There is a trick to this seemingly simple tensioner-the "chamfered" end of the piston (which slides freely in the bore) is actually a piston within a piston. You have to smach it with a hammer to have it pop out.I am learning this as I go, as I had a garage replace the timing chain and tensioner, but they omitted this important step.The back of the outer piston has a ball check valve. I believe it would be a good idea to bathe the unit in oil when you do it,so that the inner piston hydralically "locks" outward.