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Discussion Starter · #1 ·
I flipped my stem last night and reinstalled my cateye computer on the stem/headset. The headset/top cap seem to be tight but the computer won't stay in one place, it spins fairly easily. What could I have done wrong?
 

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Diesel Engine
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It sounds like you left a spacer out, but you also have your headset adjusted wrong. The top cap should set the bearing preload, the stem bolts are just to clamp the stem to the steerer to hold it in place.

The easiest way to achieve this is to adjust the headset with the stem not tightened down to the steerer. Once the bearings are set properly using the top cap, align the stem straght ahead and tighten the steerer clamp bolts to spec.

Oh, and find that spacer! Do you have any steerer tube coming out of the top of the stem? If so the top cap is bottoming out on the fork, not the steerer (and the mount is likely spinning around the steerer, not getting compressed against the top of the stem). The steerer needs to be below the top of the stem (this includes any spacers on top of the stem which your computer mount effectively is) by a couple mm for the system to work properly.
 

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Mike Prince said:
It sounds like you left a spacer out, but you also have your headset adjusted wrong. The top cap should set the bearing preload, the stem bolts are just to clamp the stem to the steerer to hold it in place.

The easiest way to achieve this is to adjust the headset with the stem not tightened down to the steerer. Once the bearings are set properly using the top cap, align the stem straght ahead and tighten the steerer clamp bolts to spec.

Oh, and find that spacer! Do you have any steerer tube coming out of the top of the stem? If so the top cap is bottoming out on the fork, not the steerer (and the mount is likely spinning around the steerer, not getting compressed against the top of the stem). The steerer needs to be below the top of the stem (this includes any spacers on top of the stem which your computer mount effectively is) by a couple mm for the system to work properly.
You are making assumptions, what makes you think he didn't install his stem this way???

You mention your top cap is tight but are all the spacers under the stem tight? As Mike states, you want to preload the headset before tightening the stem.

Don't use my o-ring trick unless yo uare sure you installed everything correctly. The o-ring sohudl only serve to give a little extra resistance should your unit turn when you hit bumps. From your description this isn't the case right now.
 

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Discussion Starter · #10 ·
PissedOffCil said:
You are making assumptions, what makes you think he didn't install his stem this way???

You mention your top cap is tight but are all the spacers under the stem tight? As Mike states, you want to preload the headset before tightening the stem.

Don't use my o-ring trick unless yo uare sure you installed everything correctly. The o-ring sohudl only serve to give a little extra resistance should your unit turn when you hit bumps. From your description this isn't the case right now.
I'm slightly confused now. When I removed the stem and headset, I remember using a smaller allen wrench to loosen something deep down inside the headset, but then a larger diameter allen wrench to loosen the actual cap. When I reinstalled the headset, it seemed like the bolt deep inside the headset was either stripped or just kept spinning - it never got tight. I then used the bigger wrench to tighten the cap.

I don't remember at what point I tightened the bolts securing the stem.

Did I do something wrong?
 

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Diesel Engine
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PissedOffCil said:
You are making assumptions, what makes you think he didn't install his stem this way???
Perhaps, but they are logical assumptions in an attempt to help him. And I followed up the assumption with some logic. Which is more than what you have given him. Thanks.
 

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Diesel Engine
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MoreBoostPlease said:
I'm slightly confused now. When I removed the stem and headset, I remember using a smaller allen wrench to loosen something deep down inside the headset, but then a larger diameter allen wrench to loosen the actual cap. When I reinstalled the headset, it seemed like the bolt deep inside the headset was either stripped or just kept spinning - it never got tight. I then used the bigger wrench to tighten the cap.

I don't remember at what point I tightened the bolts securing the stem.

Did I do something wrong?
Can you take the top cap out and take a picture of what you are talking about? It sounds like you have an expander plug instead of a cap.

From your description, yes you may have done something incorrectly. Not catastrophic by any means, but it doesn't sound like things went back together the way they came apart. It also sounds like you did more than just loosen the stem and flipped it from this post.

Edit - when you turn the handlebar does the front end turn without resistance? If you lock the front brake and pull back and forth ont the bars is there play (clunking) in the front end? I wouldn't ride the bike till you know the headset is adjusted correctly, best case could be that you ruin the bearings if you ride it.
 

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Discussion Starter · #13 ·
Mike Prince said:
Can you take the top cap out and take a picture of what you are talking about? It sounds like you have an expander plug instead of a cap.

From your description, yes you may have done something incorrectly. Not catastrophic, but it doesn't sound like things went back together the way they came out. It also sounds like you did more than just loosen the stem and flipped it from this post.
I'll try to get a picture.

It's funny - I can replace just about anything on a car, but I'm still clueless when it comes to a bicycle. :mad2:
 

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Mike Prince said:
It sounds like you have an expander plug instead of a cap
Sure does.

The expanding element sits inside the steerer tube. Turning the expander screw (accessed through the top cap hole) clockwise with the smaller Allen expands it against the inside wall of the steerer tube. When tight enough, it becomes the anchor for the cap to pull itself against and compress the headset / pre-load the bearings.

Because you turned the expander screw counterclockwise with your smaller Allen, you loosened the expanding element. You tried to re-tighten it, but may not have tightened it quite enough. So instead of serving as an immovable anchor, it's possible the expanding element may have pulled itself up to the cap when you turned the cap clockwise with your larger Allen.

Not all expander plugs look or function exactly like this, but this is basically how they work.
 

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Discussion Starter · #15 ·
wim said:
Sure does.

The expanding element sits inside the steerer tube. Turning the expander screw (accessed through the top cap hole) clockwise with the smaller Allen expands it against the inside wall of the steerer tube. When tight enough, it becomes the anchor for the cap to pull itself against and compress the headset / pre-load the bearings.

Because you turned the expander screw counterclockwise with your smaller Allen, you loosened the expanding element. You tried to re-tighten it, but may not have tightened it quite enough. So instead of serving as an immovable anchor, it's possible the expanding element may have pulled itself up to the cap when you turned the cap clockwise with your larger Allen.

Not all expander plugs look or function exactly like this, but this is basically how they work.
This is exactly what the issue was - an expander plug. It only took a few minutes for me to reassemble everything correctly and now, not only does the computer sit tight, the front fork is secure.

Thanks for the help!! Everyday I learn something new about bikes.
 

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Yeah you definitely omitted some details in your original post. Glad you got it back working.

Some details that might be of interest. The expander plug serves as an alternative to the old starnut. With the advent of cable steerers, they had to find an alternatiove as people didn't feel confident scratching the inside carbon of the steer tube. So they started using expander plugs that you thread your top cap in to preload the headset.

They can be a pain to setup without the right tricks. It usually requires putting it in the steer tube tight but often they spin in place when trying to tighten them more. The trick is to tighten your stem over the steerer then tighten the plug, loosen the stem, retighten the plug, etc until you get the proper tightness for the plug.

As far as depth is concerned, I thread the topcap bolt into the expander plug until it starts to come out underneath then push it in the steerer and follow the above procedure.
 

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Discussion Starter · #17 ·
PissedOffCil said:
Yeah you definitely omitted some details in your original post. Glad you got it back working.

Some details that might be of interest. The expander plug serves as an alternative to the old starnut. With the advent of cable steerers, they had to find an alternatiove as people didn't feel confident scratching the inside carbon of the steer tube. So they started using expander plugs that you thread your top cap in to preload the headset.

They can be a pain to setup without the right tricks. It usually requires putting it in the steer tube tight but often they spin in place when trying to tighten them more. The trick is to tighten your stem over the steerer then tighten the plug, loosen the stem, retighten the plug, etc until you get the proper tightness for the plug.

As far as depth is concerned, I thread the topcap bolt into the expander plug until it starts to come out underneath then push it in the steerer and follow the above procedure.
I didn't even realize the fork was loose (until I took it down) - the bike was hanging on a wall mounted bike rack.

The procedure I followed sounds just like what you described. Hopefully I got the depth set correctly though.
 
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