Shimano STX chainset replacement - help!

[davidj]

I have an old Trek 7000 MB which I've had 20 years or so, bought it from new whilst living the the US. Its 21-speed with a Shimano STX setup. It started jumping gears in lower gears so replaced rear cassette and chain.

Problem is now that the new chain is sticking to the small front chain wheel and sucking back. On closer examination I see the teeth on the smallest front chain wheel are really badly worn (very pronounced shark-fin effect).

The front chain set is 24-34-42 / 17.5 cm crank / square taper.

So I'm trying to work out my options for replacing this:

a) Replace just the smallest chain wheel. Google suggests there is zero chance of getting this part now - or am I looking in the wrong place?

b) Replace with a cheapo 24-34-42 chain set off eBay - e.g. in the £25 range. These say they are "SIS compatible" - will one of these work? They also seem to be 17 rather than 17.5 cm cranks - does this matter?

c) Replace with something better. I've no idea where to start here. The more expensive ones (e.g. SLX) say they are 10-speed compatible - will this be a problem as my bike is 7 speed? I don't really want to replace the bottom bracket for octo-what-ever-its-called either.

d) Buy a second-hand STX chain set of eBay. Have seen a couple of these - they seem to go for ~£30 - but if the pictures are anything to go by they don't look a whole lot better than the one I've got.

e) Don't use the smallest front chain wheel ... not really option as we live on top of a very steep hill and I'm pushing mid-50's .

All help / advice gratefully received.

Thanks,
Dave

 

[Smurfy]

a) Replace just the smallest chain wheel. Google suggests there is zero chance of getting this part now - or am I looking in the wrong place?

If it's bolted rather than riveted, then there's a fair chance you can replace the small chainring (post a picture up if you don't know what to look for).

First of all, use this cribsheet to find out what BCD you have (bolt to neighbouring bolt is much easier to measure than BCD)

Next, have a look at these spares, and see if you can find one with matching BCD and number of teeth.

 

[davidj]

Thanks. Looking in more detail then I found that I have the first generation STC chain set which uses non-standard chain rings. However I got really luck and found the part I needed to replace on a German bike parts website - last one in stock. Got it delivered for about £20 and all now good!

 

[milosilija]

Hi can youl write me link and whuch chain rinbg you bougth for stx. I have the same problem. Which chain did you buy? thanks