Problem with new chainset and old front derailleur

mba007
mba007 Posts: 95
edited May 2008 in MTB workshop & tech
Earlier on today I replaced an old worn chainset with a new Shimano M442 Mega9 Tapered Chainset. But it is clear that the existing front deraiileur hasn't got the reach to put the chain onto the largest chainring. I've adjusted the screws so that they allow the derailleur to be moved to its furthest possible position by hand but it isn't enough. The chainset is installed tightly (using my nice new Parks torque wrench).

The main issue appears to be that the new chainset sits further away from the BB than the older one. The secondary issue appears to be that the deraiileur hasn't enough reach.

Thing is, I have no idea whether I'm making a problem out of nothing, whether this is a common issue, or whether I need to upgrade my front mech.

Any advice is appreciated :)

Comments

  • supersonic
    supersonic Posts: 82,708
    So did you get a new bottom bracket? What is its length compared to the old one? What is the mech and frame?
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  • mba007
    mba007 Posts: 95
    The front derailleur is Shimano Acera, and the bottom bracket is non-descript. Both have been on the bike from new (which was about 7 years ago). The bike is a Giant BoulderShock, so nothing to knock your socks off, however I really like the ride of the 'steel' frame so am upgrading bits as they die.

    I've decided to replace the BB with a new Shimano version in the vain hope that the axle will be shorter and suited to the new chainset.

    I did read somewhere that older BB axles were longer and hence there can be issues when upgrading, but this was from an uncorroborated source, hence my question on this forum.

    Thanks for taking the time :)
  • mba007
    mba007 Posts: 95
    Just ordered a BB with an axle which is 7mm shorter... a BS standard triple UN54 square tapered. According to my measurements this will move the inside cog 8mm towards the BB which, hopefully, will work... we'll see.

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