Chainring Clearance & Shimming Cranks

[BobbyJones]

Can't remember if this was discussed here before so I'm bringing it back up-

When building my bike, the inner 39t chainring was VERY close to the chainstay, maybe a few millimeters. I put a wrap or two or three of electrical tape around the cs to see if there would be any rubbing and I'm now seeing the tape is getting hacked a bit.

Soooo how close is too close? What's the word on shimming between BB / Crank arm? How the heck do I go about this?

Octalink 109 English BB with Ultegra 6500 Cranks.

Thanks!

[kramnnim]

Shim/spacer between the flange of the BB and the face of the BB shell?

[oliver1850]

I would do what kramnnim suggested if you need clearance. As I remember the Octalink BB left cup has no shoulder, so you should be able to put a shim under the right one and gain a little clearance. It will offset your crank a bit, but it sounds like you don't need much.

I can tell you how much clearance is not enough, because I have the issue on my Colorado II. I knew the clearance was very close when I built it up, and noticed on my last ride that there is now paint missing. Just from memory, I would say I only had 2mm clearance, but can measure it.

[sean]

With the spacers, I've had better luck with the steel ones. The alloy ones tend to compress a bit.

[oldpotatoe]

Can't remember if this was discussed here before so I'm bringing it back up-

When building my bike, the inner 39t chainring was VERY close to the chainstay, maybe a few millimeters. I put a wrap or two or three of electrical tape around the cs to see if there would be any rubbing and I'm now seeing the tape is getting hacked a bit.

Soooo how close is too close? What's the word on shimming between BB / Crank arm? How the heck do I go about this?

Octalink 109 English BB with Ultegra 6500 Cranks.

Thanks!

2 options. Steel spacer under the RH cup flange as long as the LH arm clearance to the chainstay isn't an issue or...

if the frame doesn't have a indentation in the chainstay, like it oughta, make one. If metal bike, lay a socket at the appropriate place and smack it..done this more than once.

[RPS]

2 options. Steel spacer under the RH cup flange as long as the LH arm clearance to the chainstay isn't an issue or...

if the frame doesn't have a indentation in the chainstay, like it oughta, make one. If metal bike, lay a socket at the appropriate place and smack it..done this more than once.
Isn't there a third option of using the longer bottom bracket from a triple? If I recall correctly it's about 9 MM longer (109.5 versus 118.5). Of that 9 MM I think a little more than half is on the drive side.

Granted he probably doesn't need that much more clearance unless he may want to install larger 42T or 44T in the future.

I personally wouldn't "smack" the chainstay unless the bike is a beater, and a junker at that.

[oldpotatoe]

Isn't there a third option of using the longer bottom bracket from a triple? If I recall correctly it's about 9 MM longer (109.5 versus 118.5). Of that 9 MM I think a little more than half is on the drive side.

Granted he probably doesn't need that much more clearance unless he may want to install larger 42T or 44T in the future.

I personally wouldn't "smack" the chainstay unless the bike is a beater, and a junker at that.

I don't think the FD will work very well adding that much to the BB spindle.

Serotta's, titanium ones, have always had a problem with FD inward travel on triples. I have modified more than a few seat tubes with this common problem on Legends. It really is nothing different than the frame maker does.

[RPS]

I don't think the FD will work very well adding that much to the BB spindle.

Serotta's, titanium ones, have always had a problem with FD inward travel on triples. I have modified more than a few seat tubes with this common problem on Legends. It really is nothing different than the frame maker does.
He hasn’t said what kind of frame it is but I’d guess that if there is clearance concerns it’s “probably” not steel; and hence uses larger OD chainstays and probably other tubes as well. I may be guessing wrong though. More info would be nice; and maybe picture too.

In this case it would be limited more by outward travel, and to some degree it depends on what size his seat tube diameter is. The larger the seat tube diameter, the less of an issue it should be.

Isn’t what you described above usually the opposite – larger OD seat tubes (like some oversize ti) tend to push the front derailleur out so far that it’s hard to get it to move inward far enough to get proper shifting into the granny chainring? If oversize, shouldn't it help matters here?

[oliver1850]

I ran into the inward swing issue with the CII as well. I was trying to keep the Q factor as small as possible and used a 111 mm BB. I wanted to use a C Record FD, but with the 35mm seat tube it wouldn't swing inboard far enough. A Veloce 9 with the screw all the way out has barely enough travel to work. In my case, I think I'll just put a 115.5 BB in and solve both problems. For the OP, I'd think a 1mm shim on the right cup will probably be enough. I will try to measure the clearance on my CII and get back to you.

[BobbyJones]

Hey there. The frame is a steel Soma Smoothie ES.

There is a factory indentation, but its mostly closer to the seat tube and obviously isn't enough to cover this. Looks like my FD will cover the swing, and the opposing crank arm has enough clearance.

Can anyone make a suggestion on where to pick up a spacer. Is this something like a Wheels Mfg. part? Looks like they make them in Alu?
http://wheelsmfg.com/content/view/492/42/

Thanks for the suggestions.




He hasn’t said what kind of frame it is but I’d guess that if there is clearance concerns it’s “probably” not steel; and hence uses larger OD chainstays and probably other tubes as well. I may be guessing wrong though. More info would be nice; and maybe picture too.

[kramnnim]

I've used cassette spacers...think I had to grind away some of the spline/teeth things. Perhaps the thin steel spacer used under 10sp Shimano cassettes? Obviously the Wheels Mfg spacers would be better, but maybe not as easy to find.

[oldpotatoe]

He hasn’t said what kind of frame it is but I’d guess that if there is clearance concerns it’s “probably” not steel; and hence uses larger OD chainstays and probably other tubes as well. I may be guessing wrong though. More info would be nice; and maybe picture too.

In this case it would be limited more by outward travel, and to some degree it depends on what size his seat tube diameter is. The larger the seat tube diameter, the less of an issue it should be.

Isn’t what you described above usually the opposite – larger OD seat tubes (like some oversize ti) tend to push the front derailleur out so far that it’s hard to get it to move inward far enough to get proper shifting into the granny chainring? If oversize, shouldn't it help matters here?

What I said, large seat tubes, flared out, limits inward travel of the FD(Serotta Ti) and doing something to the seat tube(dent) to allow for inward FD travel.

[oldpotatoe]

Hey there. The frame is a steel Soma Smoothie ES.

There is a factory indentation, but its mostly closer to the seat tube and obviously isn't enough to cover this. Looks like my FD will cover the swing, and the opposing crank arm has enough clearance.

Can anyone make a suggestion on where to pick up a spacer. Is this something like a Wheels Mfg. part? Looks like they make them in Alu?
http://wheelsmfg.com/content/view/492/42/

Thanks for the suggestions.

At a bike shop dear liazza, at a bike shop....

[LegendRider]

if the frame doesn't have a indentation in the chainstay, like it oughta, make one. If metal bike, lay a socket at the appropriate place and smack it..done this more than once.

I just read an interview with a Bissell mechanic who talks about this very thing (though, not on their Pinarellos!). I believe he was a national team wrench and had just received some steel track frames from an overseas builder. Not enough clearance for the size rings they wanted to use, so a ball peen hammer was utilized.

[oldpotatoe]

I just read an interview with a Bissell mechanic who talks about this very thing (though, not on their Pinarellos!). I believe he was a national team wrench and had just received some steel track frames from an overseas builder. Not enough clearance for the size rings they wanted to use, so a ball peen hammer was utilized.

Actually very common with wrenches who have been around metal frames for a while. Campagnolo even has a little chart for such a thing for their front ders, where to dent it and how deep.

[LegendRider]

Actually very common with wrenches who have been around metal frames for a while. Campagnolo even has a little chart for such a thing for their front ders, where to dent it and how deep.

Aren't builders doing something wrong if this is necessary?

[oldpotatoe]

Aren't builders doing something wrong if this is necessary?

I would say so. I see lots of brazeon tabs that make the FD very tail high on steep seat tubes, smallish frames. And as I mentioned, have seen triple crank/FD 'issues' on more than a few legend Ti frames.