So I've just done up this nice '90s Trek 750 that has its original SLX (FC-MC32) triple chainset on it. I'd really like to keep the cranks, but two of the chainrings are badly damaged. Should be as simple as changing the rings but they've got a weird setup where the middle ring has its own attached spider to which the outer ring is bolted – I don't think I'm gunna be finding a like for like replacement in a hurry. So what would you do? 1x not an option for the bike's purpose (touring bike for my partner), but the original rings (42-32-22) seem like a loooot of range to me so would be happy for it to become a 42-32 ish double if necessary, but can't work out how I'd even do that! Thanks.
by djuna_moon
5 Comments
yeah, i’d make a 2x out of it. It will be hard to find larger than 32T chainrings for BCD74 though.
There are so called “tripelizer” chainrings out there from ta specialite, stronglight and also some bmx shops. Those usually have BCD130 or 110 holes and BCD74 threads. There is a bassi triple chainring that would work, but priced at 80$. If you drill away the threads in a drillpress to make room for classic chain bolts, that could be a solution. You need the right spacers and the chainline would change a bit.
Considering you can get a Sugino XD clone or even a used Campy Euclid triple for the price of those special chainrings, i think it it casting pearls before swine on an STX. Just get an appropriate DX or XT Chainset of the time with classic BCD110 spider and it will look almost identical and cost half that.
What type of damage are we talking about? Is it wear or just bent?
If bent just try to readjust it with plyers.
Finding like for like replacement is nearly impossible, as it was the only crankset (that i know of) that was setup this way.
The teeth look OK in the pics. Those had some wild ramps that look like the chainrings are “torn” so if you’re seeing that, it’s normal.
Unfortunately, you’re mostly out of luck. Off the top of my head, those were 67 BCD. No one makes those rings that I know of. Your only hope is Ebay or a bike collective if you ask me. Wish I had better news.
Those are shift assist features built into the rings. The cuts and hollows grab the outer links of the chain during upshifts to the bigger ring, and the short teeth on the rings are gates through which the chain will drop to the smaller ring on downshifts.
This misconception about shimano “hyper” style rings being worn out or damaged are common among people who are not familiar with their intent. And those steel rings might be heavy, but they’re bombproof. Clean that crank and ride it!