I rode a cheap heavy steel mountain bike at 26 stone, the first thing that went was the bearings in the front wheel and I had to true the 26" wheels more than once when I hit pot-holes. I lost weight rapidly but after riding perhaps a couple thousand miles in total which by then I was maybe 18-19 stone I replaced the caged bearings of the bottom bracket with new loose bearings and fresh marine grease. The bearings were only about a £1 delivered (probably ebay). The bottom bracket was as good as new. It can be a bit finicky adjusting the bottom bracket for no play. Pretty sure I rode it for about a week and then had to adjust it again but that second time lasted a very long time. I could of gone with a sealed bottom bracket but I really didn't need to, the original only needed fresh bearings and grease and it spinned much better with loose ball-bearings. I'm just making the point you probably could have bought it back to good working condition spending even less money. There are millions of bikes all over Africa getting huge abuse and being massively over-loaded and they don't have fancy sealed bottom brackets etc that wouldn't be cost effective to them.