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Can an auxiliary belt damage the timing belt

This is the scenario I’m getting from my mechanic. I bought a 1998 Volvo V70 wagon with 120k miles on it about a year ago. Recently, my wife was driving when she lost power.

After we towed the car to the shop, I popped the hood and saw that the auxiliary belt was shredded. I was worried about the timing belt, so I asked him to check and replace.

The timing belt was not snapped, and they started work. Later that day, I got a call to say that the auxiliary belt must have gotten caught up in the timing belt, shearing off some teeth, throwing off the timing, and bending/breaking valves. So now I need to replace the head.

Is this possible? I thought the timing belt was completely covered. Or was it damaged during the repair?

I wonder if it’s the reverse scenario.
The timing belt took out the fan belt.
When the timing jumped and the cam and crank were arguing with each other, the difference in rotation speeds caused the fan belt to jump into things that shredded it.
They replaced the fan belt first not noticing the timing belt issue until the attempt to restart.

(Just a guess as I’m not a tech, just a partsman )

I have to admit that this was my initial fear, and why I asked him to check the timing belt and replace it. I would think that he would have told me that the timing belt had missing teeth when they first took it off, not after putting a new belt on (and the auxiliary belt, I imagine) and trying to start the car.

The timing belt probably just jumped teeth first. They didn’t notice ( or check ) the timing marks were off. The next attempt to start then sheared teeth.

The timing belt is under a cover. The auxiliary belt is the one you see when you lift the hood.

Under normal conditions there’s no way for one belt to interfere with the other. Is the timing belt cover intact? You didn’t say it was damaged, so I’m assuming it’s not.

Something doesn’t add up here.

Actually, on this 5-cylinder engine, the timing belt cover is open on the bottom side around the crank pulley. It is not fully enclosed. The belts can possibly interact if one jumped the grooves.

When you bought that car, did it come with maintenance records?

I ask because if you could not confirm that the timing belt had been replaced on schedule, it was already grossly overdue for replacement a year ago when the car was 10 years old with 120k miles on it. When used cars do not come with maintenance records, you must assume that vital maintenance has not been done.

I suspect the repair cost will exceed the cars value…

Well, in that case the shredded accessory drive belt could have damaged the timing belt.

…which is a perfect example of why maintenance is invariably cheaper than the repairs that result from skipped maintenance!

The failure of the aux belt is prime suspect that lead to the failure of the timing belt whether factory installed or replaced recently.

It appears to be a poor design or just the bad luck case that a failed aux belt can ruin a timing belt in a interference engine application.