jignall

I'm converting my Trek 520 to a single speed and want to replace the current triple crankset (which has an integrated bottom bracket) with a Sugino Messenger crankset and accompanying square taper bottom bracket. My question is how do I determine which spindle length I should be using? The BB on my Trek 520 looks to be wider than other road bikes I have seen. Prior to swapping to a different triple crankset, I used to have a BB with a 118.5 length spindle I believe -- but this would only be appropriate for a triple crank, correct? If anyone can help with how to measure/determine what spindle length I need for a square taper bottom bracket that would be used for a single speed on my Trek 520 it would be great. Or conversely if you just happen to know the length that would be great too!

Thanks in advance.

Jeff

fietsbob

You Have measurements to do Chain line, and the Q of the crank are 2 ( arms on same side rather than crank placed

measure how far apart they are with one BB on it , and see how much width the chainstays
are where the crank arm passes by..

and in this situation, you will need a lot of pictures of each step in the process for remote help here ..

Internet sellers wont be any help , they will ship you parts, But, you need a local bike shop ..

Chombi

I've seen BBs at 103mm width being sold for SS/FG applications, so that could be a good legnth for you. 118mm was pretty common for double cranks in the 80's specially with French bikes with Stronglight or TA cranks, but 118mm must have been appropriate for non-French triples. 113mm was the typical legnths to accomodate double cranks like Shimano DA.

Chombi

Ex Pres 

The Sugino Messenger should have a recommended BB info with it.

Edit: quick Yahoo search came up with 103mm JIS all around, that is if you are using a 42mm chainline.
Are you using a proper 42mm hub/wheel in the rear?

Retro Grouch 

I don't know how much help it is, but I can tell you what I would do.

1. Trial fit your selected crankset with any bottom bracket that you happen to have on hand.
2. Install your rear wheel with the cog in place.
3. Now you can align a straight edge against your chainring and easily measure how far in or out your crank needs to go for perfect alignment.

Bradley P

I've seen search results with that also. More digging showed it as a 45mm chainline with a 103mm BB. Ben's Cycle sells the Messenger crank with a notice highlighted in RED about it. Maybe there had been some misinformation somewhere.

Bradley P

I am not a bike mech, but as I understand it, basically you would need to know the chainline for your crankset and also for the rear cog. If for example the rear cog is 45mm and the front crank is 42mm then you need to move the crank out 3mm. With a symmetrical spindle you need to increase its length 6mm. If the crank's 42mm was achieved with a 103 then you'd need a 109. Shimano UN54 are available in 110mm. That'd put the example off by 0.5mm. If the crank chainline is greater than the cog's then you need to move it in. This was a problem with a thread on another forum I read about the RD2 crank, someone had a 42mm cog and the RD2 was 45mm with a 103mm BB. Maybe there are some spacers that can be put in the back to move the cog out.

As I understand it the Sugino XD cranks do have a 42mm chainline with a 103mm BB. I think they are cheaper too. They are 110BCD.