Originally Posted by BimmerM3inGA

It has to be exactly spot-on. The engine will run without damage if it's off a bit, but you'll have a rough idle and it will throw codes to activate the Check Engine light. So you'll have to open it back up and redo the timing.

If you follow the Beisan instructions to the letter and pay very close attention to the final cam timing, it will be correct. It's kind of hard to describe out of context, but there is a way to verify that the timing is correct prior to buttoning it up. With all the fixtures still in place, you rotate the intake cam counterclockwise manually to the fully retarded position and measure how much the rear cam locking block lifts off the head. Anything more than 1mm is too much. Again, it doesn't make much sense out of context, but it's pretty clear when you're actually looking at it. As long as you have that measurement within spec, you'll have no doubt that the timing is spot on. But of course, you want to rotate the engine by hand through several revolutions - just to make sure!

FWIW, unless you know for sure that the chain guides are broken you don't HAVE to do this job. What I plan to do on my 4.6is is to monitor them and only open up the engine if I see evidence of the guides failing. The Bank 1 valve cover gasket is leaking pretty badly, and it's also due for an oil change. So, my plan is to remove the lower oil pan when I change the oil. If there are bits of plastic in the pan, I'll know it needs new guides. I'll also visually inspect the guides when I change the valve and timing cover gaskets. And then I'll remove the oil pan every time I change the oil. If/when I start seeing pieces of the guides in the pan I'll replace them.