No 15 mm nut
Thanks for the reply. Unfortunately there is no nut in the center of the tentioner pully. I see three things that I think are related. 1) a 13mm long nut that sticks out about three inches and is located near the water pump. 2) a 13mm nut that's located between a couple of pullys and 3) a large allen nut in approximately the same location. I' ve loosened both the top nut and the one by the pullys but it's had no effect on the tention of the belt. I've attempted to loosen the allen nut (I think it's 10mm) but it won't loosen easially and I'm afraid of stripping it if I ream on it. It already feels soft. That's where I am so far. I hope this will ring some bells for you because this is just phase 1 for me in my quest to change out the water pump.