Banzai

I have an XD triple crank that I intend to install on a build for Mrs Banzai.

I mounted it with one BB, and I noticed that the left crankarm sat considerably (several observable millimeters) farther from the frame/chainstay than did the right. I tried with a different BB, you know, just in case there was something wrong with the first. Same problem.

Then I took the digital calipers to the arms. The left, at apparent equal insertion, measures 1mm "tighter" than the right.

I went to the LBS to gripe (I bought it from them) and they started telling me that crank symmetry is no big deal, it doesn't have to be symmetric, then proceeded to point out several bikes in the shop with asymmetrically spaced crankarms...all of them with Sugino square taper cranks.

So. Are they right? Or are Sugino cranks not as good as they're cracked up to be? Or do I just need to learn to accept such imperfection in this build?

Replies are appreciated.

tellyho

I'd have to say that most of my bikes (all square taper) have the non-drive crankarm sitting further inboard. I assumed it was standard and never questioned it.

Banzai

It's easily a 4mm difference, maybe 5mm. Instantly naked eye visible, not something I discovered by measuring a finished product. It's the left crank arm that sticks out further.

joejack951

Interesting find. The Truvativ crank that came on my Specialized Hardrock suffered from the same issue. I found out when I installed a new bottom bracket. On the new BB, the non-drive side crank sat out quite a bit further than before. This didn't make sense at first as it looked ok on the old BB. I measured the old BB and sure enough the square tapers measured differently, with the non-drive side being smaller. I ended up replacing the crank along with the BB (bearings were shot in the original).

Not sure what advice to give. Hand-filing to fit seems like a sure-fire way to ruin an otherwise good crank but so does having a crank arm barely engaged on the square taper spindle. Perhaps a letter to the company is in order.

Retro Grouch 

If it was my bike I'd probably put a 2mm spacer under the drive side of the bottom bracket. That'll even everything out.

Banzai

Interesting. What would you recommend for a spacer?

sfclearwater

Most of the old square tapers I have seen are asymmetrical, usually the longer side is the drive side. When making single speeds I usually flip these around to bring the crank inboard. Never had a problem with the non drive side crank arm being out a few more millimeters. Even with newer stuff they are asymmetrical sometimes. I had a pair of shimano UN-53s, a 110mm and a 107mm. The drive side was exactly the same length but the non-drive side was 3mm longer on the 110.

Anyway my point was I would not worry about it a few mm difference. Although you should measure the clearance between the crank arms and the chain stays (unless this is already how you measured it), just to see how different it really is.

Banzai

That is how I measured.

The BB is a Shimano UN54. The two sides of the spindle are symmetric.

sfclearwater

Right. Well I am not sure what kind of BB a new Sugino XD is made for, but I had a look at a couple of my bikes and the older Sugino cranks I have around seem to be made for asymmetrical spindles. What I mean by this is both sides of the crank will be the same distance from the chain stays when the drive side spindle length is a few millimeters greater (as far as I can tell by a quick look anyway). Maybe your crank is designed for an asymmetrical spindle?

As Retro Grouch said, put in a 2mm spacer in the drive side and that would effectively create an asymmetrical spindle. Your LBS should have these spacers available.

TallRider

a millimeter or two is no big deal. 4-5mm is starting to be noticeable while riding, perhaps.

I'm pretty careful to make sure that have the right bottom bracket to get both correct chainline and have symmetrical crankarm spacing.

Retro Grouch's suggestion of the 2mm spacer would even out the symmetry but might throw off your chainline. Measure that - you want 45mm chainline with a triple (distance from frame's centerline to the middle chainring).

I have an XD triple on my Centurion Comp TA (see my sig for pictures) and achieved proper chainline and basically symmetrical spacing with a 110mm square-taper bottom bracket.
And I think the 110mm square-taper BB (both shimano and JIS-compatible made by other manufacturers) has the left side of the BB spindle sticking out 2mm more than the right. The drive-side of the 110 is the same as a Shimano 107mm square-taper BB while the non-drive sticks out 3mm further.

So to me it seems weird that you say your BB is symmetrical AND the non-drive-side crankarm is further away from the frame's centerline. Maybe you have a different XD crank than I do, with different crankarm symmetry?

Here's a picture of my CompTA from under the bottom bracket:

Psydotek

I've built 2 fixed/SS bikes using IRO cranks and bottom brackets. The drive side crank seems to sit further in than the non-drive side on both bikes. Unfortunately, i'm not comfortable with the idea of removing and reinstalling square taper crank arms once the mounting bolt has been torqued down properly...

Retro Grouch 

PM me a USPS address and I'll hook you up.

sheba

One cause of this could be the actual frame. Is the bottom bracket exactly centered? Or maybe someone faced the bottom bracket improperly and took more material off one side than the other.
Anyway.

On two of my bikes I have spacers in the BB to make the cranks perfectly centered. Cassette spacers are actually the same size as BB spacers. You can get some here. Or I used extra pieces from my Surly singlespeed spacer kit.
Good luck.

TallRider

Good thought. My two old Schwinns have an asymmetrical BB shell, still 68mm but I think shifted to the non-drive-side - which would account for your issue...

Booger1

A 3/16-1/4" offset over 30"(inseam) is not much of an angle.I'd set up the chainline correctly and call it a day.

CHenry

The assymetry. if you need any depends on the crankset , triple vs double,and whether the chainstays require more offset on the drive side than usual (most don't).

Deanster04

The bike may have originally required an asymmetric spindle with the longer side on the drive side. The chainline is the crucial factor to worry about. Just make sure the chainline is correct (google Sheldon Brown Chainline). if the non drive side is in or out more that the drive side is shouldn't make any difference to your riding. See how the bike rides and don't point it out to Mrs and she will be really happy to be riding the bike.
I recently had to replace a 135mm spindle (symmetric) and found it wasn't possible to find that length. I found an assymetric spindle 131mm that allowed for the correct chainling and the 5mm on the non drive side isn't noticable (unless I look). Good luck.