I know this is an old thread but it has a lot of tribal knowledge built up in it now. Something i learned this weekend. If you have set the crank, camshaft and flywheel to all the timing markings correctly and you fire up your motor and it sounds like a popcorn machine, don't panic. I recently just had to replace my camshaft seal and went through this. Turns out I didn't tighten down the timing belt tension pulley. Of course I had by then pulled all the covers again and the main pulley before I figured it out. Once I rotated the belt and then tighten down the pulley all was fine.
