I've just change the freewheel for a 34T and I also changed my rear derailleur for a Tourney 7sp (i run friction shifters).

I would like to have a bit more distance between the cogs and the derailleur. But I cannot. What am I doing wrong? Or are there any trix?

34T freewheel with Tourney derailleur Closeup B tension screw maxed out

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    nice depth of field in the 2nd pic (macro photo?) – amonk Jun 28 '17 at 16:13
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    @amonk its a 25f0.95 on micro four thirds. – Ola Jun 28 '17 at 17:58
  • I've been riding it for a while now and it works fine. – Ola Feb 20 at 18:19

That's just what the combination of the 34T rear cog and Tourney derailleur looks like. Here's mine, using the 38T chainring:

enter image description here

Using the 28T chainring doesn't move the top derailleur pulley any farther from the cog, so using a longer chain won't make any difference.

It doesn't seem to cause any problems for me, though I don't use the 34T rear cog very often: it's too much of a jump in gear ratios from the next one down, which is a 24T.

However, I don't have the same model of Tourney derailleur as you. Your derailleur looks like the RD-A070 and Shimano's compatibility listings indicate that this is only compatible with freewheels whose largest cog is a 28T.

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    I myself really think the 34T is a great feature. When it's a harder hill it's nice to be able to get really low geared. Especially with a kid on the back and some picnic on the rack :) – Ola Jun 28 '17 at 11:17
  • I've been thinking of going with 34T myself. I currently have front 48-38-28 and rear 24-...-14, which is fine on flats but I live on hills, and (I see now) I really should have had mountain gearing from day one, which mine is not. – compton Jun 28 '17 at 13:56
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    @compton It depends on how you use the gears. If you regularly find yourself needing a gear lower than 28/24 then go for it. In my area, 38/24 is fine for most of the hills and, when it isn't, I'd much rather drop down to the small chainring at the front and use 28/14-24. The problem comes when I think I can tackle a hill on my middle chainring but misjudge it slightly. If I can't get up at 38/24, my only options are to use the front derailleur under load or change to 38/34, which is a huge jump in ratio. I'd much prefer to be able to go to something like 38/26 or 38/28 instead. – David Richerby Jun 28 '17 at 14:15
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    @compton Do you mean small chainring and big rear? Small chainring and small rear gives you the same sort of gear ratios as middle chainring and middle rear: 28/14 is roughly the same as 38/18 or 38/20 (it's actually 38/19). – David Richerby Jun 28 '17 at 22:21
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    @DavidRicherby And yesterday was my day ... – compton Jun 29 '17 at 17:07

Try tweaking the B tension screw. It is very likely the big shiny silver combo pilips/flathead in your third picture.

As you tighten the screw it should increase pressure on the internal spring. making the upper jockey wheel further forward.

Slackening the screw a bit should relax the spring and allow the chain to pull it toward the back, and therefore further from the big cog.

Get your bike up on a stand or hang it from some ropes and give it a try.

You might be able to get some more clearance by replacing the top jockey wheel with a smaller one.

Yours appears to be a 14 tooth in the picture. Jockey wheels are available from 10 tooth to 15 tooth.

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    I've got this exact problem on my folder, which is a 32 tooth big gear. Turns out its possible for the top jockey wheel to clip over to the wheel side of the large cog and stay there until I get off and help it shift back down by hand. Not ideal! – Criggie Jun 28 '17 at 10:22
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    Thanks! To replace the top jockey wheel is a smart idea! I'll try that first. Think I have some wheels lying around :) – Ola Jun 28 '17 at 10:58
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    I tried to change the jockey wheel but strangely it didn't help. – Ola Jun 30 '17 at 16:23

It's not completely solved yet but I think it will work now. I tightened the b tension screw as much as I could and now it doesn't touch the 34t cogs any more. I'll ride with it a month to see if it worked itself out or not.

Thanks for all help and good suggestions!

Update after 2 weeks: It seems to work fine.

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