Gear advice please

[jimbojambo]

After stripping down my bike I have found that the front's have some teeth missing and the rear cassett is quite rusty... The bike is a 21sp and what i would really like to know is can i just buy any 7 sp rear cassette to replace it or are they specific? And also same question for the front's? Ive never rebuilt a bike before so sorry about the novice questions

 

[legrandefromage]

Chainrings with specially shaped teeth to aid shifting are often mistaken for 'missing teeth'. Unless the teeth look like shark fins (extremely worn) they may not actually need replacing.

knackered!

profiled shifting teeth/ ramps:

as for the rear cassette, if the chain doesnt skip or jump under load, the rust is not a problem and will disappear as the bike is used.

Make sure that it is a cassette and not a freewheel:

Cheap 7spd:

http://www.ebay.co.uk/itm/SHIMANO-ALVIO ... 484652a4b8

 

[jimbojambo]

Thanks, I had no idea lol looking at what you that i think they just need using then