Front derailleur woes

[belgiangoth]

In the midst of swapping shifters and cables. To be fair the second hand bike never shifted well into top gear at the front. From the looks of things even with the H limit screw fully loosened and the B limit screw totally tightened the whole thing sits too far towards the frame. My guess is that it's the wrong model for the bike, but then again I haven't ever had a bike with a front derailleur. Is there something in the setup that I have missed (which might explain why I see little effect when I'm changing the limit screws)?

[Brucey]

photo?

[willcee]

A pic or 3 would assist the issue.. check the cable is tight enough so that its not taking lost motion before moving to pull up the meck onto the big ring..easily done , so check when its on the small ring that its quite taut at the down tube.. will

[belgiangoth]

I shall mess about with photos tomorrow ...

I have got it working but I have to hold the derailleur out and then attache the cable under tension to set it on the lowest gear. I would have thought/I read that I should just be able to set limit screws to set it up without the cable attached.

[peetee]

Sounds like the crankset is too far outboard. You say you have never run a bike with a front mech, does this bike have a mix and match crankset and bottom bracket?

[belgiangoth]

Yeah, sounds about right. It’s second hand, a recumbent. I can get it to change gears through all gears but
1. Both limit screws are maxed out (b in, h out).
2. I have to put more tension in the cable to set it up, basically I stuck a book between the derailleur and the frame to hold it in place on low gear while I tensioned the cable.
3. Gear shifter is a bit clunky, will drop from top to bottom and sticks a bit. Could just be a shifter issue, or could be linked to too much tension in the cable?

[belgiangoth]

Front, in top gear

and in bottom gear

I realise I will not be winning any prizes for photography...

[9494arnold]

Hard to be 100% sure from your photos but I think that the derailleur cage isn't parralell with the chainrings .
Which will have the broad effect that it'll change easily onto the little ring but the cage will be touching the inside of the crank before it moves far enough out to engage with the big ring . It may also be creating the maxed out adjuster screw scenario.

[belgiangoth]

Already tried that, but good thought.

[Norman H]

Is it a square taper/sealed cartridge type BB?

There looks to be enough clearance between the chainrings and the frame to allow the fitting of a shorter BB spindle.

Failing that the front changer appears to be shimmed to fit the frame tube. There may be some scope for fitting an eccentric shim.

Also worth checking the height of the front mech.

[peetee]

Looks like there is slack in the cable with the chain on the small chainring. To set the cable up get the chain on the small chainring and the large gear sprocket, undo the cable and adjust the inner limit screw so the inner cage plate clears the chain by 2-3mm. Put the shifter into first and pull the cable tight and do up the retaining bolt. Shift the chain up and down the chainrings and sprockets to check the clearance of the top limit screw.

[belgiangoth]

I agree Norman, I think a different BB is the obvious solution. I have checked the height of the mech, any lower and it will hit the middle ring in shifting.
Clear instructions for me there peetee, but if I disconnect the cable and fully screw in the B limit screw the mech still sits on the inbound limit of the lower chainring.

[Brucey]

I agree with Norman too. Basically with a 'road triple' the innermost chainring should be in danger of obscuring your view of the end of the BB shell. The chainline to the middle chainring ought to be around 47mm (from the bike centreline).

If you depart much from this (outwards) then a 'road triple' FD will often struggle to reach out far enough for the big ring and it may (as you have discovered) be impossible to set the inner limit screw.

As well as a shorter BB spindle, you could perhaps also solve this by using an MTB FD; these are designed to run a wider chainline. This will only work well if you are using an MTB shifter or non-indexed front shifting.

BTW there are a whole bunch of other reasons why an FD won't work very well, which are related to the FD design in relation to the chainset setup. On a recumbent there are additional issues which relate to the angle the chain runs through the FD when viewed from the side.

cheers

[belgiangoth]

Cheers Brucey,
I had assumed that it would be a MTB, as a bigger difference in chainrings would be wanted which == MTB (I thought).

[Brucey]

do check the model number but I think that is a 'road' FD, from the look of it. What shifters are you using?

BTW 'road' triple mechs are most commonly used on recumbents because they have the biggest capacity; there are some which will manage ~28T (eg 24T to 52T) on a solo. On a recumbent the capacity can be larger (if the mounting position is correct in relation to the chain run) because the chain run doesn't vary in angle (wrt the horizontal) as you shift gears at the rear.

cheers