braintree39

Hi Everyone,

I'm building up a bike for the first time. I'm looking to find the bottom bracket spindle length. I have a used Suntour XC LTD Triple Crankset. I'm putting it on a Surly Cross Check.

Any suggestions? - I can't seem to find it. I asked in a bike shop today and they told me it would be best to bring it in and have them install it. (Which kind of defeats the purpose of doing it myself... I really want to learn more than anything!). I imagine there is a way to measure or calculate the spindle length... If nothing else, I could just roll the dice with a 68x122.5 and see how it goes... (that seems to be the length of other cranksets that may be similar to mine.)

Go ahead and school me! Your help is appreciated...

3alarmer 

...try a 126 to start. I think that's correct, but I'm going off their earlier triples in the VX series. I think those were all made for them by Sugino, but again I'm not familiar with that particular crank.

Retro Grouch 

The crankset is the single most significant factor in determining spindle length.

My method is to test fit the crank with the widest bottom bracket I happen to have on hand. Once you do that, it's a simple process to measure the chainline figure out how far you'd like to move it in, and subtract twice that amount from the BB spindle length.

braintree39

Ok - Great! So it sounds like I'll have to just try one out, hope I get it right, and possibly order a second if I get it wrong... I don't have any on hand since I'm pretty new to this. I'm ok with that. For the purposes of learning, it's a small price to pay.
@3alarmer - the only ones I can find are either 122.5 or 127.5... Sooo... What would you go with between those two???

dedhed

VeloBase.com - Component: SunTour XC LTD

Says D-3TS spindle which according to this is 128mm but I don't know if that is symmetrical.
Pictures don't look symmetrical.
https://www.ebay.com/itm/SR-JAPAN-D-...-/202142334619

3alarmer 

...sounds like 127.5 is the way to start. Maybe order a couple of spacers to slip in on the drive side under the sealed unit lip to give yourself a little adjustment option in case you need to push it a little farther out because of interference between the chainring and the chain stay. It's more of an art than a science, but you definitely don'[t want to start out short.

The spacers come in different thicknesses, and you only need a couple, if you need one at all.

You might be able to pick those up locally, and not buy a whole package of them, if yoiu're not planning on doing this again soon.

dedhed

Looking further at the ebay ad, in the description they state 40mm - 49mm - 39mm as the dimensions so almost symmetrical.

Bill Kapaun

Looking at my charts, anything with a T? has a 39mm offset on the DS.
The symmetrical equivalent would then be 130mm.(2*39+52)
Get the longest you can find and hope it's long enough.

braintree39

Hmmmm... Starting to think that I should have gone in a different direction. I bought this crank used for $15 - maybe I should just take that as a loss and buy a newer crank. (I wasn't totally happy with it anyway, I just figured I'd start with something cheap.) Perhaps I could buy something a little more straightforward? With more documentation of compatibility? Any suggestions?

Ideally, I was looking for a double - perhaps even a 1x. So getting a Triple that I'm going to run as a double seems like it might not have been a good move.

Any thoughts? As I said - I'm trying to learn as much as possible. Thanks!

Bill Kapaun

If you are going to drop the inner ring, then you "might" be able to use a shorter spindle.
It'd depend on crank arm to chain stay clearance.

Sometimes "too short" simply means the FDER can't move IN far enough to reach the inner ring.
Sometimes a good deal has a root cause.

braintree39

Well - I went ahead and ordered the 127.5 UN55 - per 3alarmers recommendation - we'll see how it works. If I can't get it going, I'm sure I'll learn something in the process... I'm not dead set on sticking with this crankset... And I'm open to recommendations if anyone has any...

Bill Kapaun

I would give odds you'll be "good enough" to function.

Another alternative is reverting to cup & cone and using a 3T spindle from here-
https://www.huskybicycles.com/mm5/me...y_Code=BBPARTS

I can't attest to quality though. I've used a few on flip bikes, but have no clue how well they held up.
The races had a "rust brown" finish, not polished. I kind of expect an x-mart quality level from appearance alone.

braintree39

I wonder if I'd be better off just buying a more modern crankset - something like this:


https://smile.amazon.com/FSA-330-647...145&th=1&psc=1


Or this:


https://smile.amazon.com/Origin8-Pro...&sr=8-46-spell


What do you think?

3alarmer 

...you already have this crank. While compact cranks have their place in this modern world, the one you now possess was a pretty solid product, and with the triple, you can get a wider range of gearing without going to extremes on the rear cluster in terms of sizing. It really depends on your vision, and the availability of various components you intend to use in your project.

But any forged crank is a pretty good product.

3alarmer 

...I should probably explain a little further. Whenever I build up a project bike now, I have already figured out the gearing I intend for it (which depends a lot of projected use...go fast, touring, all around city bike, etc).

For any particular bicycle I use here, because the terrain is often pretty flat and the hills are mostly short ones, I can usually get by with the older standards of 52/53 large chainrings. This still allows me, even on something pretty old, to squeak by with a 14-25 or maybe a 13-26 cluster on the back. If I went with compact cranks, I'd spend my life looking for stuff with 11 cog small rings.

Anyway, good luck with it. And if you have some success or other issues with the fitting of it, check back. I think maybe your original instincts of trying to go with used stuff that is cheaper in this first project were sound. There is a lot of used componentry lying around looking for another use cycle. But again, it depends a lot on your own unique wants and needs.

bikeman715

127.5 mm bb is what is use with this crank .

braintree39

Awesome! Thanks for the input. I've ordered the BB. Now just waiting....

braintree39

This was all really helpful. Thanks.

63rickert

The reason the LBS wanted you to bring it in and let them do it is that the fastest and most dependable way to determine spindle length is often test assembly. Even when it is a well known model of crank and everything looks normal there are quirks and quiddities and out of spec product. Putting the bike on the stand and trying spindles is way easier and more reliable than consulting references. Presuming of course you have some inventory.