bike_galpal

i have my bike set up as a 3x1 right now. i finally got it working fairly well with some parts bin stuff, except for the chain tensioner. i had mismatched crankarms for a while, then i got a 122 bottom bracket to fit all the gears on my Tourney XT triple (idk anything about these cranks, but like them!!)

on getting my chainline correct (i think) i found that my front derailleur was pretty hecked up. and i think independent of that problem, it wasn't shifting into my littlest ring. this is all friction shifting.

now that i've had it working and i know how much i like it (it's a lot btw) i'm trying to decide if i want to get some external BB cranks, probably just deore. one of my questions is, will a 2 piece external bearing crankset potentially cause me any extra problems with setup, chainline, front derailleur etc? or will it wind up being easier?

rear is staying the same for now. my main concern is that as things are, no front derailleur will pull the chain far enough in to shift to my granny/hill gear. i'm not really sure if this is true or not, and i realize a shift down from a compact 34t chainring isn't the best. but can someone help me identify the features i need in a front derailleur, and what extra setup i need to do? and if a more modern crankset would make this way easier, just say the word...

i've been using a top pull with a cable stop on my seat tube, but i'd use a bottom pull if it's possible (???) an extra factor however is that the front derailleur can cut down on my rear tire clearance, and i'd like to stick with a 32c.

also if anyone is curious, my gearing is 42-34-26 x 13 right now, but i'm really liking the sound of 42-32-24 x 12. my rear wheel was a 130mm spaced 9 speed, i spaced it down to 120mm ish by removing the cassette lockring and using the right sized seatpost clamp to keep my rear cog on.

maddog34

you may need a 127.5mm spindle BB.

how does the gap between the crank tips and chain stays look? Even? uneven? really close on both sides?

and get a better set-up on that freehub, bub.

spacers, cog, spacers, retainer ring. doing that correctly will help sort out your chain line, AFTER you sort out the front line.

you can rob some freehub cog spacers out of an old, trashed cassette, eh?

70sSanO

If I understand your 3x1 correctly, you have an 80's Takagi Tourney XT triple crank to a single 13t cog in the back. Your first step is to measure the chainline (google Sheldon Brown chainline) that is a measurement from the center of the seat tube to the middle cog. That will let you know if your spindle is too short. For mountain bike cranks, it is around 47.5mm (47.5-50). If it is road, it is 45mm, but the quick research I did has the Tourney crank as a touring crank.

As for your front derailleur problem, if your chainline is less than it should be (too short a spindle) you will have a problem and need a longer spindle. You can get bottom pull mountain bike front derailleurs. An older Shimano XT 737 might be a good choice for your setup.

John

Edit added: Yes a bottom pull will cut down on your tire width, especially with a mountain bike front derailleur. Also, the wider the bb spindle the more interference you would get because the cable attach arm will be pulled in more for the large chainring so top pull might be better. You can cheat a little on the chainline if you get a front derailleur for a larger diameter seat tube and offset the shims to bring it closer. I have also taken a file out judiciously to get a derailleur ever so slightly more travel when I just need a little bit.

bike_galpal

thank you!! what about the crankset, will that cause me any extra problems? i've heard chainline adjustment can have a few more limitations?

also unfortunately that front derailleur will still not clear my rear tire.

ahh ok, thats a really good tip, thanks! would it also increase the travel a little if i were to use a braze on adapter and direct mount derailleur?

ThermionicScott 

Be advised that a 12T cog will wear out really fast and run rough if that's what you put all your miles into. There just aren't a lot of teeth to share the load and the chain has to articulate at a tighter angle to go around it. If it were my bike, I'd try to go in the opposite direction so I wouldn't have to replace chains and cogs all the time.

70sSanO

Let me first say that chainline should be adjusted for seat tube diameter to begin with. In theory the distance from the derailleur cage to the edge of the seat tube is the same. The chainline needs to be adjusted to compensate for a larger or smaller seat tube diameter. What this means is working the shims won't help if your chainline is way off, so I wouldn't buy a 34.6mm clamp and expect working the shims to fix the wrong spindle. But if you already have a 34.6mm and need to bring it in a fraction of a mm, working the shims has worked for me.

As for a braze-on, I don't think you can manipulate it enough laterally(?), in and out so to speak. Your issue is the seat tube.

I still think you need to address the spindle width to give you the right chainline and go from there. The only other reason you can't shift to the small chainring would be if your 13t is in the normal small position, and not centered on the freehub, because the angle is too severe. Same effect if you are running middle ring to small cog and want to shift to the small chainring.

John