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 Post subject: Giant Air Cap
PostPosted: Wed Aug 23, 2017 1:45 pm 
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Joined: Wed Aug 23, 2017 8:19 am
Posts: 5
Hi everybody,
this is my first message but I've been reading the forum for a long time...
I have a Giant Propel SL which came with the stock expander plug for the steering tube. Unfortunately the inner screw (the one that "expands") keeps coming loose even with blue Loctite and tightened at the right torque.
So I found on line the GIANT glued-in air cap, which seems to solve the problem and save some weight but it also looks completely irreversible. Is there a way to get that thing out in case you want to recut your steering tube (in case I sell the bike)?
Is it any better/worse than the original expander?
Thanks a lot!
r


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 Post subject: Giant Air Cap
Posted: Wed Aug 23, 2017 1:45 pm 


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 Post subject: Re: Giant Air Cap
PostPosted: Wed Aug 23, 2017 2:16 pm 
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Joined: Fri Dec 24, 2010 9:37 pm
Posts: 1354
Location: it's raining, it must be uk
the bung is mainly there to allow the top cap to be tightened and preload the headset before clamping the stem

after that it doesn't matter much, though there's a school of thought that the bung also supports the steerer tube against crushing force from the stem, but the screw loosening won't affect that

if the thing being loose bugs you, get another one, there're plenty of options, i'd avoid the glued-in one as once glued it's probably not going to shift

for instance https://www.universalcycles.com/shoppin ... egory=1695


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 Post subject: Re: Giant Air Cap
PostPosted: Wed Aug 23, 2017 2:29 pm 
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Joined: Wed Aug 23, 2017 8:19 am
Posts: 5
thanks for your reply but unfortunately when it come loose it develops the typical "loose headset" play that I hate so much (you can feel it by pulling the front brake and moving the bike back and forth)...I forgot to mention that the steering tube is 1.5"..


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 Post subject: Re: Giant Air Cap
PostPosted: Wed Aug 23, 2017 5:26 pm 
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Joined: Thu Jun 03, 2010 12:47 pm
Posts: 152
Yes you can take the glued on off again. My LBS is a Giant dealer and they use to take those out. It comes with a tube of regular superglue (gel) so if you put a lot of spacer above the stem, put a headset top cap and tighten the bolt it will eventually unstick the glued nut. Same "theory" as used to take bearings out


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 Post subject: Re: Giant Air Cap
PostPosted: Thu Aug 24, 2017 1:22 am 
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Joined: Tue Sep 09, 2014 9:30 am
Posts: 805
Robsurf wrote:
thanks for your reply but unfortunately when it come loose it develops the typical "loose headset" play that I hate so much (you can feel it by pulling the front brake and moving the bike back and forth)...I forgot to mention that the steering tube is 1.5"..

This shouldn't happen if your headset is preloaded and your stem is tightened correctly.


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 Post subject: Re: Giant Air Cap
PostPosted: Thu Aug 24, 2017 7:21 am 
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Joined: Sun Aug 06, 2017 8:27 am
Posts: 6
Robsurf wrote:
thanks for your reply but unfortunately when it come loose it develops the typical "loose headset" play that I hate so much (you can feel it by pulling the front brake and moving the bike back and forth)...I forgot to mention that the steering tube is 1.5"..


If your headset is becoming loose that means that your stem is slipping on the steering tube. That would explain why the top cap is becoming loose, since the slight movement of the stem and spacers up and down the steering tube could be slowly pushing it up, and loosening it.

If I'm not mistaken your bike should have a carbon steerer and a carbon stem. I'd recommend taking the stem off, cleaning both stem and steering tube at the interface points (where they touch each other), applying carbon mounting paste to the area and putting the stem back. Of course, you should tighten it using a torque wrench.
Apply the mounting paste after you've dropped in the lower spacers, otherwise the spacers could push some of the mounting paste (which is abrasive by nature) down into the headset bearings, and you definitely don't want that.

With a correctly preloaded headset bearing and correctly torqued stem you could even get rid of the top cap and it wouldn't develop any wiggle or looseness. Some people actually do that to shed a few grams, but I don't recommend it.

Remember that the top cap has 2 functions:

1. It allows you to preset the headset bearing tension.
2. It prevents (more or less) water from entering your steerer and headset bearings.

Some people claim that the stem already seals that area from the top well enough, but when you're riding and pulling on the handlebars even the stiffest stem will deform and "rock" up and down / side to side very slightly, but that's enough for water and sweat to flow through that minuscule gap and ruin or corrode your headset bearings sooner than expected.
Water and sweat won't mix with the grease that's down there, but the repetitive movements will end up creating a dirty emulsion of grease + sweat + water that is not exactly healthy for those materials.

/end of rant.


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 Post subject: Re: Giant Air Cap
PostPosted: Thu Aug 24, 2017 1:19 pm 
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Joined: Wed Aug 23, 2017 8:19 am
Posts: 5
thanks to all for your comments, I really appreciate!
I am not completely new to bike mechanic (I bought the frame only and mounted myself, including cutting of the carbon steering tube and seat mast as well as mounted several mountain bikes in the past few years) but despite having used carbon paste and torque wrench the thing keeps coming loose. I think I'll give the glue-in cap a try...


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 Post subject: Re: Giant Air Cap
PostPosted: Thu Aug 24, 2017 2:52 pm 
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Joined: Thu Jun 03, 2010 12:47 pm
Posts: 152
You probably have a problem somewhere elsewhere. I never had a loose headset on my TCR adv SL both with removable expanser and the glued one!


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 Post subject: Re: Giant Air Cap
PostPosted: Thu Aug 24, 2017 4:21 pm 
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Joined: Wed Aug 23, 2017 8:19 am
Posts: 5
well for me it is actually pretty straight forward.. I tighten the expanded, the top cap, the stem all of the above at the right torque. I rock the bike back and forth with the front brake pulled: no play. After 2-3 weeks I do the same rocking test and I feel a play. So I undo the stem, the top cap and find the expander just a little too loose...it can be a faulty expander but it can't come from anything else....


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 Post subject: Re: Giant Air Cap
PostPosted: Thu Aug 24, 2017 5:08 pm 
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Joined: Fri Dec 24, 2010 9:37 pm
Posts: 1354
Location: it's raining, it must be uk
no, it's the stem slipping - barring unusual effects like the headset slowing settling into the frame, something collapsing/stretching etc...

if you clamped the stem with the headset loaded, and the headset has become unloaded, it's proof the stem has moved

even without the top cap, the stem should not slip, once the preload is set and the stem clamped, it should be possible to ride safely without the top cap being there

as it is, presumably the slipping stem is applying force to the underside of the top cap and driving the bung up - normally the bung has only to resist the force of setting the preload, not the extra force due to the slipping stem

the problem is not the top cap/bung, the problem is that the stem is slipping

you need to stop the stem slipping


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 Post subject: Re: Giant Air Cap
Posted: Thu Aug 24, 2017 5:08 pm 


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