I came back from a ride today and noticed that my driveside crank had nearly fallen off the bb spindle . This is the second time this has happened in recent memory, and a few times in between, i noticed it was slightly lose. Any ideas what's causing this or any possible remedies? Cranks are 75's, bb is iro.

when my crank did that, it turned out it was rounded out. take it off and check to see if that happened.

Tighten it back up, my guess is that you've already ****ed your cranks. If this is the case, tighten and go ride it. If it comes back loose again, time for new ones.

sounds like they weren't installed properly and teh taper got deformed.

I think s75's are ISO taper, and the IRO bb is JIS- but I'm not sure about this.

Yeah, I guess I just don't understand what I could have done to improperly install them. The taper still appears square upon visual inspection, and Sheldon says he runs jis on iso and vice versa. I'm sure i ****ed **** up somehow. blah

this happened to me once after I painted my bike and put it all back together. I took it to a shop and they said that I probably had just not tightened it enough and he tightened it down to proper torque specs and I never had another problem with it.

Sounds like you ruined some good cranks..

kinda offtopic here, but did anyone else chuckle when they read "cranks are 75's, bb is iro"?

Are you using self-extracting BB bolts? The only time I had a problem with cranks coming loose was when I was using those - being paranoid about messing up a pair of nice cranks, I didn't tighten the hex bolt enough and they came off in the middle of an alleycat (whoops). And it's typically the non-drive side that works itself loose. And actually, I think the only way that you can deform the cranks is by overtightening them (since you're pushing the crank beyond the taper on the spindle and smushing the aluminum), so if you got them new and didn't tighten them enough, you're probably fine.