Proper torque spec for stem top-cap screw?

Discuss light weight issues concerning road bikes & parts.
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VTBike
Posts: 412
Joined: Mon May 16, 2011 8:14 pm

by VTBike

Just wondering if anyone knows off-hand the proper torque spec for a typical stem top cap screw, with a carbon steerer tube/and typical expander plug? I usually just crank these things down - as I've never seen a spec.. but i'm sure there is one.

Thanks

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strobbekoen
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Location: BELGIUM

by strobbekoen

You just tighten it to take the play out of the headset.
That's it sole purpose.
No need to crank it down hard, and if you have to, there is a problem.

by Weenie


thisisatest
Shop Owner
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by thisisatest

holy crap-6Nm? if that's for the expander wedge part of a compression plug assembly, it seems fine. for the actual top cap bolt, the one that does the preloading, dia-compe's Aheadset original instructions were for 5-15 in/lb, aka very little. i think Chris King was 25-35 in/lb, but that's just off the top of my head... the idea is to have the headset as loose as possible while having no play.

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Cyco
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Joined: Sat Nov 30, 2002 4:49 am

by Cyco

As little as possible.

6Nm would lead to binding on most headsets. I only ever adjust to take play out, I'd be guessing 2-4, but its all bike dependant. Not a place for a torque wrench
Success is how far you you bounce back up after being knocked down

em3
Posts: 887
Joined: Tue Dec 23, 2008 2:57 pm
Location: NYC

by em3

VTBike wrote:I usually just crank these things down



Yikes!!! Sounds like a tutorial is required reading for you.

http://www.parktool.com/blog/repair-hel ... et-service

As others have said, you only need to tighten enough to remove play from bearings...any additional torque is simply overkill and will damage your bearings. The purpose of the topcap is only to provide the proper compression for your headset bearings. After you reach proper bearing adjustment and torque down your stem to steertube, it really serves no other function....you can essentially ride without a topcap.

EM3
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thechad
Posts: 35
Joined: Sat Mar 19, 2011 10:13 pm

by thechad

FYI, I just played around with 2 headset top caps here...one on a Wilier carbon and one on a P4. There is some art to getting them tight enough to take the play out but not so tight as to limit bearing movement...3 nM seems to be about right on both of these bikes for me.

kresyzig
Posts: 222
Joined: Sat Apr 16, 2011 8:49 pm
Location: Ottawa, ON, Canada

by kresyzig

Yeah the proper torque for the top cap is probably too low to be measured accurately with most torque wrenches.... I usually torque mine by squeezing the hex bits with my bare hands, check that there is no play by moving the bike back and forth with the front wheel locked using the brake, then I take the bike for a ride and test for play again...

VTBike
Posts: 412
Joined: Mon May 16, 2011 8:14 pm

by VTBike

Sweet, thanks for the replies. When I say "crank down on it" take it with a grain of salt.. These are carbon parts, so I'm pretty careful.. not like when torquing a crank or old style BB. I actually was surprised when I got my new smaller torque wrench that goes down to 3nm.. The specs on alot of my parts, like the carbon stem and seatpost clamp indicate a max torque of 5nm - which was way more than I would have done if I was just hand tightening. I still only torqued my stem front cap and stem bolts to 4nm.. 5 just seems like way to much. Never had anything close to an issue with the lower than max torque. My guess is that I have my top cap around 3-5 nm right now.. I will back it off a little to the point where it just takes the play out.

maquisard
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Joined: Thu May 01, 2008 8:51 pm
Location: France

by maquisard

As others have said, the top cap is pre-load only. You want the minimum torque to reduce play in the headset. Once the stem is tightened in place is is purely cosmetic and covers the top of the steerer. It is non-load bearing!

Same is true for the end-cap on a Shimano Hollowtech II crankset. It really annoys me when I see people holding the tool in vice grips and trying to use some crazy torque to tighten it. Shimano made the tool in that way for that particular reason!

by Weenie


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