Fan Hitting Shroud

[otterby]

I have an '85 K2500. The original engine was a 454 but was replaced with a crate 502 quite a while ago. Over the past few years I've heard the fan hit the shroud occasionally but it stopped after a while. I could see where the fan was close to the left side of the shroud and had touched and there was a good gap on the right side. Now all the sudden the fan is hitting the shroud on the left side almost constantly and makes a lot of noise, but not always. Everything looks good, tight and straight. The motor mounts look good and I really don't see where there is any way to adjust the shroud the the left to center it on the fan. Something is obviously out of whack but I just can't figure out where. Any ideas?