’t touch it – even if you suddenly notice the arrows are pointing in the ‘wrong’ direction. Once the car has run, it even becomes impossible to remove and reuse the timing belt: unfortunately, it’s good for nothing but the garbage, as a timing belt should only be installed (and tensioned) once.

How about the accessory belt?

With new accessory belts, the story is much the same as with new timing belts: though most mechanics tend to install the multi-ribbed belt in such a way that they can read what’s printed on them (i.e. not upside down). A new multi-ribbed belt is also completely symmetrical and has no direction of rotation.

What does matter, however, is that a used auxiliary belt is always fitted to run in the original direction. So it’s a good idea to draw an arrow on the belt before removing it. If you put the belt back on in the opposite direction, the ribs end up in different pulley grooves than the ones they’ve adapted to over time. This means that the belt has to re-adjust to a new abrasion pattern, which will lead to a dangerous loss of belt tension.

In conclusion, we can safely answer the title question with a confident “no, it doesn’t matter”. Yet automotive technology does not stand still, so it’s not unthinkable that the future will have belts in store for particular applications with a direction of rotation.