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Old 04-13-11, 10:22 PM   #1
RobE30 
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TA crank arm compatibility

As my collection of parts grows, so do my questions. I have a Campy NR bottom bracket that I'd like to pair with a set of TA Cyclotourist cranks. I also have a TA bb that I pirated from a 73 Competition that came w/ the 3 pin TA cranks. Can I use the Campy bb or must I use the TA bb?
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Old 04-14-11, 12:02 AM   #2
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You can read a lot about compatibility of tapers between diiferent standards (ISO & JIS) and how different manufacturers adhered to different standards in different years. But the best thing to do, since you have the parts in your hand, is to test-fit them. TA cranks will egage with Campy spindles since the angle of the taper is the same -- the only issue is how far on the crank will drive. An old crank, where the square hole may have enlarged a little from numerous on-offs over the years, may drive farther onto any given spindle, even it's "own", than the spec sheets say (if you can even find them.) There are two constraints: depth of crank engagement and chainline, with the first being more important mechanically.

Test 1: Take a crank and gently press it by hand onto the uninstalled spindle. Check how close the end of the spindle comes to the top of the hole in the crank. Remember that if you were to drive the crank on with its fixing bolt it would press in another 2 mm or so and the bolt at that point must not come in contact with the spindle or it won't stay tight. If you can see 3 mm then it's worth a try on the bike. If you see a lot more than 5 you might not be able to get the crank to drive on far enough for a good solid fit. If you really want to be sure, you can tighten the crank down a little to get a better estimate but we don't like to do a lot of unnecessary on-offs on these old cranks -- they don't have all that many cycles left.

Test 2: Install the bottom bracket in the bike, with balls in cages, without grease, just so there is less mess at this test-fitting stage. Campy NR bracket cups are thicker than anyone else's and can be used only with their spindles, so that means you have to install the Campy fixed cup for this test but don't torque it down yet, just screw it all the way in by hand. Press the right-side crank onto the spindle, again by hand at this point. Visualize how the chainrings would lie if pressed in an extra 2 or 3 mm and assess what that will mean for your chainline. If the inner chain ring would be 3 mm from the chainstay with the crank pressed home, you're probably OK. If it's a lot farther than that, your chainline will be be biased in favour of using small chainring with the outer cogs: you will get more cross-chaining with the big-big combinations but this is not necessarily a deal breaker since you already know from Test 1 that you have adequate engagement depth of the crank on the spindle.

If it's any closer than 2-3 mm you're likely to run into trouble peculiar to TA cranks even if the chainrings (or the end of the crank arm) don't actually hit the chainstay:

Caution: Those 5-pin TA Cyclotouriste cranks lie very close to their chainrings -- they are notorious for jamming chains in an over-shift off the front chainring -- and are intolerant of less-than-ideal chainline. If the crank sits even a mm or two too far inboard the crank arm will hit the front derailleur cage when it is run out far enough not to rub on the chain in the outer-chainring->smallest cog combination. This is even using a vintage flat-face FD like a Campy NR that is period-correct for a TA crank. I have an old Cyclotouriste that gives me this problem even on a TA spindle. To make it perfect I had to use a Stronglight spindle that was just ever such a little bit longer. I think this is because I'm using it on a bike with a 130-mm rear dropout spacing which "splays" the chain out a little farther from the centreline when it's on the small cog. These cranks date from 120 or 126mm of yesteryear, remember. (TA also made a "373" spindle that was intermediate in length between the standard double 344 and the triple 374, but my 373 is too long.)

If everything seems OK, install it for real, with grease in the BB and torque down the crank. Then remove the fixing bolt to make sure the spindle has not become flush with the top of the crank hole, then reinstall the bolt and retention cap. Finally set up the front derailleur and run it through the gear combinations. You will need to get it perfectly aligned, outer face parallel with the chainring and the limit screw not a half-mm too far outboard.

If your test ride works, you deserve every satisfaction from a job well done.
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Old 04-14-11, 02:18 AM   #3
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Yes, the TA's are ISO. You can also dial in the chainline with thin spacers inside of driveside if your using a cassette-type bb with fixed cup. I have yet to fit mine so do get back with what length you settled on!
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Old 04-14-11, 05:45 AM   #4
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I agree that the taper likely won't be as much of an issue as will clearance, i.e., will the Campy spindle be long enough. Personally, I'd mate the TA crankset with the TA BB. The BB/spindle that worked with the 3-pin TA crank should work fine with the cyclotouriste as long as you're not setting it up as a triple.

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Old 04-14-11, 07:26 AM   #5
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Thank you sirs for the info. I'll measure everything today and go from there. For some reason I thought that Campy had it's own taper.... Thanks again!
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Old 04-14-11, 07:41 AM   #6
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FWIW - Here is a pic from Sutherland's manual on interchangeability as it relates to TA

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