andy_p

Hi all,

I'm doing up an old touring bike, and the bottom bracket is well and truly shafted. It's a 68x116 cartridge, which seems to be a fairly rare size. Will a 68x113 fit ok? As far as I'm aware, the main difference will be in the chainline, but it's only 1.5mm different. Has anyone done this swap, and will the front mech adjust for the change in chainline?

Thanks in advance!

oldskoolwrench

andy_p,

The big factor is whether or not the inner chain ring will clear the seat stay with the 3mm shorter spindle. How much space
is there between the inner ring & the seat stay with the 116mm spindle? The other thing to check is the other extreme;
with the current BB in place, check to see how much clearance you have between the Lg. chain ring and the seat stay.

That's your gauge; if you have at least 5mm of space between chain ring/ seat stay right now then the 113 will work. If
not then you could (1) find a 68 x 116 cartridge BB, (2) go to the LBS and see if they have a traditional BB spindle in 116mm,
or (3) try a 68 x 118mm cartridge BB. No chain ring/ seat stay issue, your chainline would be very close, and the 118 might
be more common. Test fit everything first, though.

HillRider

Shimano made a 68x115 mm UN72 cartridge which was the factory OEM for 8-speed Ultegra cranks. There were also 68x118 mm cartridges in a few models for 8-speed 105 triple cranks.

davidad

https://www.biketoolsetc.com/index.cg...TH-7420AL68116

andy_p

Thanks for all the advice! Might end up getting 68x115, didn't know the size existed (mind you, I didn't know much about bottom bracket sizes until today...)

ultraman6970

Next time you have a problem like this check out a few things...

1 the BB axle is symmetric or no...

2 length of BB axle.

3 how much room do you have between the chain stay and the small chainring.

Once you have all of that figured it out there was a big chance that you could have gone to an even shorter BB... from 116 to 113 looks like a lot but is not, it is only 1.5 mm per side... and many low end bikes come with insanely long BB axles. Even 5 mm difference is not that much because is just 2.5 per side and usually you have a lot more room than 2.5 between the chainrinng and the chain stay.

The nice about a shorter BB is that the Q factor gets more descent, and the chainline works better resulting in a smoother drivetrain.

Happy you found the answer to the problem...

Peace.

GeoKrpan

68x 115mm Shimano UN72 BB at Jenson USA, $17, a great deal.

I recently tried to replace a 68x115 BB with a 73x110 BB. I used a 2.5mm BB spacer on the drive side and it totally worked. But, there was a fly in the ointment. I put the drive side crank on first. The crank arm cleared the chainstay BUT the inside base of the crank arm came into contact with the BB cup.

If it were a 68x110 BB then it might have worked since there would have been 2.5 mm more spindle showing.

The crank is a triple with the inner ring removed. I thought I could get away with using a narrower BB but
it turned out not to be so.

andy_p

After careful consideration and re-fitting the old BB (which was pretty hard, as the cups were plastic and appeared to have been cross threaded at some point in their life), I went for a 68x115. Which of course didn't fit (inner chainring hit seatstay), so now I wonder how the original 68x116 was made to fit. Probably something to do with it being cross threaded, which might have made it stick out a bit more and clear the seatstay. Ah well. Another one on order......