if the problem just started after fitting belt or filter then it is a good bet one of these is your problem,if you are sure the timing is correct then make sure your filter is located up into its housing ok,maybe one thing to check if it is smoking very bad with white smoke and it wont cost anything is to remove the rocker cover and check all bolts associated with the rocker shaft and rockers,these come loose and flood the upper chamber with oil and eventually the engine runs on this oil,maybe worth a look
cdc
July 2012