I pulled this engine apart and in the process of re-assembly, trying to get it running by tonight. The round dot on the sprocket is either 1/2 tooth above or if adjusted again, 1/2 tooth below the mark on the casing. I'm the 2nd owner, and to my knowledge, the head has never been machined, chain is tight. What should I do here? 1/2 tooth makes a huge difference on the crank timing mark alignment.