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)
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.