The crankshaft sprocket has worn both on the back face allowing movement of the crank sensor wheel and the alternator pulley towards the engine block as they are attached to the sprocket front face. This is a design issue with the crankshaft and sprocket which was later improved by using a conventional spline shaft and keyway. You probably also have poor acceleration, fuel economy, hot exhaust, overheating, and possible ignition missfire problems that have got progressively worst as the sprocket has worn over time resulting in rotational movement on the crankshaft and resulting bad valve and ignition timing. My car is Kia Picanto Mk1 1.1L 2009 which has the Hyundai engine G4HG common to the Hyundai Getz. As the crankshaft as well as the sprocket is worn I have filled the wear void with feeler gauge superglued to the shaft and then grinded down to size using a dremel as access was limited. I also considered using Loctite660 but was not necessary as the new sprocket fitted tightly. I note some people have added material to the crankshaft with welding and then grinded down to shape. Either way the new sprocket needs to fit tightly on the shaft or the wear will repeat again. In fact it may be necessary to replace the sprocket every 3 years but as the car has already done 55,000miles and the sprocket only costs £16 from Hyundai I can live with that. I have found that Kia are double the price of Hyundai for the same spares and I decided to replace the bolt and crank sensor wheel;-
Sprocket 23120-02570 + Bolt 23127-02530 + Sensor wheel 23141-02610 was £23.39 incl VAT from Hyundai.