I have an issue with my Cannondale Topstone gravel bike (yeah, yeah, I know there will be those who think the biggest issue is that it's a gravel bike 🙂 )
The headset / stem seems to work loose. It's a carbon steerer with a cannondale steerer bung thing and cannondale alloy stem. It works loose, ever so slightly and needs nipping up every 150kms or so (loosen stem, nip up the bearing play, tighten stem; it seems to happen more often over rough ground, or perhaps the ground just means I notice it sooner). It's a PITA.
I know in theory the bung does nothing once the stem is tight, but is it possible it's slipping slightly thereby allowing the stem to slip too? Carbon paste on the inside of the steerer round the bung?
What is the thought here on carbon paste on the stem/steerer part of carbon steerer forks? The collective wisdom on the internet seems to have differing views on the topic.
Anything else I can check ? Someone suggested to me that I try a different stem. If anyone has seen and solved something similar or has bright ideas to share, I'm very keen...
Remove topcap, check if the bung is secure, hex key beyond screw thread for topcap.
I've had this before, due to what I can only assume was a slightly flexible steerer allowing the stem to 'walk' up the stem.
Sand the inside of the SRAM or the steerer with coarse sand paper and it will hold better.
Stem stupid autocorrect
I know in theory the bung does nothing once the stem is tight
I don't think that's quite true for a carbon steerer. I think it pushes the steerer tube out, opposing the stem, so that the steerer is effectively clamped between the stem and the expander.
This happens a lot on mine. The manufacturer said to put some carbon assembly paste inside the stem.
I think it's a combination of carbon steerer and the absolute pounding a rigid gravel bike headtube gets if ridden on proper rough stuff.
As Aidy says, bungs for carbon steerers are meant to reinforce the steerer where it clamps, to resist clamping forces.
Unless it's a tight fit it may not be doing this job so well.
Solved this on a CAAD12 with carbon steerer and SI top cap/bung by using an FSA microshim under the top cap.
The depth of the insert for the top headset bearing is marginally over. The reducer inside the top bearing does a good job of hiding the play under inspection on a workstand, but get out riding and you'll feel the play again.
The dealer kept shoving loads of grease in there, few miles later it would be back. They even changed the top cap and reducer for FSA instead of Cannondale.
I decided to swap out the bearings to rule them out, after doing it and clearing out swathes of grease the dealer had left I could feel that it was impossible for the top cap to compress the reducer. Chucked a spare micro-shim in and problem sorted.
When you say shim under the top cap I assume you're referring to the conical spacer/bearing cover rather than the cap at the top for preload?
I've had the same (and the same trouble spotting it!). Shim under the cap sorted it.
Thanks all - I did think the "absolute pounding" and carbon steerer together may help. I'm going to take it all apart today and inspect it properly for anything that seems out of kilter... Let's see...
Yes sorry I mean conical spacer that sits on top of the top bearing. Stick directly under that above the reducer.
I think I've figured it out. the top of the stem isn't parallel to the end of the steerer and at the front there isn't enough gap from the top of the steerer to the top of the stem for the cap to fit in. It doesn't fit flush... Calling the bike shop tomorrow - assume that a bit will need lopping off the steerer...
I believe it is common to use a single thin spacer above the stem so the cap can be tightened without contacting the top of the steerer...the reasoning being that the stem needs as much carbon as possible to contact... cutting down the steerer means the top stem bolt can crush the top of the steerer rather than grip firmly
Cannondale state all over their tech docs to never shim above the stem, and with the Cannondale expanding plug there is little adjustment of the top cap with the bung in the correct place (i.e. at the bottom of the stem to support the clamping). It may be lawyers deciding rather than the engineers, but I'm going to have the shop decide how they want to fix it to avoid any warranty discussions down the line...
EDIT : and the same cannonale tech docs state steerer to be 3mm below the top of the stem. It's less than 1mm at teh front and not 3 at the back. Stem doesn't look straight, to be honest, I may think about swapping it...
Not likely that stem is not square is it? Who cut the steerer?
No-one so far as I am aware, it's like that from new. Eyeballing it, the steerer end looks squarer than the stem, that's all I can say.
orangespyderman
......Cannondale state all over their tech docs to never shim above the stem, and with the Cannondale expanding plug there is little adjustment of the top cap with the bung in the correct place (i.e. at the bottom of the stem to support the clamping). It may be lawyers deciding rather than the engineers........
yep bit out of date mrs antigee has a specialized ruby and that has no spacer
guess my concern would be that essentially Cannondale are using a system that needs tolerances to be met and they aren't...so either the steerer is outside specified length / not cut straight or the headset bearings aren't set correctly whatever it is a quality issue...no way is a stem slackening off normal even if being abused big time
Cannondale state all over their tech docs to never shim above the stem,
How odd - I can't think of any reason to not have spacers above the stem.
And particularly for a gravel bike, you might want to move the bars up/down a little depending on if you're doing more road/gravel.
How odd – I can’t think of any reason to not have spacers above the stem.
I'm guessing, they want the fork bung to be on the inside of the stem to push back the force of the stem clamping.
If you put spacers above the stem, the fork bung will be on the inside of the spacers and not on the inside of the stem and could fail.
They don't want to spec a long fork bung as they are heavier?
I’m guessing, they want the fork bung to be on the inside of the stem to push back the force of the stem clamping.
Right. Of course - that's the point I made earlier.
I'd been thinking one or two spacers, which shouldn't affect it too much, but I guess some people might go mad with it.
If this works it's a picture of the setup I had, hopefully explains a few hundred words.
Spacers on top mean the top cap doesn't support the top part of the steerer tube as designed/stipulated by lawyers.
Bung in wrong place means the lower part of the steerer above headtube isn't supported as blah blah.