Timing Belt
 

Started working on an old Isuzu that was my grandfather's 1998 amigo 2.2l. So I have replaced the timing belt on roughly a dozen other vehicles, I am no expert. The car has 2.2l GM 4banger in it. It was not running but after replacing a couple of parts and fixing others it ran for roughly 40 miles and the timing belt snapped. I have tried endlessly to time it correctly using the marks and all information possible online with a new belt, but I have no idea what to do with no luck. After numerous tries it's always the same result everything runs fine, but you can hear the valves coming into contact with the pistons as the timing is off. Is there something I am missing, is this a common problem hopefully I can get some assistance, thank you.