[Closed] Having to tighten down top cap a lot

First thing (apologies if this is egg sucking...) you are loosening the stem before you tighten the top cap, yeah?

If so, I'd guess you don't have enough spacers below the top cap or stem. Take the top cap off with the stem still tight and see how much gap there is between the two of the stem and the end of the steerer. Needs to be a good few mm. Sorted a fair number of bikes where this is the issue.

replace the bearings - if it's cartridge bearings it's an easy job. If they're loose (or in a holder), check the bearing races, if they're damaged then it might be time for a new headset.

If not the above the bearings may be squashed and knackered by over tightening

Checked the steerer bung is secure?

Has this always been the case from new, or has something changed/happened that coincides with the play in the headset?

Could the play be fork bushings/hub/caliper/pads?

Yes, overtightening will potentially shorten the life of the bearings.

Have you checked the condition of the bearings? They're only a light press fit so you should be able to remove them by hand and check whether they are graunchy or have play. If so, you may get away with regreasing them temporarily but your best bet is to replace them. Take the oppportunity to clean any grit etc. out of the headset cups and crown race and regrease them.

You can use the method @ 1:15 to try and determine whether it is the upper or lower bearing which is causing the issue.

This can be the conical spacer / bearing interface not allowing the play to be taken out. I've had it on 3 bikes where the top of the head tube has obviously been machined before painting and the paint thickness stops the conical spacer being able to tighten down onto the reducer for the bearing properly. If it has a spring type reducer it can feel fine on a stand then the play be apparent when riding.

Usually it has come about when replaced OE bearings and the minute tolerance makes a difference, or where a new bike has had the bearing seats packed with grease and after a very short ride it all starts moving.

If it is this then two solutions - skim top of head tube to clear paint or insert a micro spacer under the conical spacer. I'd do the latter first, FSA do packs of them for a a variety of steerer diameters. If that solves it you can leave as is or skim.

Assuming its not user error as submarined said.

I had a frame that wouldn't stay correctly adjusted. Turned out to be the stem was machined slightly squiff so it didn't load the headset evenly. But that would be evident from day 1.

A bent steerer tube has the same symptoms though.

If all else (correct spacers etc.) then check to see if it needs a shim ...many headsets actually come with shims.

as per boombang, lots of these for different sizes or check if the bearing is correct (thickness)

I’d guess you don’t have enough spacers below the top cap or stem

Yep, I had to put a spacer of about 1-2mm height to get mine sorted.

A bent steerer tube has the same symptoms though.
Also, worse case, stretched headtube. Can happen from running headset too loose

Cheers, lots of replies/info.

The bike has always been like it, I bought the frame (planetx fully monty sl) and this headset:
https://www.wiggle.co.uk/brand-x-headset-integrated-tapered-steerer

I did cut the steerer down myself but pretty sure the spacers are ok - steerer sits probably 5mm below the highest spacer.

Is the starnut creeping up the steerer tube by any chance?

Is the headset cover bottoming out on the frame before the play is taken out? If it is, you need one or two of those wafer thin shims underneath it.

I had a problem with this - it turned out that what I thought was the most perfect stack of stem and spacers vs the exposed steerer was actually about 1mm too short once torqued up and everything compressed down. Bike shop added a small spacer and all was sorted.