The tensioner is a one way ratchet that will only move in the direction that tightens the chain. When the head was removed it went to the full tight position, leaving it this way will tear up the chain and gears.

The large nut on the tensioner must be removed, it is under quite a bit of spring tension be careful, then the plunger removed toward the chain. Upon reassembly after the head is installed the plunger gets put in from the outside, the spring and nut then get reinstalled.

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