ok so i put my new timing belt and tensioner on, i know the cams are all lined up but when i went to start ,it back fired a few times and didnt start, i also lined up the line on the underdrive pulley with the marking on the engine but i am not sure if it was top dead center... so my question is does it have to be at top dead center and if so how can i tell if it is???? thanks alot.