APB engine

Changing the cam chain tensioner gasket & all seals.

On the RH side, I mark the chain and sprocket and have a problem aligning them back on assembly. I rotate the cam that was not aligned back to the correct position.

On the LH side I did not completely remove the camshafts, I slip the gasket & seal under. To my surprise, the mark on the intake side is now way off and I cannot get it to line up. I should mention that the chain is really tight when you are putting the cams back in

I am stuck. If I didn't allow the chain to slip tooth, why is it not lining up. Could it be the expansion and contraction of the tension-er that's causing the problem. The only way I see this is if the top and bottom of the tension-er expands independently thus pushing either the top or bottom out further.

Why do the chain tighten up even thou it was slack when removed?

What can I do to get them aligned again?