87 250X timing and other questions

[blacknblue#2]

I am workin on a 250X for a buddy. When i took the side case off of it i realized the timing chain had some off the bottom gear. The tensioner is still good so what the world could have caused this????? and also i see it only has one timing mark on the cam gear. Im guessing it lines up level with the top of the head but just to make sure im right is that correct. I know hoe to get an engine in time just a lil confused with just the one timing mark......thanks alot guys

[dork]

worn chain and or guides. also re check the tensioner by extending it out and try to push in on it. it shouldn't push in.

the sprocket should have 2 marks; w/piston at tdc install cam w/lobes down and the 2 marks line up with the top surface of the head.