Chain tension woes

[fjpshaw]

Cheers guys. Yep, long cage mech already fitted.

Weather held out today so was out for a couple hours - it happened again, but not as often. Question: if the front mech was aligned so that it shifted on to the outer with ease (which mine doesn't - as I've said above), would it help stop the chain from jumping down chainrings? My thinking is that with correct alignment/setup, once the chain is shifted, the two plates of the mech would be more or less central to the running line of the chain, and the left hand plate (as seen at from rider's perspective) would give protection from jumping down a ring - i.e. to the left. Whereas with mine just now, you could drive a bus through the gap between the chain and the left plate when on the outer ring.

 

[mattr]

That's the theory, yes. the front mech acts like a moveable chain guide.

 

[RobMac]

Set up to length using the standard 'big ring to big ring' method

Where did you get that from? Have you ever read those Shimano instructions that come with their components?

 

[fjpshaw]

Set up to length using the standard 'big ring to big ring' method

Where did you get that from? Have you ever read those Shimano instructions that come with their components?

Real men don't read instructions.

Run the chain round the outer chainring, then round the large sprocket (ignoring rear mech), then rejoin the chain. It's how it's been done for centuries!

 

[clubby]

Run the chain round the outer chainring, then round the large sprocket (ignoring rear mech), then rejoin the chain. It's how it's been done for centuries!

You forgot the add 2 links part!

 

[jimo746]

if there's a mahoosive gap for the chain to slip down to the middle ring, then odds are it WILL happen. Try adjusting the front mech, wind some more tension onto the cable, and check the upper limit screw .

 

[fjpshaw]

Re:

if there's a mahoosive gap for the chain to slip down to the middle ring, then odds are it WILL happen. Try adjusting the front mech, wind some more tension onto the cable, and check the upper limit screw .

Cheers Jimo. Wasn't 100% whether the derry acted as a guide as mattr suggested, or whether once it has shifted the chain, it just sits there waiting for the next shift.

Re further adjustment, the mech is already at full reach - any further and I'll be taking chunks out my ankle. And High/upper limit screw is probably only being held in place by a quarter turn ! So I think all eyes have to be on the BB at the mo.

 

[gmac123]

sounds like the BB to me

+1 on the add 2 links

had a similar problem when I first my my zaskar, chain line looked ok(ish), however the BB was too wide for the front mech and had to be changed for a smaller/more narrow BB.

it struggled to reach the outer ring (but did, just) and more importantly retain the chain on the middle ring. until this incident I didn't realise how much work the front mech was actually doing on the chain retention front.

on the rear, the B tension purpose is to set the distance between the top jockey and sprockets with the aim being as close as possible to aid slick shifting, without interference

these things are sent to try us, and they do!

GL