Bicycle Mechanics - How do I know if I can install a specific crankset on a bike?
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12-28-12, 12:21 PM
To be more specific:
I have an old Bianchi Campeone del Mondo, which came with a Shimano Sora gruppo. The crankset on the drive side got damaged in an accident, and I have to remove it. This is a bike, it is important to add, that I want to use on the trainer and/or as a back-up for my mainstay bike. Let's call it A
OK, so now we move to a box I have with the components that were removed from a Bianchi Veloce, circa 2000, whose frame was damaged. I have the 175mm triple, and wonder if I can move it to A. I also have its square-taper BB, whose specs are a thread of 1.37x24, but whose spindle length I had to measure without calipers and I am pretty sure comes to 110mm. On the back of the crank itself, the only marking is 54T. Let's call that Bike B
Now, back to bike A. The crank bolt must be frozen, because I can't for the hell of me remove it, whereas the non-drive side pops out easily. Therefore I cannot yet access the BB. However, the crank does have a model number on it (FC3303), which is 170mm. The BB is a BB-UN25. Here, i get little confused, because for the triple, it says that the spindle length is 113mm; however, the same exact model, if with the double, is 110mm (I think I'm just a little surprised that a different length would not warrant a different model number).
My question is what other variables I need to know in order to assess whether this transfer is possible? Another angle is, could I transfer the BB from Bike B to Bike A, along with the crankset? In this case, what variable would I need to look for?
12-28-12, 12:58 PM
First, you should be able to install the triple from bike B onto bike A. if the width of the BB shell matches between the two bikes, you can install either BB in either bike. Measure the length of the BB shell. If they both read 68 mm, you are good to go.
Second: is it that you can't remove the bolt that holds the crank arm on, or can't remove the crank from the spindle after the crank bolt is removed, or can't remove the drive-side of the BB from the BB shell? This last one is probably a reverse pitch thread, the opposite of say, and standard lightbulb. Either way, you can get these little things done at a bike shop. Should only take a good tech with the right tools 5 minutes.
Once you have the BB from B in the A frame, snug it up with the wrench and see how the crank from B fits on the A frame. If you think you need to do trial installations before you are satisfied that all is well, you need to get a crank extractor, which will pull the crank arm off of the square spindle after it's been tightened on. It will not just pull off with your hands. Removing it is easy with an extractor, and
extraordinarily hard without one.
If you want to go by the numbers: The model numbers of the BBs do not tell you the length, they tell about the lightness of the materials each BB is made of. UN-71 is one of Shimano's highest, and UN-26 is one of the lowest, for square-tapered ends. More critical are the length of the spindle (the "110" you noted) and the thread (you should have something like "1.370 x 24 tpi" if i recall). Shimano makes all lengths of BB spindle in all grades of BB. Your UN-25 might be a 110, but another UN-25 might be a 126. The 126 will be very odd to set up and ride if 110 was what came on the bike, but they could be theoretically the correct part number. You really just need to measure the spindle length and consider that number a match TO THE CRANKSET primariy, Secondarily it is a match to the frame. It is NOT a match to the UN-xx number. The "54" is the number of teeth on the biggest chainring. It doesn't affect fit of the crank to the bike. It does affect the chain.
So when crank B gets installed on frame A it needs BB B or another Shimano UN part with the same spindle length and made for the same BB shell length.
The arm length 175 mm does not affect fit of the BB to the frame or the crank to the BB. It does affect the fit of your leg to the crank/bike combination.
12-28-12, 01:12 PM
When you say the "crank bolt must be frozen" are you referring to the bolt that holds the crank arm to the spindle or to the bottom bracket cup itself?
If the crank fixing bolt won't unthread (it's a standard right hand thread) it may have been bent or damaged in the accident you referred to in your first paragraph. You can either use more force and try to remove it through brute strength or cut the crank arm at the eye in two places and remove it destructively. In either event the crank and bottom bracket are probably throw-aways.
If the problem is with the bottom bracket cup itself, be sure you are turning it the correct direction. English bottom brackets (which you have) are left hand threaded on the drive (chainring) side and unthread clockwise.
As to the UN-XX number, Shimano made a variety of quality levels for their cartridge bottom brackets with the higher numbers being lighter and having better bearings so a UN-5X is lighter and better than a UN-2X. It has no relationship to spindle length, crank arm length or chainring size. And, yes, triple cranks typically use longer spindles than doubles.
its the non-drive side that has reversed threads on the pedals (and on a british 68mm BB). assuming ths is square post stuff, both sides use normal bolt threads on the center bolt that holds the cranks onto the BB axle.
if I was where you are, I would be using some AeroKroil
on that bolt, also tip the bike so the drive side is down, and dribble some Kroil onto the back of the crank right where the BB axle goes into it, hoping it will be able to run down the corners of the square shaft and get to the bolt from the other side. I might even squirt some into the other end of the axle so it runs down the middle of the axle and hits the threads from the other side. let the kroil work for a couple hours, then put a BIG wrench on the crank center bolt, and use the crank arm as the counter lever, pushing both DOWN to break the bolt (facing the drive side, crank arm at 3 o clock, wrench at 9 oclock, pushing both down should loosen that bolt).
Kroil is the best penetrating oil out there, but somewhat hard to find. Kano Labs sells it to the airline engine business. If you can't find AeroKroil, you can try 50% red ATF (Automatic Transmission Fluid, the traditional mercon+dextron style that you'd use in a 80s/90s car), and 50% Acetone. acetone is extremely volatile, extremely flammable, and somewhat toxic, so use outdoors and avoid breathing the fumes or getting it on your skin. symptoms of acetone exposure are like a really bad hangover.
...As to the UN-XX number, Shimano made a variety of quality levels for their cartridge bottom brackets with the higher numbers being lighter and having better bearings so a UN-5X is lighter and better than a UN-2X. It has no relationship to spindle length, crank arm length or chainring size. And, yes, triple cranks typically use longer spindles than doubles.
and not all triples are the same, either. I recently replaced a cheap Tourney style triple with a Origin-8 "Trekking" triple, both were 48-38-28, but the Tourney used a 122.5mm axle, while the Origin-8 needed a 110mm for the same chainline. Origin-8 claimed 113mm but their spec was for a 50mm chainline (mountain 3x9 style), and the Shimano spec for the stock parts on the bike was 47.5mm (cheap hybrid 3x8).
12-28-12, 01:23 PM
AFAIK Bianchi USA, has been jobbing out to TW contract factories for a long time, so it may not be Italian,
so BB is not Italian thread.
12-28-12, 01:39 PM
I'm sending my thanks all the way to Ann Arbor. To answer the first question, yes, I can't even get the bolt off that holds the arm, so additional measures will be required before going into the bowels. I can't be very precise, but I do think both are 68mm in length (margin of error in mms is too high measuring with just a ruler). I don't think I can measure the width of the shell on Bike A until I get the crank off, so that will take precedent before all else.
Thanks for the education.
12-28-12, 02:00 PM
Before you dig in to the bottom brackets, try just a straight swap of the crankarms (once you get all 4 off). 1.5mm isn't a whole lot, and you might get away with it.
12-28-12, 06:40 PM
its the non-drive side that has reversed threads on the pedals (and on a british 68mm BB).
No. You are correct that the left (non-drive side) pedal is left hand threaded but the drive side English bb cup is also left hand threaded.
12-28-12, 08:19 PM
OK - I confess my primary school-level knowledge about these things. The best way I can describe the bolt that I'm referring to is that it has a hollow head, which means that it cannot be unwound with a wrench, but in theory with an 8mm Allen; a black protective rubber cover surrounds the head of the bolt. This is what you can see with the naked eye if you look at the crank.
then you need a 8mm hex bit that fits on a ratchet wrench to get enough torque on that, not just a typical L shaped allen wrench.. those center bolts are always normal threads, so it comes out counter-clockwise as you face it. pedal at 3 oclock, wrench at 6 oclock, and press down hard on both of them til the nut breaks free.
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