Crankset on an old MTB

[ElyDave]

I have an old 7-sp MTB, and was looking at the crankset while waiting for a train the other day.  Starting to look a bit ragged, so I was thinking about replacing the chain rings.

It's square taper, which I think I can handle (just another version of removing a flywheel), but it looks like the chainrings are all welded to each other and the RHS crank. 

Does thank mean I have to replace the lot?  I'm assuming square taper cranks remain available, as do 7-sp cassettes?

TIA

[Brucey]

yup, if all the chainrings are joined together, you will need a new crankset. There are a fair number to choose from. However unless you are careful (or lucky) you will need a new bottom bracket too, because there is no standard length arrangement.

BTW if you want the shifting to be as good as possible, it is a good idea to stick with the original chainring sizes.

cheers

[ElyDave]

cheers,

so how do I decide which BB?  As you say there are a multitude of square taper ones available. 

Had planned on keeping similar chain rings, not looking to gear it up at all as I prefer a higher cadence.

[Torslanda]

At least a couple of the low end Shimano square taper sets use a 123mm BB. I stock a couple of sizes FC-M171 28-38-48 and FC-M131 22-32-42, very much at the cheap'n'cheerful end of the market. If you want something prettier See what Spa Cycles have to offer. There's a couple of bargains there. Spa will of course tell you what length BB you will need.

Work well with 6/7/8 speed systems. As Brucey said, change like for like, it avoids having to bugger about with the front mech. 7 speed cassettes should be readily available from your LBS. Don't skimp on the chain quality.

[ElyDave]

I like that last bit, the chain is twenty years old and has never been cleaned or given even a hint of lubrication 

[SoreTween]

I'm in a similar position, I'm collecting parts to refurb my ancient mtb also mostly due to the chain rings.  After having owned the thing something over 15 years I spotted that the chainset model is stamped on the inside of the cranks in an arc around the pedal hole (Shimano). Astonishingly I then got a bnib matching set off eBay. There are also brand new old parts listed from dismantled unsold stock. Might be worth checking your cranks.
The closest looking modern crank set has just stopped being listed by the usual suspects. When one of those turns up on ebay I shall compare the offsets, see if the modern one would work.