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Our oldest son has been alternating between mine and my wife’s bike (Carreras from Halfords) whenever he has to go anywhere, but over the last week or so we noticed he had stopped using my bike, saying the other one was more comfortable. I was moving the bikes into the shed last night and noticed that the stem cap and bolt (think that's they're called) are missing!! Don't know what he did and I've not had a chance to talk to him about it yet. Here is a picture of the bit I'm talking about:

enter image description here

Is this an easy part to source and is it difficult to fit correctly? Am I better just taking the bike into Halfords and asking them to fix it (assuming they can)?

Update, I've got what I thought I needed and went to fit it today. But it seems there's something else missing! I've taken pictures, can anyone see what the issue might be: enter image description here

Thanks Swifty, didn't notice I'd posted the wrong picture. Here is a better one, it looks like there should be something inside the star. The bold is just spinning.

enter image description here

Thanks

Alex

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  • Those should be available at any bikeshop.
    – Carel
    May 22, 2019 at 7:38
  • Might be a good chance to talk with him about being forthcoming, and what to do when you borrow someone's stuff. IE, return in the condition it was lent.
    – Criggie ♦
    May 22, 2019 at 8:17
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    @Criggie - yep, that's a conversation that'll be happening. You'd think a 24 year old would know better!!
    – Alex Goldie
    May 22, 2019 at 8:44
  • My suspicion is he was attempting adjust the bars to a more comfortable position. On older quill stems the bolt you would loosen to raise or lower the stem is in the same position as your missing piece. Perhaps a new adjustable stem could make the bike comfortable for all concerned.
    – mikes
    May 22, 2019 at 13:35
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    @Swifty - I've added a better picture, the issue the bolt is just spinning when I try to fit it.
    – Alex Goldie
    May 28, 2019 at 7:40

3 Answers 3

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The cap and bolts are readily available, if you want no need to stick to a boring round black thing - they come in all sorts of weird and wonderful shapes, colours and functions. You can get them with bottle openers and clocks.

The cap and bolt is only needed to set the preload on the bearings when installing the stem. Once the stem bolts are done up, the cap and bolt does nothing (although for safety, I would not ride a bike with no cap). Therefore if you do not undo the stem bolts, all you need to do is put on the new cap and do the bolt up. The bolt only needs to be tight enough it does not come undone - 5nm should be enough (that is not much). You do not want to be a gorilla on the end of the spanner.

If you have undone the stem bolts, you need to loosen the stem, do up the cap bolt till the play is removed from the head set, line up the handle bars and tighten the stem bolts (typically 5-7nm, much less than most people think).

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  • Thoughts on Grease?
    – Swifty
    May 22, 2019 at 8:57
  • I do grease (better - Anti-Seize if you have it around) as it protects against rust. There is a 'debate' of 'grease/don't grease bolts that comes from the changes to clamping forces when torqued accurately - but it does not apply to setting bearing preloads.
    – mattnz
    May 22, 2019 at 9:08
  • I bought one with an integrated 3 prong mount for a gopro case - its great.
    – Criggie ♦
    May 22, 2019 at 19:25
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Stem caps are easy to get and easy to install. The purpose of them is to take the play out of the headset. To do this you have to first loosen the two bolt of your stem and then tighten the cap bolt until there is no more play. Now you can tighten the bolts back on your stem.

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  • Thanks Airace3, I'll give it a try tonight.
    – Alex Goldie
    May 22, 2019 at 7:43
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    Once the stem bolts are tightened, the stem cap is no longer necessary (except that now water and dirt can enter the fork steerer). This also means that you can just screw in the new cap and bolt without having to undo and redo the stem bolts.
    – StefanS
    May 22, 2019 at 7:45
  • @StefanS I wouldn't be so sure, i had the headset on one of my bikes loosen over time with installed stem cap.
    – airace3
    May 22, 2019 at 8:02
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    @StefanS I would not ride a bike without a stem cap in place.
    – Criggie ♦
    May 22, 2019 at 8:17
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    I agree that it would feel strange to ride without stem cap, but from a mechanical point of view it's the pinch bolts that hold everything together.
    – StefanS
    May 22, 2019 at 8:40
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If the bolt you now have is just spinning freely, it sounds like there is no thread for it to engage. You could compare this one against the thread in your wife’s bike to double check.

The star shape item is a ‘star-fangled nut’ and is driven down into the steerer, the tangs resist the pulling up of the bolt. If it’s damaged you need to replace it. Sometimes people will drill the whole thing so it disintegrates, then fit a new one, or drive it all the way down and out the bottom.

Installing the new one requires a star nut setting tool which you aren’t going to use very often (hopefully!) so decide early if you’re going to do it yourself or accept paying labour on a shop doing it.

You can find tutorials for replacing a star-fangled nut online, if you have any problems it would now be best as another question, though you are very welcome to do so. You can always link back to this one for context.

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