I replaced the timing belt on a my 2003 Honda Accord V6. Before removing the belt, the crank was at TDC and the camshaft marks were aligned properly. In reinstalling the timing belt, I was very careful to not disturb the camshafts or the crank, and verified their original positions. (However, I did NOT manually turn the engine several rotations.) The timing belt went on correctly, and the tensioner held everything tightly. Once reassembled, the engine started but ran VERY rough. I thought I had a bad spark plug connection, but all checked out. When trying to restart... nothing. So I tore everything down again. When the crank was set to TDC, the camshafts were several teeth off the mark! What happened? Can the camshafts be safely turned to realign the marks with the crank at TDC? Any recommendations would be appreciated!

You can set the crank to TDC with the belt on, then you take the belt loose and set the cams to same. IF you do it the other way you might have a problem.

Thanks. I did set the crank first before removing the belt. I tried moving the camshafts, however, they seemed difficult to move and I did not want to force it. Is this normal?

In the future, it's best to place a mark (e.g. Whiteout or white paint) on each pulley and corresponding point on the side of the old timing belt, before removing. Then, remove old belt, transfer marks exactly to new belt, and reinstall with confidence.

Was the engine set to TDC on the compression stroke?

Yes. It was set on the compression stroke.