The tensioner rod (the reverse-thread one) may not be seated on te rear of the tensioner body correctly, not allowing it to seat up against the engine properly. The little bracket on the bottom end can be mounted two ways, right and wrong. Ask me how I know.The big bolt is right-hand threaded.

DG

244brick, did you only loosen the 19mm bolt a few turns, or did you completely remove it? If you completely removed it there is a chance it's misaligned with the threaded hole. Use a drift pin to align the tensioner with the hole, and try again. If you only loosened the bolt a few turns then the threads must be stripped.

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Fred Hoelzle