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PostPosted: Tue Mar 26, 2013 1:08 am 
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Bit of a problem
My bike has a bottom bracket (Square Taper UN52E) installed with the E Type bit for the front mech.
The previous cranks/rings were LX M570.

Anyway, I left the same Front Derailleur (LX M570 E Type) and installed some Compact 94 BCD Specialites TA rings and Raceface Turbine cranks.

Now the bottom of the Derailleur blade when extended, hits the tips of the inside of the teeth on the largest chainring!


Bizarre! Why would that be? Is there something I may have done wrong? They're supposed to be slightly higher and when extended inline with the outside of the large rings teeth?

I understand these cranks need a 107mm BB? Would I need to change that? but that doesn't account for why the mech is hitting the teeth - it seems the rings are too high for the mech, or the mech needs to be lifted up a tad.

I'm probably going to change the BB for a 107mm one and ditch the mech, to get an XT M739 which will clamp onto the tube instead - but before I go out and make more work for myself and spend money, perhaps there may be a solution which'll save me time and money?


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PostPosted: Tue Mar 26, 2013 1:53 am 
retrobike rider
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Joined: Sun Sep 23, 2007 11:22 pm
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E-type mechs work, so there shouldn't be any need to replace the mech. I can't quite understand what's happening from your description, but you certainly need the correct length bb spindle for the cranks. The flight path of the derailleur plate is at a diagonal angle, so if the spindle is too long, the plate will be too low to clear the chainring at the point that it gets there because it's too much towards the beginning of its flight path. If the spindle was shorter, the plate would be further into its flight path, and thus higher, when it reached the ring. Is this what's happening?

I also wonder what size the big ring is? I've never actually tried a 44t ring with an FD-M739E mech, but I presume it must work as they sold the FC-M739 with either 22-42 or 22-44 rings.


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PostPosted: Tue Mar 26, 2013 9:01 am 
retrobike rider / Gold Trader
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etype mechs are adjustable, i had same problem when i put an XT739 etype onto my C16R and also changed the Cranks, there is a small plate which you rotate 180 degrees and it gives a higher sweep clearing the chainring, difficult to explain but have a look see if you can see it?

Jussa :)


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PostPosted: Tue Mar 26, 2013 9:13 am 
retrobike rider
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Jussa, never used them. But do you mean undo bolt 4 ant turn 5 upside down then tighten both?
Image


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PostPosted: Tue Mar 26, 2013 9:16 am 
retrobike rider / Gold Trader
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FluffyChicken wrote:
Jussa, never used them. But do you mean undo bolt 4 ant turn 5 upside down then tighten both?
Image


Exactly, it gave me the clearance i needed when i changed cranksets :) nice exploding diagram mate.

PS - Hope you get some resolution on the loss of your bikes :( bad times.


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PostPosted: Tue Mar 26, 2013 10:29 am 
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Basics first -- does the new chainring have the same number of teeth as the old one?


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PostPosted: Tue Mar 26, 2013 10:47 am 
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Anthony wrote:
If the spindle was shorter, the plate would be further into its flight path, and thus higher, when it reached the ring. Is this what's happening?


Actually, it's the other way around. If the spindle's too short, the plates won't be high enough in their outward and up arc to clear the ring.

Do the above mentioned switch with the eccentric bushes. It's the adjustment for running different size/spread of chainrings.


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PostPosted: Tue Mar 26, 2013 11:40 am 
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MikeD wrote:
Basics first -- does the new chainring have the same number of teeth as the old one?



The old chain ring has 42-32-22T
The new one is erm 44-94

Ill have a look at the other thing when I get back from work


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PostPosted: Tue Mar 26, 2013 11:57 am 
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There you go then. New chainring bigger, move mech higher as others have said, sorted :)


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PostPosted: Tue Mar 26, 2013 5:35 pm 
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The mech is on the highest position

Bought XTR UN90 68x107 Bb and looking to get a top pull front XT M739 mech to clamp on instead
Can't be arsed with all this e type malaky and headache


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