Banzai

Here's a puzzle.

Current setup: Nashbar cross frame, 135mm dropout spacing. Shimano HT II road triple. Chainline 45mm, near perfectly symmetric q-factor and crank offset from the chainstays.

I decided I wanted to go with a compact double. I figured it would be easy...just pop in the appropriate HT II crank, each side would shorten about a millimeter, and I'm set.

What happened instead was the drive side was considerably shorter, with the crankarm nearly rubbing the chainstay, and the chainline was way jacked. (I didn't measure...but it was very very wrong.) I tried to put the spacer that goes on the non-drive side with the triple on the drive side for this setup...but what happened was while the spacing got closer, the non-drive side crankarm no longer had the axle fully inserted. It didn't strike me as very safe that way.

I'm baffled. In theory, with the external bearing BB, I wouldn't think this would be a factor. I thought it would adjust symmetrically with the appropriate crank.

I'm not missing parts, and the only spacer I've ever seen is the non-drive side triple spacer.

Maybe the answer is a square taper BB.

On a tangent, does Shimano still make those? They don't show on the Shimano website. Nor do any non-"series" components, or simple brake levers, or bar end shifters, etc.

Thoughts on my dilemma are appreciated.

operator

Shimano square taper bb's are a dime a dozen. It's actually external that's going the way of the dinosaur next year. Square taper will be around for much, much longer.

I don't have enough experience with ext bb's to say anything. Someone else definitley should.

Banzai

Wish someone else would. Thanks for the reply though.

It's my understanding that while Octalink/ISIS was short-lived, external bearing will be around to stay. And, like I said, Shimano doesn't even advertise the existence of square taper on their website anymore.

Ex Pres 

Shimano still makes square taper BBs to support old cranksets, but does not currently make any sq taper cranksets

Banzai

I still don't understand why the chainline was so jacked, and why the crankarms were spaced so asymmetrically with the swap of the triple to the double. Like I said, in theory it should have shortened the q-factor just a bit, but both the arms should have moved in the same on each side, and the chainline should have fudged by a mere 2mm at most.

I'm flummoxed.

joejack951

Scroll all the way down for the square taper BBs: https://www.universalcycles.com/shopp...p?category=347

The crank arm coming so close to the chain stay could be just the result of the smaller q-factor and the 135mm rear spacing. Shimano may have designed that crank mainly to be used on 130mm spaced road bikes. The chainline is likely affected in much the same way by the wider spacing. You might just need to live with it being a little off from perfect. Can you take a picture?

Banzai

I may have to revisit this topic with a picture. I installed the crank on a different bike, and it's a bit late on a work night to start pulling bikes apart.

Perhaps during the week, or after the HH100, I'll do some crank swapping and take pictures. If anyone has more thoughts without pictures needed, I'm all ears.