thehammerdog

I want to replace the old to small for me 170's cranks on my old Grandis circa 1982. How can I tell what type of BB it is? I have a great older dura ace crank I want to put on but not sure if it will fit on the current BB and then if not what thread do I need?
I am plannning to get 28mm tires and go gravel grinding.....huge amount of tire space.

Torchy McFlux

1) 170mm cranks used to be a "universal" size for everyone except the very tall and very small. What makes you think you need something larger?
2) An '82 Grandis would be considered a nice vintage Italian bike. Are you sure you want to be removing original era-appropriate components and use it for "gravel grinding"?
3) There are many different iterations of the Dura-Ace crank - each requiring a different bottom bracket axle size. You need to mention the exact year or model number (usually stamped into the inside of the arms) to figure out the type you need.
4) Grandis is an Italian brand, so it likely has an Italian threaded BB shell.
5) Not sure if you're being sarcastic, but 28mm wide tires are probably as wide as you'll be able to get away with. The Grandis bikes I'm familiar with were of road racing design - not the best for use off pavement.

FBinNY 

Given the vintage you almost certainly have a classic square taper BB, which you can replace with a similar one, or a cartridge. The issue will be spindle length. Over the years, they've increased the offset in crank arms and shortened spindles to increase stiffness and reduce weight. So whatever modern crank you buy will likely require a shorter spindle.

IMO- you have 2 basic options.

1- buy square taper cranks, and replace the spindle with one the right length if necessary (probably will be).
2- replace both the cranks and BB, opening up the field to include any modern crank with any compatible 1.37x24 (ISO/BSC) bottom bracket system

thehammerdog

I ride a 56 use 172-175 on all my bikes the cranks are short 165's the frame is small 54. I like it because it is all old school Galli Gold groupo nice but I cannot really ride it as I want. I do have old school square taper cranks but I am aware that not all square tapers are the same not do I know how to tell if it is Italian, english or what ever BB threads. The space between frame and tires now with 23's is huge 28mm should fit.

thehammerdog

IMO- you have 2 basic options.


2- replace both the cranks and BB, opening up the field to include any modern crank with any compatible 1.37x24 (ISO/BSC) bottom bracket system[/QUOTE]

I like this option as I can get a crank & BB new very cheaply on line but I am not sure how to determine the type of threads or what size spindle I need.
Thnaks

Kopsis

For threading you measure, then you go here: Sheldon Brown's Bottom Bracket Size Database . In general, if your BB has a 1 3/8" thread diameter (about 35mm) and the drive side cup is left-hand threaded, chances are it's BSA. If your BB has a 34 mm thread diameter and the drive side cup is right-hand threaded, you have an Italian BB.

You'll need to read the article to figure out how to measure chainline and compute what spindle length you need for different cranksets.