I’ve got a bit of play in the needle bearings in my Lefty.
It makes the bike a bit odd to ride, as it’s a bit like a loose headset, in that it move back and forth, and it rotates a bit as well.

Looking at replacement bearings on Qwerty, there’s various thicknesses of inner and outer races available.
http://qwertycycles.co.uk/products/cannondale-inner-race-for-lefty-headshock
http://qwertycycles.co.uk/products/cannondale-needle-bearings-set-for-headshock-and-lefty-forks-hd161
http://qwertycycles.co.uk/collections/lefty_parts/products/cannondale-outer-race-for-lefty-headshock

First of all, I don’t understand the numbers.
I take it the second part of each number is the thickness in inches; 0.021, 0.024, 0.025 etc.
So what’s the first part; 5.25, 5.425, 5.665 etc. ?

Secondly, how do I know which ones I have got, is the part number marked on them ?
Should I just get the same ones, or might I need some slightly thicker ones to allow for wear ?

Thirdly, they are sold in packs of four of the same size, yet there is a warning that I may need two or three different sizes.
At £20 a pack, this could get expensive.

Does anyone replace these bearings themselves, or is it best to go to a Cannondale dealer where they hold a stock of bearings and can select the best fit ?

I would not do either of mine myself and send them to TF Tuned if they needed doing.

is it best to go to a Cannondale dealer where they hold a stock of bearings and can select the best fit ?

Not every Cannondale dealer can do fork servicing. Needs to go somewhere that does it, e.g. the confusingly-named Leisure Lakes Nottingham (which is in Derby).

While I cannot offer much advice regarding your choice of bearings, I can tell you that it is a really fiddle job to do. I bought a Lefty from here and decided to strip and re-grease and re-seal the fork.

There are plenty of guides on the the net that will show you what to do using step by step photos and descriptions however it is still a time consuming job to do, (it took me five times to put the two halves of the fork together ensuring everything was in the right place).

I used Dr.Cannondale for all my parts give them and Qwerty a call with a model number as they may be able to help with bearing selection. Dr.Cannondale were spot on for all my parts with a delivery time of less than a week.

I haven’t stripped the fork yet, so I don’t know which parts are worn.
If it’s just the needle rollers then it’s pretty straight forward.
If it is the races, then it’s looking like a trip to a dealer.
I assumed any Cannondale dealer would have the tools, parts and experience to service a Lefty. Looks like I’ll have to phone round tomorrow to see if any of the local ones can do it.

I don’t know why, but I’ve got an idea Qwerty are near me in Worcestershire. There’s no address on their web site.
There’s no mention of servicing either, so maybe they do just sell parts.

Give Mike at Revel Outdoors Bury St Edmunds a call, what he doesn’t know about Leftys isn’t worth knowing. They’re part of cannondalespares dot com too so can mail order you any parts you’ll need.

Or give Tony a call at Thumprint Tuning, he is Mr Lefty!

I had my last service done at Noahs Ark. Full bearing replacement at a very reasonable cost. I believe the races in your fork will be marked with the size required. Not ideal, it should be marked on the fork really!

By the way, qwerty don’t service but Lloyd and Rachel should be able to advise. Drop them a mail.