wle

so

old bike
gt road bike, probably an 'edge'
1998 or 1999

(EDIT - correction, the new cranks are not octalink, they are hollowtech..)

i acquired some compact cranks
shimano FC-R700

the BB is currently square taper

stats are
British I.S.O. 1.370" X 24 tpi
Shell Width /Standard 68 mm/O.S. 73 mm

what do i have to have and get and do, to put the new cranks in, or is it possible?

i don;t really see what would keep them centered
the crankset has 100mm of axle bare
then the BB shell is only 68mm wide, what takes up the other 32mm?

usually the BB includes the axle but these things have an axle but no bearing..

i am just too old school, help.. !




i;d like to have the things just work but that is looking less likely

thx
wle

dr_lha

I don't believe you have an Octalink crank, you have a Hollowtech crank. You need to buy external cup bottom bracket to go with it. Something like this will likely work:

https://www.amazon.com/Shimano-SM-BB4...ywords=bb-4600

You'll need the tools to extract the old BB and install the new one.


Answer: The bearing cups.

wle

you are right, i will edit orig post...
wle

triplebutted

Not sure If I understand the question. You have the cranks? And there is a BB installed on the frame? You can get any compact crank that will use an English BB. You can do current Shimano compact, Mega Exo, etc. You just need the correct English BB that will work with that crank.

dr_lha

OK. BTW don't worry your bottom bracket shell is extremely standard. It will work!

Without seeing your old setup, it's difficult to tell, but you'll likely need this tool to remove your old BB:

Amazon.com : Park Tool BBT-22 Shimano Sealed Cartridge Bottom Bracket Tool : Bike Hand Tools : Sports & Outdoors

and this tool to install your new one:

https://www.amazon.com/Park-Tool-BBT-...bracket+wrench

wle

i think i also have to have the shell machined for flat/parallelness, right?

wle

fietsbob

External Bearing Cranks would comed with the Bearing assemblies , in the Carton. But not the installation Tools .

Compact in road stuff now = 34-50t chain ring combinations .

Staying 'old school' .. the 110 BCD crank type will build up with the same chain ring Choices.. in square taper type.

AnkleWork

Maybe try a test fit?

wle

yeah i bought cranks used, is why i am confused
bearings prob stayed in a bike somewhere
it is 50/34T

wle

wle

yes i already have the cranks.
bike has old square taper BB as i listed, english 68mm
think i need
external BB for hollowtech
tool for hollowtech
face the BB shell
(already have tools to get old BB out)

wle

dr_lha

It may not be necessary, depending on the condition of the frame, but it certainly can't hurt. Likely as the frame wasn't built with external bottom bracket in mind, there will be paint on the outside edge of the BB shell, in which case facing will be needed.

wle

yeah i bought cranks used, is why i am confused
bearings prob stayed in a bike somewhere
it is 50/34T

wle

wle

no paint, oddly the frame is naked aluminum, GT idea i guess

what would happen if i tried not getting it faced, and it actually needed to be...?

wle

dr_lha

If it's really bad, you'd notice that the bearing cups don't screw down flush to the end of the BB shell. I'd definitely get it faced in that case. IMHO if it looks good to the eye, I wouldn't bother, but others may have stronger opinions on this.

triplebutted

Ahh I see. Yah, as others noted, it'll be easy. Just need the correct English BB for the cranks. For your original octalink, you will need the splined tool. You will be all set and riding in no time!

alcjphil

If you just have the cranks you will need to buy the matching external bearing bottom bracket. Facing may or may not be necessary, many older square taper bottom brackets required that tha BB shell be faced to do a proper installation. Good news is that external bearing bottom brackets are relatively inexpensive, even the higher end ones

wle

right
ok
thanks everyone
tiagra BB for $15
BB tool from bikehand for $13
crankset used for $5

bonus, the BB and chainrings were worn anyway!
had 48,000 miles plus, on both

win - win
cheap cheap

also just got different back derailleur [ancient shimano 600] that i believe can handle the extra chain range
will try it without refacing the shell, of course, first

wle

wle

spacers, how do i know if i need them?

wle

HillRider

Spacers are needed if you have a crank meant for a 73 mm (typically on an MTB) bottom bracket shell but are installing it on a 68 mm. You have a road crank so no spacers should be needed.

BTW, Hollowtech (plain Hollowtech, no numbers) did indeed use an Octalink bottom bracket. The newer Hollowtech II cranks use the external bottom bracket bearings and have the spindle built into the drive side crank arm.

My criteria for crank alignment with Hollowtech II cranks is does the spindle slip through both installed bearing cups with no forcing or bending? If it does, your shell is adequately parallel. If you have to force it into line, even a little, have the shell faced.

wle

thanks, exactly what i needed to know, plus wanted to hear
wle