Couldn't tell you. You can't over tighten it it has a tensioner that presets the load. if you didn't request the water pump and pulleys to be replaced they probably weren't and that could be the issue. However that's not on the shop.
Yes, the engine could require a rebuild. On an interference engine there is the likely hood that a valve could impact the piston. Best case scenario it failed where nothing hits. Mid case scenario it hits a valve and bends it and only the heads need rebuilt. Worst case scenario valve hits piston damages the piston, breaks off damaging the head and cylinder walls.
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