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Limpet · **Posted** Sun Nov 8, 2009 4:26 pm

Hi just replaced a truvativ (five-d) chainset with a shimano (deore m442) but the new shimano doesnt go on far enough onto the square taper to position the big ring within the front mech's outermost reach, it only comes as far as flush and the chain will rub. Should i be fitting a new bottom bracket to go with the new chainset? I'm not sure what the brand the existing bottom bracket is. . . Any help would be really appreciated.

nicklouse · **Posted** Sun Nov 8, 2009 4:30 pm

have you adjusted the front mech?

does the new cranks need the same length axle as the old ones for the same chainline?

i guess not.

"Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
Parktools

SheldonBrown

Limpet · **Posted** Sun Nov 8, 2009 4:41 pm

I'm pretty sure the front mech is alredy at its outermost position. As far as i can tell the new crank and chainset are the same size as the old ones. I'm not really sure about the whole chainline thing- I thought i would be ok swapping square taper crankset for squaretaper crankset. I have heard some suggestion that slight machining differences between brands can have an effect, would this be enough to stop the crankset sliding on far enough?

nicklouse · **Posted** Sun Nov 8, 2009 4:48 pm

diferent cranks need different bb axle lengths

so measure your old one. look up the cranks on the service info from Sram and see what chain line it gives. (or measure it on your bike).

then look up the new cranks to see what axle length you need to give the same chain line.

Or measure the current axle and then someone might look it up for you.

Yes take the new cranks off and measure the axle.

"Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
Parktools

SheldonBrown

Limpet · **Posted** Sun Nov 8, 2009 4:49 pm

So the existing bb was 68mm x 113mm What bb should I buy to obtain the correct chainline? How can I work this out?

Limpet · **Posted** Sun Nov 8, 2009 5:20 pm

Cheers fro your advice nicklouse. I have looked on both technical sites and must admit I cant fathom it out. Still not sure what my chainline is or needs to be. perhaps I need a 110mm bb (shimano un26) just doesnt seem like 3mm will make the difference up.feel a bit of a thicko but if anyone has any guidance I'd be greatfull.

nicklouse · **Posted** Sun Nov 8, 2009 5:28 pm

yep you need a 110mm axle length.

"Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
Parktools

SheldonBrown

Limpet · **Posted** Mon Nov 9, 2009 9:44 am

Thanks very much nicklouse. Not quite sure how you worked that out! Will replace bb and see what happens. Have to say without assistance I would prob end up at lbs, which are all crap where I live so am very greatfull for your advice as it should allow me to be (fairly) independent. I am actually a cabinet maker and joiner by trade so if you need any wood advice I would be happy to offer my best braincells in return!!

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