Hello all

Just bought my son a second hand malvern star, it's 20" and has 6 gears.

I'm trying to align the gears as they are not working properly. I have two problems:

1. When changing from 1 to 2 the chain doesn't move correctly into place and keeps rattling on the second sprocket. So I have adjusted the tension and it moved into place just fine. Quick check, gears 1 then 2, back to 1 and 2 again and it's moving beautifully. Now I have the same problem between gears 3 and 4. So I have adjusted the tension just like before, check again and it's perfect! But ... by fixing gears 3/4 I have actually messed up gears 1/2! If I fix 1/2 then 3/4 get messed up. What am I doing wrong???

2. Other problem occurs on the sixth gear only (larger sprocket). It seems the little pully sprocket (I hope that's the name) sits right on top of the gear sprocket and they are touching. Does that mean the spring is ruined?

I hope this makes sense, it's a bit hard to explain this all in writing.

Many thanks in advance...

Hope this tutorial helps you.

Align ? above is a picture of stroke limit screws, so only time you bother them
is if the chain jumps past the edge cog,

I expect the bike has been tossed on the ground on the right side, and stuff git bent

NB: the dropout hanger needs to be in a parallel plane, up/down, front/back,
to the wheel/freewheel.

Bike shops have a tool that goes on the hanger, if it is part of the frame.
the other way the most basic parts are made , it's part of the rear derailleur.
then, you will just have to cope with 'the huffy wrench'.. vice-grips adjustable spanner, etc.
and un bend things.

The post is a video, not a still pic! It actually does a pretty good job, including discussion of the importance of alignment of the derailleur to the wheel/frame.

Kids throw their bikes down is the Given.

Thus, IGH FTW.

Thanks everyone for the replies.

I watched this video already and many more on the web. I wish this guy challenged himself a bit more by showing how to do gear maintenance on some old bike, not a brand new one where the gear is sparking new!

Anyhow, my problem is not with the limiting screws as it is with the middle range gears. I have managed to play a bit more with the tension cable and it seems to be working slightly better. Not perfect, but perhaps I think at some point I might just replace the cable and the housing and see if that helps. Problem #2 still stands, where the little flywheel seems to be sitting right on top of the 5th and 6th sprockets. I have marked this with the two arrows in the image below:



Any idea on how to fix this?

Thanks again!

Looks like the problem is not the limit screws which control the lateral motion (so that the chain doesn't fall off on either side of the cassette). What you need to adjust in this case is the b-tension screw. The b-tension screw adjust how close the chain pulley is wrt largest cassette. Here is the link to sheldon's description:

https://sheldonbrown.com/derailer-adjustment.html

Here is one on Park Tool's website with more pictures. See section on b-screw adjustment..

https://www.parktool.com/blog/repair-...nts-derailleur

If an old derailleur is in proper alignment and not terribly worn the adjustment procedure is the same. One has to start with the way things are supposed to be in order to spot what is different.

First - the middle gear problem. It's a good idea to make sure the cable and housing are proper, but the most common reason for inconsistent shifting is a problem with rear derailleur alignment - not just bent inward but possibly twisted.

Second - the rubbing of the derailleur pulley on the large rear cog. Yes it could be the spring, or the chain could be the wrong length, or it could be a replacement derailleur that is not a good match for the freewheel. I don't think that derailleur has a b-tension screw.

It's at least as hard to diagnose remotely as it is to explain in writing, or even with pictures. A mechanic looks over a problem from multiple angles, also using sound and feel, considering not only one part but all the parts that interact with it. At this point if you have watched multiple videos and understand and followed them you should have all the info you need for routine adjustments. That means it's not routine or you are not going to fix it as it sits.

The odds are good that a new derailleur will solve the problem, though I certainly can't guarantee that. Installing a new derailleur is not that challenging incrementally over adjustment, as long as you get one that is compatible with the freewheel. I would suggest you abandon trying to get that one to work.

Thanks grasse, but .. could it be that there is no b-tension screw on this gear system? I looked before and could not find anything adjustable except for the hi/lo screws and the tension pulley. Any chance the b-tension screw is under the black plastic covers? I tried lifting them but was afraid they might break.

Also, anyway of knowing what type of Shimano gear this is? Wishful thinking - but perhaps I could find a user manual on the web...

Thanks for that bikeman!

I think you're right because as I mentioned before I have already looked everywhere and could not find anything adjustable except for the hi/lo screws and the pulley.

How do I know what is a compatible derailleur?
Please please don't send me to the shop, I'm an avid DIYer and I really enjoy the challenge and learning experience. If possible I would even attempt at taking the derailleur apart and replacing the spring alone.

One way to fix this is to shorten the chain, that will change the angle of the RD cage as it takes up the slack in those gears. Be careful though, make sure you can get into big big before you shorten too much.

Looking at the image you posted, maybe you can loosen the axle nut and rotate the entire derailleur clock-wise and then tightening it down. You need to somehow rotate it to the point where the cage is clear of the largest cog. That's what the b-screw is suppose to do with derailleur that is bolted to the frame via a hanger.

These are cheap and have a B screw-

https://www.bicyclebuys.com/drivetrai...Fe9xQgodAAIAdQ