Cause of clicking jockey wheel?

[JimN]

New chain, new cassette, and new jockey wheels as all were completely worn. The gear indexing seems fine but I can't get rid of the regular (every six links or so) missing beat as the derailleur moves forward and then clicks back. Is this normal until the jockey wheels settle down? Can't say that replacing jockey wheels is a regular feature of my cycling life - they have always seemed to last for ages.

[Kim]

You have got the jockey wheels the right way round, haven't you?  The upper one should have a bushing with some horizontal play.

[BFC]

Some (many) jockey wheels are fussy about position in the mech and direction of rotation.

Take the rear mech cage apart (again!) and put your best reading glasses on, look for any direction arrows and upper (or guide, top) and lower (or tension, bottom). They often only write on one pulley or side! Then work out which way the pulleys turn when in use...

The lower jockey wheel is designed to take the chain in from a wide range of angles and center it for the upper pulley, the teeth can be shallow and narrow or can be wedge shaped to accommodate the wide range of input angle.
The upper pulley is designed to feed the chain onto the cassette and will have taller straight teeth that will force a gear change, often there is side float on this pulley to allow for near silent operation once changed - this allows for the curved motion of the rear mech not giving a perfect indexing.

Designs and markings vary by manufacturer and model, then there are generic service kits. If you know what to look for you can spot the markings, worse when servicing an old set burried under thick transmission shite.

[mrcharly-YHT]

I had this problem once. I'd fitted the wrong jockey wheels. The teeth were riding up on the chain link after x rotations.

[JimN]

Thanks all, apologies for the delay in response - a very busy week and have not had a chance to login. I will have a look tonight .... I thought they were identical. Live and learn!

[JimN]

"Best reading glasses" is dead right. Without them I still couldn't see the difference, but changed them round anyway ... and WHAT a difference. So I had a really, really close look. And yes, in tiny, tiny writing on the lower wheel, there it is.  Been around bikes for years and still learning the basics

[quixoticgeek]

"Best reading glasses" is dead right. Without them I still couldn't see the difference, but changed them round anyway ... and WHAT a difference. So I had a really, really close look. And yes, in tiny, tiny writing on the lower wheel, there it is.  Been around bikes for years and still learning the basics

There are two types of bike mechanic. Those who have made this mistake, and those who will make this mistake...

J