If I swap out the crankset on a stock Trek 520 for lower gears like a Lx 46/36/24, what else will I have to modify or change. (front derailleur ... rear...).
Will LBSs do it for free or minimal charge? What is high end cost vs. low end?

Thanks for the help.
Rob

My LBS switched out the crank to an LX for no charge and no change to BB, derailers, or shifters. Might have to shorten the chain.

Worked fine.

EDIT: Let me retract the statement about the BB. I recall now that they did something with the BB, but still no charge.

I asked the same question here but I can't find it. It was about swapping for a 22-32-44. The answers were that the bottom bracket had to be changed also. Derailleur was not a problem. I'm sure others will chime in.

As for cost, your LBS will know better than us! I asked a LBS, he didn't want to do it at first and tried to convince me that I didn't need such low gears but seeing I wouldn't let go, he finally said he would credit me for the parts and do the job for free (since it's a new bike).

bradw, you didn't have to change the BB?

I modified my original statement. Something was done with the BB, maybe an entirely new one. But they didn't charge for it.

you have to swap out the bottom bracket if you use a LX crankset. The spindle won't be long enough if you use the 105. I swapped mine out myself it worked great on my last tour.

The stock saddle will have to go too.

Two possibilities:
- Keep the "105" crankset and go for 48-38-24.
You can't go lower than a 24 granny and a 38 middle ring.
Obviously, no need to change the bottom bracket.

- Get an LX or XT crankset with 44-34-22. I know the XT crankset needs a different bottom bracket than the 105, but I don't know about the LX.

- Derailleur issues.
None, as long as you use the bar-end shifters. You will have to slide down the derailleur a little bit, so it is closer to the rings.
If you go with STI, some people recommend to grind the outer cage, especially if you choose the LX option.