Hi,
I'm having some re-occurring issues with my LOOK 675 headset. This vintage is the kind that screws on using a ring at the top of the head tube and then gets set in place using a dowel through the ring itself. See you tube video for more details on set-up:

I've had no success is achieving a snug fit on the headset that lasts. On at least 4 occasions I have popped off the stem and rubber washer so that I could tighten the ring good and snug before reinstalling and confirming 0-play. Within 200km...the fore-aft play is back.


I then contacted my local LOOK rep who suggested a dab of Locktite on the ring before re-installing. That seemed to work for a longer period of time but the play is back...and of course now with the Locktite on there I've gone and bent the adjustment tool trying to re-adjust...nice.


My next step is to take a hammer and pin to the ring and force it off and re-apply locktite and well, tighten the thing even harder but I'm concerned that the headset will no longer move smoothly.


Before I go and do that, I was just wondering if anyone else has encountered this issue...also wondering if anyone things that replacing the bearings themselves may help (my guess was no...).


Also very slightly worried that the play is actually caused by the built in bottom cup being a sliver too wide...

Not sure if this is helpful, but every time I've encountered a headset that wouldn't stay tight, it was because I wasn't tightening it enough to begin with. Cartridge bearings can stand a lot more preload than loose balls. And it seems, based on my experience, that tightening just until all the play is gone, as I had always done with loose balls, really leaves a tiny amount of play that eventually increases.

So I'd recommend cranking down on the adjustment ring either until you feel the bearings start to bind or until you feel like you should stop. Hopefully that does the trick. A little heat (perhaps from a hair dryer, anything more intense could damage the frame) should help loosen the Loctite you applied so long as you didn't make the mistake of using a high strength version.

Thank you, Joejack...I will keep this in mind when I give it another manhandling! Good idea re: hairdryer!
Edit: just tried getting it apart with the hairdryer...worked like a charm. Thank you!

Did you ever manage to fix this ?

I've got a loose headset on my 2014 Look 675 - the one with the A-stem.
I just can't seem to get it tight enough and braking on downhill runs is a scary experience.

I believe Look engineers started dropping too much acid with their later designs. Look has screwed the pooch before with beyond horrid proprietary seat posts but that headset design is a disaster. I owned an early Look bike which was great but in their design arrogance, they had to be different and in doing so, ruined the product line.
This is my opinion and Good luck.

I've got a 2011 Look 566, and have been dreaming about the later Looks - now I'm having second thoughts. There are no Look dealers anywhere near me. Something like what you're going through would really suck.

I'm beginning to think that headset might be flawed in design
My bike is 4 years old now and the dealer I purchased from is 2000 miles away.
I'm tempted to remove the threaded insert, the pin and the locking ring, and replace the compression plug with a better one to see if I can get a tighter fit.

You won't get anywhere going with a different compression plug. The plug on this design is almost redundant. All it does is pull the stem against the frame. It is NOT used to manage the tightness of the bearing assembly. The lynchpin of this design (pun intended) is the screw-on ring and the pin. The degree to which you tighten the screw-on ring is what determines the tightness of the bearing assembly.
As such, I think you are stuck with the proprietary parts unless you want to switch out the stem and go with a regular set-up altogether which would look ridiculous.
Do not be tempted to overtighten the threaded ring. If you start bending the two-pin tool, you have overtightened. My thinking is that overtightening then puts too much pressure on the surface where the aluminum cup sits in the carbon top tube (well aluminum in the case of the older 675's anyway) and you will be more prone to cracking the carbon.
The Look rep here in Canada suggested putting a dab of loktite (blue not red) on the threading to help keep it in place. This did help things when I did it (it doubled the mileage before the thing got loose again) but it made it difficult to take the assembly apart again (you had to heat up with a hair-dryer).
As I said previously, still love my Look 675 but that headset design needed a few more test cycles before it reached market. I wonder whether any of the rider who took this on Paris Roubaix experienced the same kind of looseness.