If i put a weird fuel in my car, it theortetically should not start if 100% of the volume was not gasoline. But also it should not ruin your timing belt as that is an external part of the engine.
Only timing chains are submerged inside the engine getting lubricated by engine oil.
Summary
- Engine should not start if lets say over 75% of the fuel is not gasoline (nothing to combust)
- Incorrect fuel should not wear the timing belt or Exhaust only the internal engine components like spark plugs, piston etc