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stem expander cone 'nut'

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stem expander cone 'nut'

Old 01-01-22, 10:31 AM
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ehcoplex
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stem expander cone 'nut'

The first couple mm of threading of the cone-shaped expander nut of the stem on my '72 PX-10 are stripped. The cone is a very tight fit in the stem and the bolt is just long enough to reach it, but not long enough to get properly threaded.... So I either need a new expander cone, or a longer bolt (M8x1.0 x 155mm or more.....), and I'm not coming up with either. Other than finding a new/old stem (which maybe isn't a bad idea, I'm not sure if what I've got isn't a 'suicide' stem- it is an AVA..... though I do kind of want to keep the bike as original/period as I can), anyone know of a source or have any ideas?



Last edited by ehcoplex; 01-01-22 at 10:36 AM.
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Old 01-01-22, 11:07 AM
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Moe Zhoost
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If it has two slots, it's almost certainly a "suicide stem". Some of the single slot stems are suspect as well, needing routine inspection. I have a single slot AVA on one of my bikes and am fairly comfortable with it.

Re: your issue - Have you tried gently tapping the cone into the stem so that you gain a few millimeters? I don't think that would expand the stem too much so that it wouldn't fit the steerer tube. I'd also suggest filing the bottom of the stem to gain some space. I've done this with wedge-style stems when the wedge threads are partially stripped. You could also remove the bolt washer to install the stem. If this got the stem nice and tight, you could then remove the bolt and reinstall the washer.

Good luck.
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Old 01-01-22, 11:55 AM
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If you're not at the minimum insertion height and it's not a suicide stem you could cut off a few millimeters off the bottom of the stem and lengthen the slot(s) if necessary to give you a better thread purchase. However, I'm suspicious that your bolt isn't long enough to go through the cone nut. It sounds to me like something is amiss there so perhaps you'd be better off buying a different stem..
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Old 01-01-22, 01:35 PM
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ehcoplex
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Originally Posted by Moe Zhoost View Post
If it has two slots, it's almost certainly a "suicide stem". Some of the single slot stems are suspect as well, needing routine inspection. I have a single slot AVA on one of my bikes and am fairly comfortable with it.

Re: your issue - Have you tried gently tapping the cone into the stem so that you gain a few millimeters? I don't think that would expand the stem too much so that it wouldn't fit the steerer tube. I'd also suggest filing the bottom of the stem to gain some space. I've done this with wedge-style stems when the wedge threads are partially stripped. You could also remove the bolt washer to install the stem. If this got the stem nice and tight, you could then remove the bolt and reinstall the washer.

Good luck.
It's a single slot, and otherwise looks in good shape. Those are good tips & I think some combination ought to do the trick.
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Old 01-01-22, 02:10 PM
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Originally Posted by davester View Post
If you're not at the minimum insertion height and it's not a suicide stem you could cut off a few millimeters off the bottom of the stem and lengthen the slot(s) if necessary to give you a better thread purchase. However, I'm suspicious that your bolt isn't long enough to go through the cone nut. It sounds to me like something is amiss there so perhaps you'd be better off buying a different stem..
I think it's probably a combination of corrosion, pitting, etc. I probably will end up with a taller stem as the bike is just on the small size for me, but I'll try removing a couple mms first.
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Old 01-01-22, 03:51 PM
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If the cone is stripped or threads compromised then it is probably not safe to ride.

any thoughts from the group about converting the stem to a wedge ? has anybody done that ?

you'd need a donor stem or lower wedge piece

/markp
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Old 01-01-22, 04:18 PM
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Originally Posted by mpetry912 View Post
If the cone is stripped or threads compromised then it is probably not safe to ride.

any thoughts from the group about converting the stem to a wedge ? has anybody done that ?

you'd need a donor stem or lower wedge piece

/markp
The cone is 13mm or so tall, and it's only the top 3 or so mm of threading that is stripped, the rest is fine. But with the bolt being just long enough to engage and pull the cone up into the stem if the threads are good all the way to the top means I couldn't get enough threading to engage to get it started. But I cut about 4mm from the bottom of the quill and that was enough for the bolt to engage and then get several full turns of tightening.
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