BB/crank spacers/shims
 

My house and bike stuff are a shambles right now, getting new carpet, so I cannot easily get pictures. My problem: I replaced an Ultegra 6500, 175mm crankset on a 2003 Lemond Poprad, with a used 170mm Dura Ace 7701/03, both doubles. After mounting the 7700 crankset set, adjusting the shifting and taking it for a ride, I was wiping it off when I got home and realized the inner chainring is extremely close to the chainstay. After a while of trying to figure out why, I measured the housing of the cranks that the spindle loads into and the Dura Ace is about 1/8 inch wider on each arm. I did not measure the distance between the chain ring and the crank arm before I removed it, but suffice to say it is not much. Question 1: How much clearance is needed between crank arm and chainstay? Question 2: To achieve that clearance do I need to change the BB to one with a longer spindle or are there spacers/shims available that would work? When I took it for a ride everything was working fine, but that small amount of clearance worries me.I looked at my other bikes and they all have considerably more clearance than on the Poprad, even with the 6500 installed. I am thinking that when the 6500 crankset was installed by the previous owner, the BB should have been replaced at that time.Originally it was a Sora crankset. Any info and suggestions on my questions are appreciated.

Spacers won’t make a too short spindle longer. The crankset determines spindle length so yes you need a BB with a spindle of the correct length for the crankset you put on the bike. In most cases some amount of mismatch is ok, it just means your chainline won’t be optimal. But if way off, you get problems like the one you have where you risk damaging the chainstay for lack of clearance between it at the crank. All that being said, I am surprised that the ultegra and dura ace cranks aren’t using the same spindle length. What BB is in there?

2 or 3 MMs of clearance from the stay after tightening down the RH arm is what I look for. Do know that what you add in spacers behind the RH cup will take away from the lockring's needs on the other side. Andy

I pulled the BB from the Poprad today., BB-6500/68/BC 1.37 x 24 with a length of 109.5. I have done a couple of searches and the only other size I find with 68 English is with a spindle length of 118.5. I also looked for 7700 Dura Ace and no good option with that search. One of the descriptions for the 118.5 states it is for 3 speed FD. Also, to me, that seems like too long of a length from the 109.5. Any help with this would sure be appreciated. If the 118.5 is workable, will this BB5500 be compatible? https://www.ebay.com/itm/Shimano-105...kAAOSw2H1dx2an? Thanks in advance for any insight into this issue. Just remembered, If I need to use spacers instead, where would I locate them?

More info: The clearance between the inner ring and the chainstay with the 6500 crankset is about 7mm, and with the 7700 it is only 1.5mm. It seems to me that the BB with spindle length of 118.5 should work. If the 5500 BB is compatible, one source I found says it is, I can get a new one for quite a few dollars less.

The 7700 and 5500 both use octalink v1 spindles so the 118 5500 should work fine with your crank. And you’re right, there really aren’t any octalink options between 109 and 118. Make sure, though, that your FD has enough reach to shift with the longer spindle.
Another option would be going smaller on the inner chainring unless you’re already as small as you can go, which I think is 38 for that crank.

38 T is the smallest ring for 130 bcd and that is what I have on the 7700. I did not even think of checking the reach on the front derailleur. I will check it but am pretty sure it will be ok since I had to shorten the travel when I first tried the 7700. I bought this bike used, and while I am working on it, I am going to install new gear and brake cables. I am also going to upgrade the old Sora FD with a new 5700 that I had bought and never used.

I used to have some 2mm spacers for under the drive side of the BB. Problem solvers, maybe as a source?

Have you measured the chainline at the chainrings? If you take a measurement, it will help to determine how far you want to bring the chainrings out. Typical road chainline with 130mm dropout is 43.5mm. I have mine at 44mm, with 7.6mm spacing center-to-center between the chainrings, although the spacing can go up to 8mm. You can add spacers under the right side BB to push it to the right a little bit, but not to the left. You might want to also check whether or not the left and right crank arms are symmetric, so you can decide if spacing or longer spindle works better for you. JIS square taper BB is sometimes not symmetric. I don't know if octalink has this issue.

1.5mm clearance is plenty for me. Pretty sure my fixed-gear has less. ;)

update
 

I re-installed the 6500 BB and crankset. The BB is OK but not great. I now have clearance of 1.6 mm between the small ring, 38T, and the chainstay. I calculated a chain line of 41.35. By those figures I believe a bb with a shaft length of 118.5 will be too long. I think my best option now would be to purchase a new bb with the length of 109.5 and either one spacer of 2 or 2.5 mm or two 1mm spacers. I am not sure, but I thnk I did not see a 2mm spacer. I think I will pull the 6500 crankset and bb again, then re-install the 7700 crankset and see what figures I get from that. Then decide the best way for me to go.

Wheelsmfg makes aluminum BSA spacers of 0.7, 1.8, 2.5mm thicknesses.
https://wheelsmfg.com/bottom-bracket...ack-alloy.html
https://wheelsmfg.com/bottom-bracket...ack-alloy.html
https://wheelsmfg.com/products/botto...ack-alloy.html

Shimano MTB BBs for hollowtech 24mm spindles all come with 3x 2.5mm plastic spacers. I have a whole bunch of unused ones. But I would prefer aluminum.

So you're off spec a little. What actual functional problems are you experiencing?

Update/Success
 

I received the 5500 BB, 68 1.37x24, with a length of 109.5. Also the 2.5 spacer for the drive side of the BB cup. It all worked out well. The clearance between the small ring and the chainstay is now at 4mm and the chain line is 43.85. I also adjusted the position of the FD to accommodate the change, and installed new gear cables. Everything is working great on the workstand. Tomorrow morning I am going to install new brake cables and adjust the cantilever/brake pads. I purchased a fork mount cable guide and I am hoping that cuts down on the shudder and noise. The Campy Zonda wheels I purchased have wider rims than the Open Pro rims that have been mounted on the bike. Hopefully, I will be riding the Poprad tomorrow with the Dura Ace crankset, Zonda wheels, new cables and a just cleaned and lubed chain. WooHoo! My confidence and willingness to learn and do more bike mechanics/maintenance has taken another step. It takes me more time than mechanically skilled bicyclists, but for me, that is a good thing. I need to be focused and be sure of the process to get things done correctly. Once this bike is done, I can move on to two other projects I have in line.

delbiker1,
Glad to see you are progressing in your mechanic travels! I am currently putting parts on the 59 cm Ocshner to sell it. Lot of 600 parts and some 105 mixed in but it will be a good rider for someone when it is done. I will post pics when ready for sale. I trust all is well, MH

So I take it that inserting the spacer on the drive side didn't reduce the clearance between the non-drive side crank and BB shell, or between the non-drive crank and the non-drive side chainstay? Well, at least not so much that it rubs/hits on the frame?

Dan

The NDS crank is closer to the BB shell and the chainstay. However, I believe the clearance is wide enough to not be an issue. At the BB shell, the clearance is 6.3mm. At the pedal end of the NDS crank arm, the clearance is 4.75mm to the chainstay. This morning, I installed the new brake cables along with the fork mount cable stop. I did not mount the Zonda wheelset. I am going to leave them on my Airborne Zeppelin. It is looking like I am not going to get in shakedown ride today.The wind is blowing 17 to 22 mph and gusting to close to 30 mph. It is also raining and it looks like that is going to get heavier in the next hour or so. Maybe a quick lap or two around my neighborhood.