Take the tensioner push rod hole cap bolt off. This is a bolt facing towards the bottom of the engine, on the upper engine case front, above the tensioner lock bolt. Loosen the tensioner lock bolt. Poke something long and thing down the hole beneath the cap bolt, to touch the end of the tensioner push rod - nail, cut-off coat hanger, thin screwdriver, whatever. Now turn the crankshaft backwards a bit while lightly pressing down on your whatever. If everything is free the rod moves a bit upwards when you turn the crank backwards, and down again if you then turn it forwards. This is the tensioner blade on the rearward chain run between crank and cam flexing flatter under the chain tension from turning the cam backwards... when it flattens out it gets longer, pushing the rearward end of the "horseshoe" down and eventually the push rod upwards. Turn it forward and the tension is on the front chain run, leaving the rear tensioner run slack again.
If there's no movement in the push rod as you do this then the tensioner mechanism is likely stuck. The push rod may be stuck in it's bore or the horseshoe pivot may be damaged.
