[werm42]

Hello All,

So I've upgraded my 2013 Trek Marlin's crankset from the Shimano Acera (FC-M311) to the Shimano Alivio (FC-M430).

However, now that I've done this, the stock Shimano front derailleur will not reach the 3rd (outermost) sprocket. :madman:

To answer the "is he too stupid to breed" questions: yes the crank is properly installed and tightened all the way down on the square bottom bracket. The derailleur limiter screws are turned all the way out as well.

The derailleur cage simply will not reach the 3rd sprocket.

Full disclosure: the bike was set-up (from factory) as an 3x8, the new front crankset is "allegedly" designed as part of a 9-speed driveset. That being said everything i've read here and elsewhere would indicate that there shouldn't be anything different between the crankset and front sprockets on an 8 or 9 speed bike.

Your thoughts, ideas, or suggestions are greatly appreciated. My only option i can think of now is to go to my LBS and buy a new front derailleur with a "greater reach".

 

[yourdaguy]

Did you try to adjust the limit screw?

 

[werm42]

To answer the "is he too stupid to breed" questions: yes the crank is properly installed and tightened all the way down on the square bottom bracket. The derailleur limiter screws are turned all the way out as well.

yes.

 

[yourdaguy]

Is it the same square taper bottom bracket? Square taper cranks will press on with different chainline on the same bottom bracket and with way different chainline on different bottom brackets. If it is a different bottom bracket then you probablyl got the wrong bottom bracket. Square taper Shimano bottom brackets generally come in 3 sizes.

I have pressed the came crank arm on the same bottom bracket and because I did not do it as tight, the chainline changed so square taper is susceptible to this problem, but most likely if you changed the BB you got the wrong size.

 

[yourdaguy]

By the say, sorry I missed the limit screw thing, I was originally doing this on my phone and my eyes are 60 years old so I miss a lot on my phone.

 

[werm42]

Just did some digging around online for the bottom bracket specs. I have 2 bits of information to go on:

1.) The directions from Shimano (included in the box with my crankset), state that a Shimano-model Bottom Bracket is compatible— part no.: BB-UN26. Looking up the specs for the BB-UN26, the measurements I found are: 68x122.5mm

2.) The OEM bottom bracket (on this bike currently) is VP-BC-73, from VPComponents which also claims to have a measurement of: 68x122.5mm


Truly stumped???

 

[werm42]

Nevermind: 73mm would probably indicated the VP-BC-73 Bottom Bracket.

So if i switch to a 68mm BB, i should be able to slippety slide the crankset on my bike without fishing for a new front derailleur, that probably doesn't exist.

 

[yourdaguy]

Yes