Guys, I have a problem getting the alignment correct between the cam and crankshaft. The chain is always half a tooth out of alignment.

I had initially thought that it was that the old timing chain was stretched, but now with a new chain, tensioner and cam sprocket, the same problem exists.

I have checked the thickness of the head, and it is spot on correct at 129mm.

What have I forgotten about??

Would it be best to have the cam timing advanced or retarded half a tooth? (keeping in mind that this car pings and the timing was advanced half a tooth)