I am replacing my timing belt. First I put the engine at top dead center for cylinder 1. Then I marked the positions of the crankshaft cog and the camshaft cog with paint and removed the old belt. However, when I go to put the new belt on, the white lines on the belt that are supposed to line up with the factory markings on the camshaft cog and the crankshaft cog do not line up precisely. Additionally the belt seems to be a little loose on the side without the tensioner pulley so it can’t be tightened with the tensioner pulley.
The white lines on the belts would appear to line up with the cog markings if I rotated the crankshaft cog one tooth clockwise, but if I did that then the lines I painted on the cogs before I removed the old belt would no longer line up. What is more important to line up? The white lines on the belt with the factory markings on the cogs? or the marks I painted on the cogs indicating their positions with respect to the block before I removed the old belt?
The factory marks are the most important. However you know the old belt was on correctly and the engine was running as it should. You also did the right thing by marking the belt before you took it off. Mark the new belt using the marks from the old belt. Install the new belt using the marks you just put on the new belt and it will be exactly the way the old one came off. And once you release the tensioner it will all line up the way it should.
Next rotate the engine a few times and check that the factory marks line up. The belt may seem off or loose until the tensioner is tightened against the belt.