UKC

Just installed a new bottom bracket and it went really well!

But now it won't shift into the large front cog....

Why?

Have i potentially not tightened up the BB enough and that extra fraction of a mm is meaning the cog sticks out too much?

Tedious....

In reply to KingStapo:

Maybe just that the front mech needs tweaked coz you've been fannying about with the chainset.

In reply to KingStapo:






try adjusting the big chainring stops.

In reply to KingStapo:

What cranks and old/new bb are you using?

In reply to KingStapo:

Before fiddling with the front mech make sure that is the root cause of the problem.

Assuming this is a threaded external bearing type BB check you have the correct number of spacers, of the correct thickness, under each bearing.

In reply to a crap climber:

Shimano cranks and new Shimano BB. No idea what the old BB was but it looker fairly similar to the new Shimano.

No amount of fiddling with the front mech makes it shift better...

In reply to johnwright:

What are the big chain ring stops?

In reply to KingStapo:

Need more info than that!

If you have an external bb (i.e. Hollowtech II cranks):
- check you have the bb spacers in the right place. If you have a road bike there should be no spacers. For a mountain bike it gets complicated. If you have a normal front derailleur, i.e. not an e-type, add a spacer to the drive side. If you have a 68mm shell add a further spacer to each side.

- check you are using the right type of bb. Shimano road and mtb bbs have slightly different widths

If you have a cartridge type then check you are using the correct spindle width.

If you have a press fit bb then good luck

In reply to a crap climber:

More info:

Bike - Specialized Allez Compact
http://www.evanscycles.com/products/specialized/allez-compact-2012-road-bik...

New BB:
http://www.evanscycles.com/products/shimano/un55-bottom-bracket-ec031943?ut...

My only thought is that the square tapers on the new BB look a teensy bit bigger than on the old, as such the cranks and cogs sit a bit further out.

Should be within the realms of front mech adjustment though right?

In reply to KingStapo:
If you have the old bottom bracket it would be worth measuring that and comparing it to the new one that you bought they should be the same length if not it may explain the issues that you are having.


This would probably be the cheapest place to get a new bottom bracket if you need to http://www.rosebikes.co.uk/article/shimano-bb-un55-bottom-bracket/aid:51514...

In reply to KingStapo:

Screw it - thanks for all the help - but i've just popped it into the local bike shop to get it re-calibrated. Matey reckons it's not uncommon for front derailieurs to need a tweek after a new and different BB goes in, everyone makes 'em slightly different sizes I guess...

Front derailiuer adjustment looks like it's something i don't want to get involved with just yet - i'm quitting whilst ahead at a 'successful' BB swap.

Next up is rear cassette changing and mastery of a chain whip.... I've heard nasty stories!

In reply to KingStapo:


Get some pipe lagging and wrap it round the cassette

Oh, and don't be put off by the horrible noise when you apply pressure, the lockring always makes that noise for the first half turn or so,