Timing Chain

[jgbailey57]

I checked my timing last night trying to find a knock my engine has. The tensioner is almost all the way out so I know the chain is stretched which means the cam is retarded. Could it be retarded enough that the exhaust valves are hitting the piston causing the knock? The front timing mark is maybe 1/8" above where it should be. This is on a 400ex by the way.