The Facts :

New connex 9 speed chain
Fairly new SRAM PG 990 9 speed block
New long cage and jockey wheels on XO rear derailleur
X9 fhifters – not so new but still going strong.
New BB (just so you have all the changes)

Fitted everything the other day and in all but the smallest cog on the back everything is fine and dandy – near silent – including under load.

On the smallest cog the chain skips ! FWIW I don’t spend massive amounts of time in the 11 tooth sprocket.

After forensic research I can say categorically that it is not :

a. Riding up on the next cog
b. Has no stiff links

It is :

a. Is the correct chain for the set up
b. Riding up on the teeth of the small cog (on the bearing not the side plates) – at the connex quick link, just after it leaves the upper jockey wheel (which is perfectly centred over the sprocket)

Conclusions :

a. The quick link is too small – I have checked that the 2 pieces seat together correctly – they do. I have also tried a different quick link same result.

b. The teeth on the small cog are further apart than they should be – wear – except all other links slide in beautifully.

What the chuff is going on ?

Help before I go all Basil Fawlty and start beating the bike with a branch regarding the warnings I’ve given it.

If the problem is only on the smallest gear then maybe the limit screw isn’t quite set right, or something else is stopping the mech centring on the sprocket.

If only. The mech is bequtifully centred on all sprockets.

I can actually see the bearing start to ride up on the tooth causing the next link in the chain to lift and effectively shorten so it soo rides up – even more. Eventually it gets to the point where everything slips down into the next…er…what the oposite of the tooth….valley / dip ?

The cassette is worn.

Seriously ?

On only one cog and for only 1 link ?

Yep, worn cassette. Wear manifests itself worse as the sprockets get smaller – less margin for error when the chain is curved tightly.

I never put a new chain on a worn cassette. Change both at the same time.

What do you mean by the “bearing”? there are no bearings in chains.

Do you mean the rollers?

Hmm. Weird, if it’s only doing it on the joining link. Get another quick link, they’re cheap and it’s useful to have spares. Even an old SRAM one or whatever should work for debugging purposes. Stick that in instead of the Connex one, if it fixes it there’s your problem. If it doesn’t then it probably is a worn cassette.

just replace the smallest cog. You can buy replacement XT cogs for about £4 each and change the smallest 4 for much less than a new cassette.

the rollers are bearings as they spin

Plyphon yes I mean the rollers.

Rob Jackson that was what I thought.

Monkey P – cracking idea

All – ta for that, very helpful and saves me cleaning twigs and leaves out of the bikes nether reigons.

Monkeyp – will XT cogs go on a SRAM block ?

Bugger it. New block from Planet-X for £44.99 on order.

the rollers are bearings as they spin

Nope, they’re rollers.

rollers are bearings by definition surely! “moving part or for free rotation around a fixed axis”

But a bearing by definition is separated by moving “bearings” – hence the name. 🙂

(or their roller format)

A bearing is manufactured to be tight and precise, a roller on a chain is (by comparison) only roughly round and is loose to flop about over the grime.

I mean, I’m being totally pedantic, but it might help you get a conversation started faster one day explaining how the rollers of your chain are slipping over the teeth rather than explaining to a confused mechanic where the bearings are in your chain. 🙂

I would have called them rollers but they’re still a bearing.
I work with a steam turbine where each bearing carries over 10 tonnes but they don’t have balls or rollers, just metal on metal and lots of oil.

i win

I had similar, fixed by removing the quick-link jobby any refitting it the other way up…

Or just join the chain the old-fashioned way and don’t use a quick link?

And the old fashioned way is ….?

the quick link on the connex chains is directional, make sure you have it on the correct way or it will jump on the small cog!

its called reading the instructions, its helps when things dont work the first time.

link to instructions

I’d have lived with it for the sake of £45…especially seeing as you don’t use that cog!

They’re not bearings or rollers, they’re pins, surely?

I N R A T S but I’d say worn 11T sprocket, incorrect B-tension or just “one of those things” – I’ve seen the same on all-new parts!

Take it back to the shop, explain, and get it sorted.

As above worn cassette

Don’t worry about it, chain will wear after 5-10 rides and it will stop skipping

They’re not bearings or rollers, they’re pins, surely?

Yup correct, they’re pins with a roller over the top.

Trevorflint82 – Really ? the thought never crossed my mind. They look identical to me. Doh !

Will advise results.

Edit – having looked at instructions there doesn’t appear to be any thing to say they’re directional. I’ll try it anyway.

Can someone just clear something up… The up/down limit screws only affect the up/down limit? Or does it affect the whole alignment on the entire block? I may have just misread, or, found a fact I didn’t know about setting up rear mechs!

To put it basically, the L screw sets up 1st gear and stops chain falling into the spokes, H screw sets up the top gear and stops the chain falling off the cassette.

The B screw is for sorting the gap when in top gear and the top jockey wheel to make sure the chain has enough clearance, if you get my drift….

Trevorflint82 you are a chuffing GENIUS.

Everything works beautifully.

Wish I wasn’t so impatient. I now have a spare new cassette. Oh well, perhaps I deserve a spare set of wheels ?