Belt should be replaced at 100000klms, you should also replace tensioner and idler pulleys, and it is a good idea to replace cam and crank seal. You can purchase a kit from repco, coventrys or most parts shops that contain all you need. check the crank and cam shafts for wear under the seals (ie groove) you may need to speedi sleeve the shafts if they are worn. to speedi sleeve the crank you will need to be carefull and reverse the sleeve (ie fit it the other way round) to get it to fit.