Incompatible rear derailleur?

[franz10mp]

Hi guys,

a friend of mine asked me to have a look at his bike because its chain falls off when he uses ‘soft’ gears. It is a 18 (6x3) speed mountain bike.

I understand that there is something wrong with his rear derailleur. When I put the chain on the inner wheel (the smallest) of the front chainwheel, the rear derailleur bends so that the chain rubs on itself. This must be the cause of the chain falling off. Note that all other gears work properly.

My first guess is that the rear derailleur is not compatible with a front triple chainwheel. However, before asking this friend to buy a new derailleur I would like some other opinions.

Do you think it is possible to find a solution to this mess without replacing the derailleur? What do you think the problem is?

Cheers,

Francesco

 

[Gatters]

Looks like the chain is too long to me might need two links taking out, have a look here for tutorial about chain length

http://www.parktool.com/blog/repair-help/chain-length-sizing#article-section-2

 

[Brandane]

Looks like the chain is too long and needs some links removed.

Edit .... As Gatters just typed!

 

[franz10mp]

Thanks for your quick reply. I'll have a go and let you know.

 

[Sheffield_Tiger]

Yep..chain too long as mentioned

Chain most likely comes off because it is too slack. as it looks to be all perfectly in line

 

[raleighnut]

Another vote for chain too long.

 

[Globalti]

Jeeze that bike really is a mess isn't it! For a start the rear derailleur cable is fraying and about to snap, which will leave him stuck in the smallest cog. The transmission is in a filthy condition.

 

[gbb]

Is the chain on the smallest cog at the front AND the smallest cog at the rear, that would give you the appearance of a slack chain. it will then give you the problem you're describing.

I cant tell from the photo....

 

[Heisenberg71]

Yep, looks like chain is too long and needs links out. However as above it looks like it's in small ring up front and small cog at back. This is not how any bike should be ridden and will unload the derailleur beyond its capacity (to take up the slack). Once beyond its capacity the chain will look like your pictures.

To be honest that bike is in sh1t state and the derailleur looks f***ed, the chain is probably quite stretched given it should be on Antiques Roadshow and the whole things needs sorting. If you want the easy option then whip some links out and send your mate on his way. If you want to do it properly then at least a new chain, cable and set up.

 

[franz10mp]

Thanks guys for your opinion, they are all very interesting.

I sorted the thing out by removing four links.

This friend told me that he does not want to spend money on this "£20 student bike" (his words), but he also told me that I can do it in March when he will get rid of it.

I think this is a good bike, a Giant. I have a similar one and it rides well. The fron derailleur on this firend's bike is missing, and as you say the rear derailleur with its cable look pretty bad. With no more than £30 I should fix it.

Do you have any reccomendation for a good value-for-money rear and front derailleur? What else would you buy to fix the bike?

Cheers

P.S. although the rear derailleur sucks, I can say that it now does its job properly after a little adjustment.

 

[Sheffield_Tiger]

The chain is on the 2nd to largest sprocket and the smallest chainring - the gearing is absolutely fine - there is no issue at all with the selected gear combination! Just shows that it's more than a couple of links want removing to be so slack in the selected gear - someone has obviously bought a new chain and fitted it straight out of the packet without matching for chain length with the old one

The chain isn't in best condition but a 3 x 6 is more forgiving than 9/10 speed setups, and a good clean and re-lube should see it work better than it has been doing, once the chain is shortened accordingly. I'm voting for it maybe not being all that worn (on guesswork from photos) because it's obviously newer than the rest of the set up due to the length, despite it being dirty. When you take it off, sit it in a plastic container and let it sit in a degreaser ideally - then clean off and re-lube

There doesn't look anything wrong with the mech to me other than being dirty, a missing "SHIMANO SIS" sticker isn't a performance issue and I see no reason to go splashing out unnecessarily

The cable..well, perhaps it should be replaced but cutting the frayed end back and crimping a cable end onto it or soldering the tip wouldn't hurt

 

[Gatters]

yep more than two links too long I can make out the chain isn't on the smallest rear cog from the pictures, I wouldn't rush into buying a new chain because it would need a new sprocket as well I would imagine next time the chain is replaced. If the rear mech is working leave it be, just fit a new (used) front mech if that's missing

 

[franz10mp]

Hi guys,

just to give you an update on this repair session!

After removing the four links everything seemed to be in proper working order. All gears were working properly. However, I fixed the bike upside down and did not try it.

When this friend came to pick the bike up, I could distinctively hear a clicking noise from the crank area whilst riding. So I flipped it over again for a check and the sound was gone. I started riding and the noise was there again. I can hear the noise while pedalling or coasting. It is quite paced: it occurs twice per revolution. So, I dismounted and tried to lift the bike from the back and pedalling using my hands. The noise was gone again. So it comes as I ride, probably it depends on the weight on the bike.

I have no idea what the heck it is!!!

The chain seems ok, and the gears are working well now. Do not know what to do. Any help would be much appreciated.

P.S. that friend was ok with the noise as far as he could ride the bike, but I wanted to fix the bike without side effects.

 

[Gatters]

could it be the plastic disk behind the sprockets...is it loose?

 

[franz10mp]

Unfortunately, I cannot check it now since the friend has taken his bike back. However, I can have another look next weekend.

In the meantime, if you want to suggest things to check I can create a check-up list. Plastic disk will be the first.

Thanks