It's actually pretty straight forward to moving parts from one bike to another and actually a fun and "beginner-worthy" project for the most part. As mentioned, a couple of issues may be the fork and front derailleur. But neither are difficult to deal with, but may cost some money (or not). The other parts should go right over, with only the bottom bracket/crank requiring any special tools other than normal bike maintenance/adjustment tools (wrenches, allen keys, etc.). When you get to moving the BB/crank from old to new, sometimes it's cheapest and easiest just to farm that part out to a shop. The rest of the parts can be moved over and adjusted pretty easily if you're willing to read up on the parts you're not familair with (a good repair manual or one of many good websites).
For the fork, I don't know the Trek lines, and it may be a given that they all use the same type of fork. But potentially, there is a little more to it than just the steer tube length you need to verify.
First and foremost: does not that new frame come with a fork? They usually do and really, this is the way to go and you should just use it. Forks are designed for the geometry and usage of the bike (road vs. touring vs. cross, etc.). Again, the old fork may be perfect, but you need to verify all of the following to make sure:
Steer tube diameter. They are probably 1 1/8", but you should check.
The two frames' headset type may be different, but that's not an issue with the fork itseslf. You might have to get a new headset if the new frame doesn't come with one, and it's different than the old one, but they're relatively cheap ($25-$50). If your new frame comes with a fork, it will also have a headset.
Brake type: normal road caliper brakes, vs MTB type brakes, vs disk brakes.
Then you need to know if the "rake" and "crown to axle length" (length of the legs) is the same or close. You could simply contact Trek and ask about the fork geometry of either frame. While frames usually come with forks designed for them, there are generic forks and people switch out forks all the time (I did). If they are significantly different, you probably need to buy the new frame with a fork or find an after market one that's similar. I do believe, if your Madone fork is not damaged, you'll be able to get a good price for it on ebay. OEM forks seem to be in demand, especially if the buyer's looking for a particular paint job.
If rake and leg length are OK, then you need to know of the steer tube on the old fork is long enough to give you enough length for the fit you want on the new frame. Basically, what you need to know is the total length of the steer tube from the crown to the top of the stem clamp. Then, look at the head tube length of the new frame and decide if that length will give you enough steer tube above the new frame's head tube to give you the stem height you want on the new frame. Does that make sense?
But again, the simplest is just to use the fork and headset that come with any particular frame, or get an aftermarket fork specifically for that frame, especially if you're not familiar with this stuff and aren't interested in getting too involved in the minutiae (some of us are, some not).
As for the front derailleur - your current derailleur which works on your current frame may or may not work on the new frame or may need to be adapted. But this won't be a big deal at all regardless.
First, what is the attachment type on the frames? (clamp or braze-on).
If both are braze on, you're good to go.
If one is clamp and the other braze, some derailleurs easily adapt from braze to clamp or vice versa by simply attaching or removing the clamp. (My Ultegra for example).
Second, if clamp-on for both, what is the seat tube diameter (which determines the clamp size, if clamp) on both frames?
If they're the same, you're good to go.
If not the same, some derailleurs easily adapt to different clamp size (for different seat tube diameter) by simply changing the clamp.
Worst case: you buy a new derailleur which depending on the group level, could be pretty cheap, especially if you can find a good used one on ebay, after which you sell your old one on ebay for a very small net cost.
Thank you for Camilo for the info, as of now I have decided to leave my parts swapping idea alone and concentrate on learning how to ride my new Trek 2.3, and after a suitable period of time I'll probably start to build myself a "Dream Bike", until then I'll just leave the 7.1FX as is.
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