Bafang 750 dual chainring problem

[Domino83]

Hi guys,
I have a problem with my bafang 750.
I mounted a dualchainring with precise alps 46 and 32 teeth.
My derailleur doesn't open enough for switch on 46 teeth chainring

What I should do?
Please help me
Regards


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[Benjahmin]

Not sure what you mean chap. Is it that your front derailleur doesn't move enough, or is it that the rear arm is making the chain too tight?

 

[Steve UKLSRA]

Looks to me like the jump from the two rings is far too big for the chain to derail even if you could get your front deraileur to shift out that far! Have you tried to back the adjustment screw right out?

 

[Domino83]

Not sure what you mean chap. Is it that your front derailleur doesn't move enough, or is it that the rear arm is making the chain too tight?

Looks to me like the jump from the two rings is far too big for the chain to derail even if you could get your front deraileur to shift out that far! Have you tried to back the adjustment screw right out?

w

 

[Domino83]

Which screws you mean?

 

[Steve UKLSRA]

Which screws you mean?

There's two silver crosshead screws on the top of the derailleur, one for the inner limit, one for the outer limit...back the outer one right out (anticlockwise) or even remove it, to see if you can get the reach...do it on in the garage though, don't try riding it!

 

[soundwave]

that is a 14t jump even if it went that far i doubt you would get the chain on there because the chain would be so tight on the 46 and to loose on the 32 to work with the gears at the back.

with the motor under load all i can see is snapped chains even trying to do it.

you need to adjust the screw that moves it as far right as you can but you will also risk bending the crap out of it as the jump is so big or the hole thing could snap off so try it in a bike stand first.

 

[Domino83]

I already tried with the derailleur 2 screws, but doesn't help enough

 

[Domino83]

I already tried with the derailleur 2 screws, but doesn't help enough

 

[Steve UKLSRA]

Your ring2ring ratio is too big (as I said in my first comment and SW also posted)...12 teeth seems to be the 9sp max and 10 the 10sp max, in my experience...and has your outer ring got ramp-pins on it, your pic doesn't show it...you can see the silver ramp-pins to help the chain move to the outer ring on this pic (excuse the wear, it's an old one!)

 

[soundwave]

lol dont matter what front mech you buy it is not going to happen the jump is just to big and even if it would go out more the sheer force would either snap the chain or rip of the mech under load.

all you can do is get a bigger rear cassette eagle 12spd is 10-50

 

[Steve UKLSRA]

Just fit a 38t narrow wide and run whatever cassette you want, although 11-36 is my favourite, it'll be good for 30mph on throttle and still climb anything you throw at it...all mine are set up like that

 

[Domino83]

Otherwise I should remove the small one ( including adaptor) and use only the 46? Do you think it should works?


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[soundwave]

one or the other will work but not the 2 together as is but imo the 46 will suck if going up hills and off road.

and that is even bigger and was useless

 

[anotherkiwi]

You need a direct mount derailleur and a problem solvers direct mount adaptor for a fat bike BB.

Second problem the number of teeth, the only derailleur that will handle up to 16 teeth is a Sora road derailleur the one that works with a 50-34 road compact chainset. And yep you guessed they only seem to exist in braise on or collar mount.

If ever you do find a direct mount derailleur that does 16 teeth please tell me where, I am looking for one myself. I want to run 48-32 on the front of my trike.

 

[Deleted member 4366]

The problem is with the reach of the derailleur. Some don't reach far enough to pull the chain in line with the outer chainring. I've had that with a couple of bikes after I installed longer BBs so that I could fit a pedal sensor. Different derailleurs have different reaches. I'm not sure which ones reach the furthest.

Whatever reach you have, it will be limited by the end-stop screw, so first you need to loosen that off to get the maximum reach for your present one.

The large difference in the number of teeth on your cainrings might not be a problem. You'll have to try it then let us know.

There's two potential problems I can see. Firstly, whether the chain will ride up from the small to the big sprocket. I think it'll probably work if everything is adjusted right, though it may be a bit slggish to change. Secondly, is the chain length. The difference in sprocket sizes needs to be taken up by rear derailleur, so you need quite a long one. You'll probably be OK if you ony use the small chainring with the low gears on the back, i.e. no min-maxing of the gears.