TA Crankset Help
 

I have an old TA crankset 170 arms in good shape - it is set up as a triple 54-40-28. Blasphemy or not I want to put it on my 2011 Soma touring bike set up as a double 44 - 28 double with modern chainrings. I also want to get a sealed bottome bracket. I figure you vintage guys are the best to handle my questions.

So questions
1. Can triple to double be done? How?
2. What bottom bracket do I need?
3. Is Rene Hearse out of Colorado the best place to get modern rings?
4. Is there an outer ring chain guard that doesn't cost a fortune? (which makes it a triple).

Thanks ahead of time for your help!

1. Yes. You need a 44t OUTER ring and hardware for two chainrings. You will reuse the existing crank-to-outer ring mounting bolts. If your 28t ring is in good condition just keep it as the new TA rings won't offer any practical advantages.
2. 115-118 if you're going to use a JIS symmetric spindle. I recommend buying a spacer or two while you're at it.
3. I think they may be. There are a couple of European vendors with reasonable shipping too.
4. Not sure.

If you are going to use 10sp or greater, I would consider a Velo Orange ring in the outer position as it will improve shifting. I think they're only available in 46, 48 and 50t sizes, though.

Velo Orange and Electra also have chain rings that fit, though probably not the size you want. If you want an outer ring chain guard, and are willing to consider the blasphemous option, you could just file the teeth off your existing outer ring. Change your middle ring to a 44T; I don't think there would be any advantage to changing the inner ring.

I think Justin nailed points 1-3 on the head.

Just a couple of comments I'll add-- if you decide to file the teeth off your existing 54T outer ring to create a chain guard, then you won't have to purchase new double-chainring bolts, which might otherwise set you back $20-30 (I haven't checked prices recently). Also, keeping a pseudo triple/chainguard setup, you will only need to buy one 44T inner ring, which is cheaper than buying a new outer ring with the same number of teeth. So converting the outer ring to a chain guard can potentially save you some money, or at least offset the cost of having a machine shop do it for you.

Also, if you stick with double ring + chain guard (triple), you will need a longer spindle. Figure around a 122mm. I have several TA crank setups, and the one I have closest to what you are proposing is a 46/26T double. For that I'm using a 115mm JIS spindle and a 1.5mm spacer on the driveside. That leaves me with just about 2mm of clearance between the inner chainring teeth and the chainstay. Close, but that's how I like it.

Lastly, since the Q factor of the TA cranks is so low, if you are running a 10-speed cassette, you may get interference between the chain and the tip of the drive-side crank arm as the arm rotates past the chain when in the smallest cog. This will most likely occur if you run a double configuration on a 115mm spindle, but if you go with a 122mm spindle / triple setup, you should not have this problem. With my TA double on 115mm spindle, the chain just clears the crank arm by about 2mm when on the smallest cog of an 8-speed cassette. Rear spacing is 130mm.

Interesting info right here.

Looking at the prices of TA rings and bottom brackets - how much is TA crankset worth with 54-40-28 plus bb in good shape?

I have 135mm spaced frame and am running a 46/30 w 10 speed rear. I am using a 124mmbb w/ 2 spacers.

I'll give you a Jackson. :D

Good to know... so basically a TA crank is compatible with just about any rear cluster/spacing as long as the BB is long enough. I suspected as much, given basic math, but it's cool to have this verified. How wide are your spacers, and what did you do about the left compression "cup" since the BB is moved so far toward the drive side?

Spacers equal 3mm. So total would be 127mm. Had no issues w/the cups so I am not sure what you mean. FWIW, I used a VO cartridge BB. One problem I did have, was that the 10speed chain, being so much thinner than 6 speed chain ( I was using early 80's Sugino rings 46/30) would get caught between the rings. I got VO 46, ramped outer and now have no problems.

What I meant was that low-end and mid-level Shimano non-drive side cups (the plastic ones) are flanged and don't thread in past where the flange meets the BB shell. When you space the BB toward the drive side using spacers, the plastic NDS cup needs to thread in further to provide adequate compression around the cartridge. The only way to do this is to file off the flanged section of the cup. Higher end BBs with metal NDS cups don't have that flange, and can be threaded in as far as they need to be. Sounds like the VO NDS cup is metal so it doesn't have this problem.