m2usa

The bottom bracket (Dura Ace 7400, size 68 - 112mm) in my '90 RB-1 finally up and croaked. The ball retainer cracked which then scored and pitted the spindle. It was mated to a 7402 Dura Ace crankset. I can't seem to find a replacement spindle with the same measurement. The closest so far is 113mm. Will this spindle work properly, or will it potentially change the chainline by forcing the crank offset? I see that the Shimano UN-73 sealed unit is also sized at 68-113 which may be the easiest swap if the sizing will work. I'd appreciate your comments. Thanks!

TallRider

Get out a metric ruler and look at 1mm. And now cut it in half, because the difference is spread out on each side of the bottom bracket. Do you think that will mess up your chainline? The piece of dust that your chain picked up from the road will mess it up more. Go ahead with the 113.

Some Shimano bottom brackets are asymmetric (usually with the non-drive-side spindle sticking out further than the drive-side), but assuming that all cancels out with this crank, you'll be fine.

simplify

Also make sure to note the measurement between the bearing races on the spindle. Those can vary, so make sure they are the same distance apart and from each race to the spindle end, as they are on your old spindle.

HillRider

This is a non-issue with the current cartridge bearing designs.

TallRider

Unless you're comparing a cartridge BB that's symmetrical with one that is asymmetrical.

simplify

Right, but that's not what the OP was looking to replace. As I understand it, the original spindle had bearing races, which were damaged by a broken retainer. So if he's looking to replace just that spindle, then that dimension is an issue.

m2usa

Thanks for the info. Yes, 1 mm is a very short length, but I wanted to make sure it wouldn't cause any chain rub on my FD. For the most part I wouldn't think that it would on the RB-1, but on my other bike the 105 setup (which btw is a 10spd setup) is very temperamental about chainline and 0.5mm does make a difference on that setup (otherwise the chain rubs.)

In any case, it appears that going with the UN-73 is the safest bet compared with replacing the spindle only (the dimensions are asymmetrical with the drive side length being approx 3mm longer). I can live with having a sealed system instead. Thanks for your help.

HillRider

I think a small adjustment to the limit screws, cable tension or fd angle would correct this problem more than a 1 mm bb spindle difference.

m2usa

Yeah, that's what I thought. I'm running a CR1 with an R700 compact crank. It works fairly well, but the 105 FD limit screws were too restrictive. I had to actually use a dremel tool to file them down about a 1/32 of an inch to get the FD to not rub on 50/12 or 34/25. I really did try all the angles on the braze on mount as well. In any case, I put the UN-73 on the RB-1 and it's running well. Thanks for the suggestions.