more advice pls, bb axle length/crank - stay clearance

[timdrayton1]

right, still doing my retro build.

the driveside crank seems awfully close to the stay when rotating, nothing touchs but there only 2 or 3mm in it.

the bb is a square taper, and the cranks are old m550's

is this ok or do i need different cranks or bb, can i space out the bb (i am thinking not as the axle is likely one piece?)

help with jargon, cheapest route would be good?

had a look at sheldon brown here

http://www.sheldonbrown.com/bbsize.html

this says the cranks (m 550) need a length of 122.5, is this axle length required? so do i just need to shop around for some cranks which require less length? any suggestions?

 

[jimihendrix]

EIN?

 

[timdrayton1]

that was wierd wasnt visible, is now!

 

[laurence]

Hi Tim, If i were you i'd replace the bottom bracket with one the right size for your chainset i.e 122mm. Shouldn't cost you more than about £15.00. If your axle is the wrong length you may find it difficult to get the front mech to work correctly.

 

[jimihendrix]

A, Ah, some words and a picture

The chainstay clearence is close but you would probably get away
with it to be honest, as long as you can get the front mech to work as Laurence suggested.

Do you know what width the BB is you have in at the moment ?, if
it's a Shimano sealed unit it should be marked on the shell, axle width
is also dependant on the frame as well as the cranks, some frames
have wider or thicker stays than others. Not possible to "space out" an
axle but some expensive BB's have adjustability for altering the chain
line.

 

[retroyetirigid]

I've often found with M550 cranks (same goes for M250/300/350/400/450/500/650 and 730 as well) that if they are a bit worn on the taper, as happens if they have been removed a few times, that I've had to use a 127mm axle. Especially on alloy frames.

 

[blueyes]

yes, the old shimano cranksets of the 80s to 90s (XT M730, DX MT60, LX M550/250/300/350/400/450/500) require BBs with long axles as can be seen in this table:

http://www.shimano.com/publish/content/ ... le.html/05)%20Crankset%20and%20BB%20Combination%20Chart.pdf

if the crankset is relatively well taken cared of meaning the taper hole isn't rounded or deformed just get a BB of 122.5 for a 47.5mm chainline or 127.5 for a 50.0mm chainline

or you can shop around for a new crankset/BB combo

 

[Splatter Paint]

That's a great link - cheers.

SP