rothenfield1

As a follow-up to my previous post asking about determining spindle length, it occurred to me to take another approach. I have an old Sakae Ringyo SX 130/74 ‘triple’ crank that I am trying to get a BB for. Velobase has a listing for a ‘double’ matched to a recommended 117mm BB. Does anyone know what the recommended BB length is for the triple.

Just to complicate matters, I’m probably going to buy a cartridge BB which would be symmetrical versus an asymmetrical bearing and cup BB, if that makes a difference?

This is a long shot I know.

https://velobase.com/ViewComponent.as...115&AbsPos=163

mechBgon

If I'm not mistaken, there's an old SX down at the bike shop. I'll fit it up on Monday and let you know what looks right. My guess is 125mm plus or minus 2.5mm. What's your seattube diameter, since that affects how far in the FD can swing?

HillRider

The closest next size up is 122.5 mm and that will probably work.

rothenfield1

Thanks to both of you. MechBgon, that would be fantastic. Geez, that’s a good question about the ST diameter, I haven’t gotten that far yet. I’m building a vintageTrek 500 frameset into a 9 speed and was going to try and use the SX triple with ramped and pinned inner rings.

Just confirmed the ST diameter as 28.6. Just curious, how does ST diameter figure into the BB length equation?

mechBgon

As the diameter of the frame tube goes up, the FD sits half that much more outboard of the centerline, and the frame tube sits half that distance closer to the FD's inner parallelogram arm (other factors being equal). If I had a dollar for every time I've had to deal with a FD bottoming its parallelogram against the frame tube without getting clear of the chain in the granny ring, I could have pizza RIGHT NOW

mechBgon

I have the Sakae SX mounted on a 122.5mm UN-54 here and that looks like a good length for it.

Bill Kapaun

IF your current spindle is not symmetrical, chances are you can flip and be just fine.
I've ran into very similar bikes from the same mfr., where one was a triple and the other a double.
They used the same BB parts, but the "long" end for the triple.

rothenfield1

That sounds convincing enough to me to start looking for a 122.5 cartridge. Determining chainline from scratch is still a magical mystery tour to me. I don’t suppose it matters if the rear has been spread to 130mm and I’m trying my first mod to 9spd?

rothenfield1

I don't have a spindle to work off, just a frame and a crank, but that's an interesting idea about turning the spindle around.

Booger1

That triple crank on my touring bike took a 127.5....it's an offset BB.

HillRider

IIRC, that's the longest UN-XX bottom bracket Shimano offered. I had to use one to get nds (yes non-drive side) crank arm/chainstay clearance on a '93 Trek 7000 MTB since the chainstays were so fat.