6 speed to 7 speed conversion

[flecc]

Mmmm, I wouldn't use those parts. I'm not at all confident that's a genuine Shimano rear mechanism. They show four genuine Shimano ones above, but that one is marked SIS, and SIS is not a Shimano range but a type of system invented by Shimano. It might be a cheap range made by them for low cost bikes, but I don't know of it.

The chain doesn't look too clever either when enlarged, the stamped plates far from flat. Showing it as that mixture of cassette speeds and system speeds indicates someone selling who hasn't a clue on bike part naming. They should work of course, but if poor quality it won't help.

My own megaranges run with Shimano Acera rear mechanisms and SRAM standard 7/8 speed chain.
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[Wizard9956]

Thanks Flecc , looks like i need to spend some more money doh , when i can afford it i'll buy a Acera derailleur , i actually bought the sis one because i thought it was made to match the Megarange cassette .

I see what you mean about the chain stamped links , they look bowed when viewed from above .

atb

Wizard

 

[flecc]

Right, just seen your photos. The chain doesn't seem wrapped round enough when on the small sprocket, it should start running forward more horizontally underneath the sprocket, I think that's why it's jumping.

Have a look at this quick snap below of my filthy Q bike and you'll see the chain wraps forward more, and that's on a 13 tooth sprocket. On an 11 it would be even more forward.

The problem you have is the spring inside the frame mounting boss of the mechanism isn't rotating the arm forward strongly enough, so the chain is pulling the mechanism too vertical and running the chain late into the sprocket.

There should be a circlip on the centre bolt of that so that you can get at the spring, and you might find adjustment holes to tighten the spring rotation more. It's a very fiddly job though.

P.S, Just seen your reply, and as you'll see, you might still get away with those parts.
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[Wizard9956]

Found the circlip , i'll have a go at getting the spring to give more lift tomorrow , and report back .

Thanks Flecc

atb

Wizard

 

[Wizard9956]

Hi Flecc , i took the derailleur apart today and moved the position of the spring on the upper pivot , i tried 3 different positions giving less spring tension , but although they all allowed the chain to wrap around the small sprocket better , each position caused the derailleur to clash when moving to the large sprocket ( 34 teeth ) . I'm going to have another look tomorrow and see if i can do anything else .
atb
Wizard

 

[flecc]

I've just had a very close look at your photos again. It's difficult to be certain with perspective distortion, but it looks to me as though the rear mechanism isn't moving out quite far enough for the 11 tooth sprocket. Viewed from the rear, it appears to lead the chain up and outward at a slight angle, and that would cause the inner chain plates on the outer edge to snag the teeth and cause it to ride up on the teeth. That would throw it up and make it jump.

If the mechanism can't be adjusted to get the alignment any further out, you'll need to add an additional washer on the spindle at the chain side to move the sprockets inwards from the frame just enough to get alignment. Then with the arm spring tension to suit, that should do the trick.
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[Wizard9956]

Hi Flecc , well been playing with my bike over the weekend and fingers crossed think it's sorted now ( time will tell ) , i've shortened the chain by another 2 links and managed to release a small amount of spring tension from the derailler upper pivot so the idller doesn't now clash when on the 34 tooth sprocket . Been for to short test rides and it hasn't jumped once .
Thanks for all your advice .
atb
Wizard

 

[flecc]

That's good Wizard. Some setups can be really stubborn to get right, and this seems to have been one of them. That's why Shimano et al make matched sets of components in ranges, since it irons out these problems.

Hopefully yours will behave now, and probably improve as the components bed in.
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