Adjusting position of chainline - 3 piece BB

[horsefarmer]

What I'd like to do is transplant older Schwinn road bike 3 piece bottom bracket and crank set into a newer Schwinn mountain bike frame. When the fixed cup is tight the front sprocket rubs the chain stay slightly and chain is offset a tiny bit inboard. If I loosen the fixed cup maybe 1 turn, everything clears and lines up. I have a BB spacer, but it is too thick and I cant get the adjustable cup to take out the bearing slack then.
Can I put something on the fixed cup threads (like plumbing teflon tape) to keep the cup in place, at least so I can test ride the bike and see if I like the gearing? I also thought I could use JB Weld but would rather keep it removable so I can make changes to the bike.

 

[Bicycle808]

Whatcha want is a very slightly longer BB spindle.

 

[us56456712]

What I'd like to do is transplant older Schwinn road bike 3 piece bottom bracket and crank set into a newer Schwinn mountain bike frame. When the fixed cup is tight the front sprocket rubs the chain stay slightly and chain is offset a tiny bit inboard. If I loosen the fixed cup maybe 1 turn, everything clears and lines up. I have a BB spacer, but it is too thick and I cant get the adjustable cup to take out the bearing slack then.
Can I put something on the fixed cup threads (like plumbing teflon tape) to keep the cup in place, at least so I can test ride the bike and see if I like the gearing? I also thought I could use JB Weld but would rather keep it removable so I can make changes to the bike.

Are the axles (spindles) from the two cranks the same length? Modern, even square taper ones, tell you the axle size and I almost always need to replace the spindle with the new crank to keep it from rubbing. I don't know of any data for this for old stuff. Do both cranks have the same number of chain wheels? This could call for a longer spindle? I may have not understood your question but you might not be able to test it without the proper sized bottom bracket. I would just try it without any teflon to see if I like it. I might stay put long enough. If not, another idea is to try red Lock Tight. Torch heat will make it so you can get it apart again.

 

[horsefarmer]

The newer Schwinn Mountain bike was purchased used at a swap as a bare frame. I have a cartridge bottom bracket and a couple of spindles that are from Walmart bikes, they are all too short. This spindle came from same early 80's Schwinn road bike as the crank and is maybe 1/8" longer. The red lock tite is that the permanent type? I did not know heat could release it.

 

[us56456712]

The newer Schwinn Mountain bike was purchased used at a swap as a bare frame. I have a cartridge bottom bracket and a couple of spindles that are from Walmart bikes, they are all too short. This spindle came from same early 80's Schwinn road bike as the crank and is maybe 1/8" longer. The red lock tite is that the permanent type? I did not know heat could release it.

My car mechanic used it on my locking 4 wheel drive hubs. I had them converted so they would lock up right away instead of rolling until they locked. They kept coming loose so he used red lock tight. He had to replace one and told me that heat releases it. Check it out on the net. Perhaps the blue would be good enough. I may have released the red with my propane torch, can't remember for sure but I think I did.

 

[horsefarmer]

Frame is a Sidewinder FS - I believe it takes a 68mm 2 5/8" shell. I have a used
TruVativ Bottom Bracket - LE Square Tapered BB 03 SQ LE 112/68E but it is too short believe it's about 4 1/2 wide total width. The spindle that almost works from the older Schwinn is about 4 3/4 121 mm.
so I see I can get a
Shimano BB-UN26 Square taper Bottom Bracket in 68 x 127.5 mm size would this be a good choice?

 

[us56456712]

Frame is a Sidewinder FS - I believe it takes a 68mm 2 5/8" shell. I have a used
TruVativ Bottom Bracket - LE Square Tapered BB 03 SQ LE 112/68E but it is too short believe it's about 4 1/2 wide total width. The spindle that almost works from the older Schwinn is about 4 3/4 121 mm.
so I see I can get a
Shimano BB-UN26 Square taper Bottom Bracket in 68 x 127.5 mm size would this be a good choice?

That might be too big, or it could be OK. Trial and error might be your only option. Too bad you can't find out what the crank manufacturer recommends. 3 mm too big is OK usually. So if 121 almost works would a 122.5 be what you really need? Then 127.5 is too big as it is more than 3 mm more than you need. It could mess up your chain line. If you need a 122.5 and used a 127.5 it would move your chain 2.5 mm more outward, which is too much. I like the old asymmetric spindles, and I can't tell the difference between the two types when riding. Perhaps you could order one and send it back for an exchange? Bicycle808 recommended a slightly longer spindle. I don't remember what size spindle I put on my Giant ATX when I put on a new crank, but I had to order a longer one per the specs with the crank. The old and new cranks were both triples. I tried the original spindle but it was too short to allow it to shift to the small chain wheel even though everything cleared. Make sure that you can shift to the smallest chain wheel before deciding to keep a spindle. The front derailleur can't be adjusted far enough inboard for it to engage the smallest chain wheel if the spindle is a little too short. I hate figuring this out, trial and error seems to be standard practice with old 3 piece cranks. I like old stuff but sometimes I am tempted to take the easy way out and use some new stuff, even though the industrial design and esthetics seem soulless to me. I hate the look of a lot of that new stuff.

 

[Bicycle808]

There are a lot of different cranks, and they will all give different chainline depending on what spindle they're hung on. If you know the make/model of the crank, it is possible to find out what the oem bb spindle was, but it probably wouldn't help in this case as you're putting a road crank on a mtb frame. In many cases, this means you'll likely need to achieve a different chainline (depending on the mtb's vintage) and, in this case, you also need more clearance for the wider stays of the mtb frame. If the crankarm clears the stay but the inner sprocket doesn't, you might consider just using a smaller inner sprocket, if at all possible, and run the 121mm sprocket... the 127mm spindle would probably clear the stays, but it may end up putting your chainline pretty far outboard, which will impact shifting performance.

 

[horsefarmer]

Pics show spindle pushed out towards the fixed cup 1/8". This is complete bottom bracket and sprocket from Schwinn road bike. I have removed the inside sprocket for clearance and going to run a 1 x 6 config.

 

[horsefarmer]

Trip to LBS on Friday yielded a maybe 3/8" wider spindle. (longest one they had in their "stash".)
Kinda split the difference increasing offset on both sides, but was enough to go from interference to a 1/16" clearance at the front sprocket.

Now I know why the bike frame was at the swap for cheap, the non drive side threads were in really bad shape and could barely start the cone threads. Cleaning rust or dirt or remains of an old cone or whatever the Junk at the bottom of the threads helped a little. I cut a couple of slots lengthwise in a cone and using oil chased the threads but still very tight after maybe 5 turns in so I ground a taper on the threads of the cone about half way and got everything lubed and adjusted.

 

[deorman]

Looks like you figured it out. I was going to suggest grinding the threads out of a locking ring and sticking it on the fixed side.

 

[horsefarmer]

Looks like you figured it out. I was going to suggest grinding the threads out of a locking ring and sticking it on the fixed side.

Good idea - if I have any more problems I may try that. Only limited by the depth of threads on the non drive side cup.

 

[Bicycle808]

You wouldn't need to grind down a lockring; freewheel spacers are the right size and would fit. I predict a set-up like that would creeeeeak a lot though, unless we're just talking a mm or two.....