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My left syncros crank was recently backed into by a car. The cranks are 175 mm. The bottom bracket is also syncros brand, threaded, and the size is 68 x 110mm. enter image description hereI have a syncros triple chainring, 5 bolts, chainring sizes are 24, 34, 46.enter image description here I'm hoping to get a fix that involves a new crank/BB) without having to change my whole drivetrain. Would there be any other brands compatible with vintage syncros parts?

From what I gather, they are square taper, which would be ok except that they are iso. The shimano products I've come across are square taper JIS. I was hoping to keep the same BB, as it is running smooth and is titanium (light). The chainrings and shifting have also not been problematic, so was hoping to keep them as well. This is all new to me so my research may be sketchy at best. Thanks for any help :)enter image description here

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  • Are you funding this or is the car driver? Ethically, they should pay to repair what was damaged, and anything further you choose to spend is on you.
    – Criggie
    Aug 9 '21 at 0:10
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    Technically, we are both funding it; my husband backed into it in the garage. (I was trying not to shame him, lol.)
    – She-ra
    Aug 13 '21 at 15:55
  • GRIN sorry! Tell him to tidy up the garage as additional penance, and find somewhere to store the bike/s safely. There are hanging options which can use up otherwise-deadspace, either on the walls or in the rafters. That's a whole separate question though.
    – Criggie
    Aug 13 '21 at 23:28
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You do have a lot of options, although high quality square taper x3 cranks will be new old stock - almost impossible to find, or used. You could find a used set, which are fairly common as people are upgrading to 1x all the time, or donor bike, and if needed, swap the chain rings with your existing ones (which means flogged out chain rings on the donor set do not matter).

If you don't mind the weight gain, there are still square taper x3 cranks available in lower cost brackets. If you Bottom bracket is not in perfect condition, now would be good time to change to something more modern than square taper.

Depending on gearing you use, with a new bottom bracket, you could get reasonably high quality new components in 2x.

What to do depends heavily on the condition of the drive train. If its near new then replacing just teh crank with a used one is probably easiest and cheapest. If its completely worn out, then replacing it with a new drive train might be more economic in the long run. If you replace the entire drive train, it opens you up to the installing kit from the likes of Micro shift which offer better pricing than the tier one manufacturers.

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  • At the time of writing this, Specialites TA is still selling high end square taper cranks and triple spiders and Sugino and Stronglight have slightly less fancy ones. You'd probably need to replace the bottom bracket with one that fits the new cranks, and going two-piece would probably be cheaper and better option.
    – ojs
    Aug 13 '21 at 19:17
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As @mattnz alludes to, this is a good time to think about what you like and what you don't like about your current drivetrain. Do you like the shifter type (e.g. trigger vs gripshift)? Do you like the action of your current shifters? Do you like your gear ratios?

You can certainly get by without changing anything other than the BB and crankset; in that case, you'll want similar tooth counts on the chainrings of a 3x crankset compatible with x9 rear cassette and chain.

You have an aftermarket crankset; BB technology has advanced since your square taper BB, and today's "external bearing" BBs are considered superior while similar in price. Many will actually thread into the same shells as the square taper BBs, and so are straightforward upgrades.

Shimano's Hollowtech II BBs perform well at reasonable prices, but there are other brands that will also fit you BB shell width and threading. Normally, one chooses a compatbile crankset/BB combo. With Hollowtech II, you can purchase an older new old stock or used higher end crankset and a new current Hollowtech II BB, or stick with a (fairly) current crankset like Shimano's FC-T4060 cranksets. The available tooth counts for the latter are either 44/32/22 or 48/36/26, so your rear derailleur should work fine with either (if you change your maximum tooth count or range too much, you may need a different RD to handle the new range).

Remember also that unless your chain and cassette are quite new, they will be somewhat worn; it's worth installing a new chain with the new crankset, and perhaps a new cassette as well.

PS - Photo of brass caliper (4") that costs about $5 at US home improvement stores.

enter image description here

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    @mattnz and Armand, So I managed to find a vintage syncros crankset with shimano triple (not cheap probably due to obscurity) I've located a new vintage syncros titanium BB (my present one seems to be ok, but thinking it may be a good idea to have the spare, also rare and somewhat pricey). Do bottom brackets have to be exactly the same length (I know the width needs to be the same). How much difference might a frame accept, and would that difference throw off any other bike component functionality? Can frames that came with iso bb take jsis bb's? Thank you both for your helpful insights.
    – She-ra
    Aug 13 '21 at 18:33
  • For the frame, what matters is the threading of the "shell" and its width (common widths are 68mm and 73mm). Sometimes, 73mm BBs are used on 68mm shells with spacers to make up the width difference, so measure your actual shell width with calipers if possible. The needed spindle length is determined by the crankset. Isis is an obsolete BB standard that uses a splined spindle end rather than a square taper, but should be available in threading and width that fit standard "BSA" shell threading and width.
    – Armand
    Aug 14 '21 at 1:43
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    I was having trouble understanding your comment until I realized I wrote JSIS rather than JIS. (I see where the confusion about "Isis" would have come into the conversation). I will edit that. Also, I've never measured with calipers, I will have to get my hands on some.
    – She-ra
    Aug 15 '21 at 10:10

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