Uneven clamping of stem on steerer tube
03-08-17, 11:27 AM
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Uneven clamping of stem on steerer tube
When I clamp my OEM Cannondale stem on my Synapse steerer, it seems that for an equal torque, the top and bottom bolt do not clamp equally (see attached picture - you can see more threads showing for the bottom bolt). Is this cause for concern?
The top cap and expansion plug were mounted according to the manual: expansion bolt torqued at 6Nm, expansion plug at bottom bolt location, preload properly set with top cap, and there is the required (by Cannondale) 2mm gap between the top of the steerer tube and the top cap. I torqued both bolts of the stem to an even 5Nm, alternating 1/4 of turn on each (properly greased) bolt.
I'm worried that what seems like uneven clamping might deform the top of the steerer or stress it the wrong way and eventually cause it to fail. The bottom bolt seems to be better supported by the expander in the steerer than the top one is by the upper part of the headset assembly. I can make both clamps look equal, but that would require me to torque the upper bolt less than the bottom one, which I think isn't really a better alternative as it would put uneven pressure on the steerer.
Is this normal? Do all Synapse stems look that way when properly clamped to a Synapse steerer? My LBS mechanic seems to think it's not something to be worried about, but I'd rather make sure than take a risk with my safety.
Oh by the way, don't mind the vertical line - it's not a crack, all Synapse steerer have it (some kind of join). It looks bad because of the flash.
The top cap and expansion plug were mounted according to the manual: expansion bolt torqued at 6Nm, expansion plug at bottom bolt location, preload properly set with top cap, and there is the required (by Cannondale) 2mm gap between the top of the steerer tube and the top cap. I torqued both bolts of the stem to an even 5Nm, alternating 1/4 of turn on each (properly greased) bolt.
I'm worried that what seems like uneven clamping might deform the top of the steerer or stress it the wrong way and eventually cause it to fail. The bottom bolt seems to be better supported by the expander in the steerer than the top one is by the upper part of the headset assembly. I can make both clamps look equal, but that would require me to torque the upper bolt less than the bottom one, which I think isn't really a better alternative as it would put uneven pressure on the steerer.
Is this normal? Do all Synapse stems look that way when properly clamped to a Synapse steerer? My LBS mechanic seems to think it's not something to be worried about, but I'd rather make sure than take a risk with my safety.
Oh by the way, don't mind the vertical line - it's not a crack, all Synapse steerer have it (some kind of join). It looks bad because of the flash.
03-08-17, 11:39 AM
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Many carbon fork steerer manufacturers want to have the steerer extend slightly above the stem and a spacer is placed on top of the stem to attain the top cap's ability to draw down properly.
Are you sure the stem's slot is even to begin with? A simple test with the stem upside down might lend more data. Or trying another stem to see how it closes up. Andy
Are you sure the stem's slot is even to begin with? A simple test with the stem upside down might lend more data. Or trying another stem to see how it closes up. Andy
03-08-17, 12:12 PM
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Many carbon fork steerer manufacturers want to have the steerer extend slightly above the stem and a spacer is placed on top of the stem to attain the top cap's ability to draw down properly.
Are you sure the stem's slot is even to begin with? A simple test with the stem upside down might lend more data. Or trying another stem to see how it closes up. Andy
Are you sure the stem's slot is even to begin with? A simple test with the stem upside down might lend more data. Or trying another stem to see how it closes up. Andy
No idea if the stem's slot is even. I'll probably need to try it.
03-08-17, 01:41 PM
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Rather than going by number of 1/4 turns you might consider going by torque value, perhaps alternately torqueing to 1, 3 and finally 5 N-m after taking up the slack.
In addition to Andrew's excellent suggestions regarding the slot width and flipping the stem you might check the diameter of the steerer for uniformity. Any difference in the diameter will be amplified by 6.28 (2*pi) on the circumference; check this with and without the expansion plug to see if there is any difference. Also check the ID of the stem for any burrs or debris which might interfere with uniform tightening.
In addition to Andrew's excellent suggestions regarding the slot width and flipping the stem you might check the diameter of the steerer for uniformity. Any difference in the diameter will be amplified by 6.28 (2*pi) on the circumference; check this with and without the expansion plug to see if there is any difference. Also check the ID of the stem for any burrs or debris which might interfere with uniform tightening.
03-08-17, 02:31 PM
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Rather than going by number of 1/4 turns you might consider going by torque value, perhaps alternately torqueing to 1, 3 and finally 5 N-m after taking up the slack.
In addition to Andrew's excellent suggestions regarding the slot width and flipping the stem you might check the diameter of the steerer for uniformity. Any difference in the diameter will be amplified by 6.28 (2*pi) on the circumference; check this with and without the expansion plug to see if there is any difference. Also check the ID of the stem for any burrs or debris which might interfere with uniform tightening.
In addition to Andrew's excellent suggestions regarding the slot width and flipping the stem you might check the diameter of the steerer for uniformity. Any difference in the diameter will be amplified by 6.28 (2*pi) on the circumference; check this with and without the expansion plug to see if there is any difference. Also check the ID of the stem for any burrs or debris which might interfere with uniform tightening.
And if there is a difference in circumference (probably caused by the expander), does that makes the uneven clamping a the same torque acceptable?
