LBS and Torque Wrench

Hi all,

On Saturday, I had a need to use a bike shop outside of my area while visiting family. The shop has a fantastic reputation in the area. While I was there, I asked him to chuck some carbon grease on my seat post and I was surprised to see him NOT use a torque wrench when tightening it back up, on a carbon frame.

Would you expect this? I am not mechanically minded but I have always been told that you should ALWAYS use the correct torque on any carbon frame fixings but maybe I am naive and falling for industry hype. I guess he was confident of his own judgement but why would a bike shop take any risks.

I welcome your thoughts

Mike
 

DCBassman

No, not the fish...
Location
Ten Forward
A good mechanic can judge these things more accurately than you might imagine, but I'm still surprised on a carbon frame.
 
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mikeloveshisrockhopper

mikeloveshisrockhopper

Active Member
The mechanic is a plonker, nobody can judge accurately what 4Nm is. Just plain lazy in my humble opinion.
That was my feeling. Even if he is super confident, just buy a torque wrench and use it, especially if the customer is standing there. Even I've got a torque wrench. I may even use it one day...
 
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mikeloveshisrockhopper

mikeloveshisrockhopper

Active Member
I would take it home and use a torque wrench to undo the screw. It would tell you how good the mechanic was.
I was tempted to do this, i.e. loosen it with a non torque hex key. If it comes loose very easily, would you say it was not tightened enough? I'll use my torque wrench then to tighten it back up.
 
Rather than loosen it, tighten it. Set the torque wrench to well below what it should be - the wrench should click as you try to tighten. Increment it a very small amount and try again. If you get to whatever it's supposed to be and it's still clicking then he's overtightened it (or got it exactly right, but those torque values are supposed to be upper limits, not targets, I believe?).
 

Ajax Bay

Veteran
Location
East Devon
I would take it home and use a torque wrench to undo the screw. It would tell you how good the mechanic was.
Not sure that this (implicit) test is valid. Is the torque required to undo a screw the same as the torque it's been tightened to? Will it matter if the screw's been in place for a while?
Edit: Cross post with @Sea of vapours , along the same lines. That test would be valid.
Can we assume that the seatpost is carbon?
 
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mikeloveshisrockhopper

mikeloveshisrockhopper

Active Member
Yes, carbon seat post. Anyway, I have just loosened it with a non torque allen key and I barely needed to put any pressure on it and it came loose! I reckon I could have moved it with my fingers if I could have got them into the recess. Surely this isn't right and he didn't tighten it enough? I knew I'd use my torque wrench one day.
 
. Surely this isn't right and he didn't tighten it enough?
Unfortunately you can't assume that. Firstly, the torque to undo something (a properly greased something anyway) is almost certainly less and, more pertinently, drops off very rapidly indeed once movement starts (try that, undoing with a torque wrench). Secondly, these 3-5Nm values are really tiny and 'done up properly' is an awful lot less than might seem reasonable; at least it seems that way to me. If there's carbon paste in there then a really small amount of torque is going to hold the post in place so it may well be that he'd done it 'just enough', which is better than 'just too much'.
 
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