Murray Missile 

I acquired a couple clapped out TREK mountain bikes from a co-worker, one is pretty much parts only but the other might be made road worthy again. It's about a 2005 820 and it's only "major" mechanical issue is the fork, it actually feels good but the right lower leg has a sheet metal sleeve sticking out of it about 2 inches. Is this a liner to protect the inside of the aluminum leg? If so, is it a big deal to put it back into position with the fork disassembled and once in position what keeps it there? I don't have much in this bike but I also don't want to put much into it beyond consumables so a fork replacement really isn't part of the plan, I can part it out and easily double my money, probably triple it but it's all easy and cheap stuff if I can fix the fork easily. I have no reservations about a fork disassembly, clean and reassembly. The other TREK is a 2014 Cali 29 inch disc brake women's MTB missing the front wheel and brake rotor and the RD is mangled almost beyond recognition, the fork on it is good but unfortunately it won't work on the 820.