likebike23

My take on big box bikes is that extremely poor assembly followed by lack of maintenance is the cause of much of the premature wear. If I could only afford a big box bike I would invest some time tensioning the wheels and re packing the hubs. The headset and bottom bracket (unless it's a cartridge) should also be repacked. These items are under lubricated and over tightened from the factory in my experience.

I like the Sun Race friction thumbie idea, but only after the original shifters broke. The brakes on these bikes are terrible also, I've had fits trying to get them to stay in adjustment on the neighborhood kid's bikes. The cheapest Shimano Canti or V brakes would be a huge upgrade.

If you are going to stick with these bikes, they will require more maintenance than a better quality bike will. If you are up to the task fine, but I wouldn't pay a shop. Another thing you could do would be to look for inexpensive rigid mountain bikes from the 80's or 90's that were expensive when new. Lots of times you can pick them up for $50 in my area.