I have a cheap ($100) 26" Walmart mountain bike (Hyper Summit) that has a triple chainring (24,34,42). It appears there is no easy way to remove the granny gear since it has what looks like some type of rivets. However, the BCD (Bolt Circle Diameter) appears to be 58mm which is a standard size. I would like to go with a 20 granny chainring cuz I like to ride thru tall grass and need a lower gear. My rear gears are a 7 speed freewheel with a 28 as the largest cog so currently, 24/28 is my lowest gear which is about 22 gear inches (26" tires). I will eventually be changing to a 34 largest rear cog (Shimano MegaRange 7 speed freewheel) but I also want the change the front granny chainring for a double gear reduction which I know I will like. So any ideas how to get the granny gear off? It connects in 5 places (starfish pattern). My goal for my lowest gear is 20/34 which will give me about 15 gear inches.
I was thinking if I can somehow get those rivets out without damaging anything critical, I can probably use some washers and chainring bolts to handle any difference in hole sizes. It seems like it can work with just some light machining. Once the chainring is off I can have a bike mechanic work on it. There is always a brute force method too. For example, cutting the teeth off of the 24 chainring and attaching the 20 chainring to it. However I prefer trying to bust out the rivets first as the BCD of 58mm matches up with available 20T chainrings.
UPDATE: I am moving forward on this project so will update when I get some actual results. It might take a month or so to get the parts and schedule a bike shop appointment. I think at minimum I should be able to get the different freewheel gearset installed but not sure about the 4 tooth smaller granny gear. If I can get both it should be awesome cuz that will then be a low gear with 15 gear inches which is very low.