GMC Cycling - Recent Questions, Troubleshooting & Support

Can you explain why you think the tires are too big? Do they NOT fit the rims? What condition was this bike in when you bought it? If the brake pads line up with the rims then the wheels are correctly sized for the frame.

If the wheel has nuts (not bolts) on each side you just need to loosen each one enough to remove the wheel. I’m happy to help further over the phone at https://www.6ya.com/expert/donald_f2ed37026a3ac881

700c tyres are bigger than 26".The tubes you need measure 700x28 (to32).This size is used in Hybrid style bikes.Make sure you get the same type of valve(Schreader are the same as car,Presta are narrower)or it won't fit the hole in your rim.
Make sure when inflating that the tube isn't trapped between the tyre and the rim.Only inflate to the pressure written on the sidewall of the tyre.

I have the same bike, I believe the correct Bottom Bracket size is 68mm x 122.5, if you use a Shimano BB-UN300 which is also compatible with the BB-UN55/54 sizes. There are many Chinese knock offs for a few dollars less, but not worth the risk of premature failure.On a side note, if you measure the length of the stock spindle it’s about 124mm which Shimano does not make.

Bottom bracket is possibly shot.

http://www.parktool.com/blog/repair-help/trouble-shooting-a-creaky-or-noisy-drive-train

http://www.parktool.com/blog/repair-help/categories/bottom-brackets

A real Bicycle Sop will have all the special tools and skill necessary to repair it.

Repainting via rattle-can is a bad idea - looks poor and will not hold up. As for forks, just google "overhaul threadless headset." I’m happy to help further over the phone at https://www.6ya.com/expert/donald_f2ed37026a3ac881

Serial numbers are generally found under the crank, stamped into the case.

Remove the bolt and put a lock washer between the bolt and head. That or put some blue loctite on the threads. Just remember to have the head removed from the fork tube before the bolt comes out or the expander will come off in the forks.

Sounds like the braze ons, that's what they're called, are broken in the frame. Only thing left is to drill them out and replace them with Rivnuts. Your local bike shop should be able to handle that.