Bicycle Mechanics - Replacing old square taper cranks

I'm in the process of swapping out the cranks on a friend's the bike. The bike is a semi-abused Trek VW Limited Edition from 1996 or so. The old cranks were Sugino Impel and the new ones are also Sugino Impel. The problem is that I can't get the new cranks far enough up the BB spindles, so the front derailleur doesn't have enough reach for the largest chainring. I'm guessing I need a new BB with shorter spindles, right? In the past 10 years, have square taper cranks has gotten some sort of universal upgrade that?

Although all square spindles have a 2-degree taper, there are/were two different final cutoff widths. I am guessing from your post that the new cranks have the smaller size bore. If I am correct, forcing them onto the larger-width spindle is an invitation to crank failure, as well as the bad chainline you have already observed.

Yeah, you need a shorter BB spindle. Older crank arms were more or less straight, and needed the wide spindles...newer ones have a sort of "S" bend offset, and use a much shorter spindle...

Yeah, you need a shorter BB spindle. Older crank arms were more or less straight, and needed the wide spindles...newer ones have a sort of "S" bend offset, and use a much shorter spindle...

Dura ace square taper bb's used to come in 103 version. Now the smallest bb you can get is a 107. If anything bb's got longer, not shorter.


I'm in the process of swapping out the cranks on a friend's the bike. The bike is a semi-abused Trek VW Limited Edition from 1996 or so. The old cranks were Sugino Impel and the new ones are also Sugino Impel. The problem is that I can't get the new cranks far enough up the BB spindles, so the front derailleur doesn't have enough reach for the largest chainring. I'm guessing I need a new BB with shorter spindles, right? In the past 10 years, have square taper cranks has gotten some sort of universal upgrade that?


What length bb are you running right now?

Um, the Dura-Ace crank that used the 103mm spindle was from around '96, older models used longer spindles...

http://www.sheldonbrown.com/bbsize.html

Read this: http://sheldonbrown.com/bbtaper.html

If anything bb's got longer, not shorter.

I guess that's why Campy Record used to use 115mm spindles in the mid 70s-mid 80's, 111mm mid 80's-90's, and 102mm for their last square taper model :rolleyes:

What length bb are you running right now?

Current bb is 113mm.

And now I'm further confused by reading this on Sheldon Brown's website:

"If you install an ISO crank on a J.I.S. spindle, it will sit about 4.5 mm farther out than it would on an ISO spindle of the same length.

Confersely, if you install a J.I.S. crank on an ISO spindle, it will wind up about 4.5 mm farther in than it would on a J.I.S spindle of the same length."

The problem I'm having sounds like the first example, but I know the new cranks are JIS, so if the old bb was ISO, I'd be having the opposite problem. Has there been a change in JIS standard? Or do the old cranks just have a slightly narrower boring than the new ones?

Just for fun, measure the distance between your rear dropouts.

I'm looking in last year's QBP catalogue and it says Sugino Impel 150X-154-158 series cranks should take a 110/113 BB spindle length. The rule of thumb is you use the shorter spindle with 130mm dropouts and the wider with 135mm dropouts.

If your front derailleur isn't reaching I'm thinking that your chainline is way off. How much space do you have between the chainrings and the chain stay? I'm thinking you have something goofy going on but, off the top of my head, I can't think of what it might be.

Dropouts are 135.

Measure your spindle length and compare it with what's spec'ed for the new crank. I sure wouldn't just assume that 10 year newer cranks would automatically fit the old BB spindle length. You might need a new BB.

oops. sorry. missed your last post. my next step would be some trial and error on different BB's from my junk drawer.

For the record, 103mm bottom brackets are still available from sugino. I believe campy still makes their 102mm bb as well. Aside from their track cranks, sugino has never used the ISO standard, so that probably isn't your problem. Your cranks are definitely JIS as are most of the replacement bottom brackets available.
The problem may be that the older cranks had been overtightened a bit and sat further up the spindle than the new cranks. If that is the case, you may just need to re-adjust the limit screws on the front derailleur. You didn't mention if you had don't that, so I apologize if you've already tried that.
Sheldon's site says the correct length is 110-113, so the easiest thing to do may be to get a new 110mm bottom bracket. I recommend this one (http://bikeparts.com/search_results.asp?ID=BPC124254) but there is both a cheaper version, and a lighter, more expensive version.

I guess the best way to figure it out is to go get a 110 and a 113 bb and see which one works. I'll try installing the 110 first because the old 113 doesn't seem to be the right size. One of the two will be right. I hope.

Does this bike have the cup/cone type spindle or a cartridge BB? If the former, AND you serviced the bearings, maybe you installed the spindle backwards? Many of them have an offset, where the DS is longer than the NDS.