Check my mech (please)

[si_c]

I think the reason for the b screw not appearing to be having an effect is that the pivot it acts on is too far from where it needs to be.

The mounting is a bit strange. The bit between the derailleur pivot and the hanger would usually be a claw mount, that would attach to the axle slot, with the pivot ending located over the hanger. In this particular case, though, the extension does not seem to have a claw, so the derailleur ends up too far from where it should be.

As I noted above the derailleur ends up exactly where it's designed to relative to the bolt hole - it's just not a mech that's generally expected to be used on an older steel road bike which generally has the hanger set to put the mech in the right place.

They are more often found on city bikes and the like with a single front ring and very wide rear range - the derailleur therefore sites back a bit further so that the sprockets don't foul the jockey wheels - this is the reason the Wolftooth road link exists. Functionally there is no problem with it being where it is, it just doesn't look right.

 

[Lovacott]

The gap here is about 14 mm. I have tried screwing the B tension screw in and out but it seems to make no difference at all to the angle of the pulleys.

Am I missing something obvious (in which case, educate me please) or does it look fine and I can stop overthinking it? Thanks all.

I have the same mech and had the same problem with the B screw seemingly doing nothing.

I slackened it right off but the gap wouldn't get any smaller.

The following weekend (after a week of commuting), I was cleaning the drive train and noticed the gap had closed up tight (to about 5mm) so I tightened the B screw a few turns to pull it back (widened the gap to about 10mm).

It now sits just right and I am having no issues.

Not sure why things happened this way but they did and that's all there is to it.

 

[RichardB]

That does look peculiar and it's odd that the B screw is not doing anything useful. If that is an RD-A070, however (?), then it looks like that in all the photos I've just seen, and since it has a maximum of 28 on the rear, as you have, but is designed for a triple front, perhaps things look more normal with different chainring sizes, other than your single 44.

It is indeed an RD-A070. I didn't know it was designed for a triple front, but given the length of the arm that makes sense.

It's a Tourney derailleur so they have that extra swing arm on them - they are designed to cope with a very wide range of sprockets at the back and it helps give the derailleur additional room to clear the larger ones. Mrs C has exactly the same setup on her town bike but that has a 14-34t megarange freewheel on it.

The older steel frames were designed around having a short cage traditional mech fitted, the setup you have there will work without any problems though.

Thanks for this. I knew I was going to end up with a fairly wide-ratio block (hilly area), so I avoided the short cage options. As long as it works, that will be fine. I was just curious. So many floods round here today I don't know what route will be available to me to get to work tomorrow - so any bike testing will have to wait!

 

[RichardB]

Not sure why things happened this way but they did and that's all there is to it.

At least I am not alone

Thanks to everyone who responded - learned a bit today, cheers.

 

[Ajax Bay]

This is a stock image (below). I note that the arm that @YB thought might be a wolflink appears to be at a different angle but think the angle it sits at will be determined by the extent to which the mech is 'pulled' against its spring. @Lovacott 's experinece suggests the pivot (2cm below the fixing screw)might often be stiff. Is it Richard? I haven't got this model of Tourney to check, but oiling and simultaneous oiling might loosen to useful effect.

 

[RichardB]

This is a stock image (below). I note that the arm that @YB thought might be a wolflink appears to be at a different angle but think the angle it sits at will be determined by the extent to which the mech is 'pulled' against its spring. @Lovacott 's experinece suggests the pivot (2cm below the fixing screw)might often be stiff. Is it Richard? I haven't got this model of Tourney to check, but oiling and simultaneous oiling might loosen to useful effect.
View attachment 563919

The mechanism swings smoothly to its limits under hand pressure, so I don't think a stiff pivot is the problem. The B screw doesn't feel as if it's bearing on anything, just turning in fresh air. I think I might put a few links back in the chain and see if relaxing the chain tension helps it sit a bit closer.

Will report back, but it will be a few days now as I have a block of shifts to do.

Thanks again all.

Cheers all.

 

[T4tomo]

I dont think you needs to add any links, you have about as much movement of deraiileur forward from vertical one largest cog as you do backwards on smallest cog, and changing is normally better with a slightly shorter than longer chain. you just have a rear deraiileur with a large capacity ("modern" triple when running a low capacity set-up of a single and 14-28 block

 

[RichardB]

I dont think you needs to add any links, you have about as much movement of deraiileur forward from vertical one largest cog as you do backwards on smallest cog, and changing is normally better with a slightly shorter than longer chain. you just have a rear deraiileur with a large capacity ("modern" triple when running a low capacity set-up of a single and 14-28 block

... is, I think, the right answer!

Cheers.

 

[Cycleops]

Just have a beer and ride it, not necessarily in that order

 

[Lovacott]

@Lovacott 's experinece suggests the pivot (2cm below the fixing screw)might often be stiff. Is it Richard? I haven't got this model of Tourney to check, but oiling and simultaneous oiling might loosen to useful effect.

TBH, I had never even bothered with the B Tension screw until I watched a Park Tool YouTube on indexing and it was mentioned.

I took a look, noticed the gap was bigger than recommended and slackened off the screw. The mech didn't move. However, the mech moved nicely back and forth with very light pinky pressure (although the spring seemed a little feeble).

Even without the chain fitted, the mech would not move any closer (like the spring didn't have enough "spring" to push it forwards?).

But after about a week of riding with the B screw almost fully out, the mech had moved in on its own (as if by magic). I then adjusted the B screw inwards a bit until the mech began to move slightly out and then stopped my adjustment.

Right now, everything is as it should be.

One possible theory is that the spring had been stressed by its position and needed a week or so to find its original shape? FIIK?

I'm not exactly sure if the B screw adjusts spring tension or whether it is a limit stop? (I'm not about to strip it down to find out when it doesn't seem to be causing me any problems).

Any knowledge of the inner workings of the tension spring and screw would be gratefully received.

 

[simongt]

Cor, haven't seen a five speed in a while - ! Nice - !

 

[RichardB]

Thanks all. I'm going to ride it for a while and see how it goes. As I said previously, I've no reason to think anything will be wrong, just curious about the pulley/sprocket alignment and the non-functioning of the B screw. When this bloody rain stops ... (Normal route to work flooded and impassable today, took me twice as long.)