SR500 touring bike Bottom Bracket question

[John Simpson]

I have a 1986 Cannondale SR500 touring bike. I have upgraded the shifter cables, brake/shifter levers, rims/wheels, and derailleurs and as a final upgrade I would like to replace the bottom bracket bearing assembly. Any advice as a compatible sealed bottom bracket bearing assembly that would fit the threads and also integrate with the original crank arms (with the square holes) for this bike? I would consider replacing the cranks if need be to allow the more modern bottom bracket to be utilized.
Thank you,
John

 

[black lightning 1987]

The ST500 was the touring bike model, it had a Shimano 600 triple crankset. The SR500 had a Shimano 600 double. The BB threads are 68 mm x 1.37 English. I'm pretty sure the double used a 116 mm spindle. Velobase lists the spindle length of the FC-6206 triple crank as 121.5 mm. There are several NOS BB-6207 bottom brackets for doubles on ebay. Some are listed as 115 mm but I'm guessing that's due to sellers faulty measurement.

https://www.ebay.com/itm/Vintage-NO...a:g:~bcAAOSwu~5byK3f:rk:5:pf:1&frcectupt=true

A cartridge bearing equivalent would be the Shimano BB-CT91 or the Sunrace of the the same length.

https://www.ebay.com/itm/New-Old-St...V:rk:2:pf:1&LH_ItemCondition=3&frcectupt=true

https://www.ebay.com/itm/SUNRACE-BO...t:rk:1:pf:1&LH_ItemCondition=3&frcectupt=true

The Token is a lot nicer than either of the above, also comes in 122.5 width which would work for the triple.

https://www.ebay.com/itm/TOKEN-Squa...w:rk:3:pf:1&LH_ItemCondition=3&frcectupt=true

Here's a NOS 121.5 BB-6207:

https://www.ebay.com/itm/New-Old-St...b:g:usMAAOSwkXFb0e-g:rk:1:pf:1&frcectupt=true

A cartridge equivalent would be the UN55 with 122 mm spindle:

https://www.ebay.com/itm/Shimano-BB...S:rk:2:pf:1&LH_ItemCondition=3&frcectupt=true

 

[John Simpson]

Thank you very much for your reply! I will be in a much better position to order the right part now. Enjoy your day!