I believe the camshafts/timing gears are all chain driven - no belts to snap - on all BMW engines whether Petrol or Diesel.
Having once been in a company owned Ford minivan which had a fibre reinforced belt that snapped at less than 4,000 miles and lunched the engine, I try to avoid anything with belt drive. I just don't trust them. Where I have had belts on cars I always change them at around 30,000 miles, or half their stated life if shorter.
Twenty-five years ago I was working on a Police Fleet where we were changing belts every 3,000 miles on one particular engine design as they were failing in use so frequently. I can't remember how many belts snapped in that first year but it was a lot. All covered under warranty, but it must have cost the manufacturer dearly. Strangely we switched fleet vehicle manufacturer shortly thereafter........I wonder why
