Rookie mistake, stripped seatpost clamp thread

[jeff_o]

Hi. I just discovered that i have stripped my seat post clamp thread already. how would 9NM feel? any tips for those who do not have torque wrenches?

Also, when I buy a replacement clamp in ebay. how do I measure the size? is it the inner diameter of the clamp (i measured roughly 31.+mm)? or it is just the seatpost size (27.2mm)?

cheers all!

[Dan]

That's a relative thing, feeling. It would feel different, dependent upon a number of factors, for example the length of your wrench.

For me, using a 150mm 1/4" drive, it feels like tightening with wrist strength, then a final nudge with some push through the shoulder as well, if that makes sense to you. However, you don't know what my wrist strength is like, nor that of my shoulders, and that's sort of the point.

You can get a small torque wrench for about $45 - well worth it. Since you have to order a new seatpost clamp, the shipping on the wrench is effectively free

[ozdavo]

You can measure torque with basic tools and a luggage scale or similiar:
http://www.bicycles.net.au/forums/viewtopic.php?t=52730&p=801283#p800804
See post 188


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[TDC]

Heaps of clamps on sale at tropedo7 at the moment...on sale too. If you are planning on doing your own basic maintenance regularly, a torque wrench is handy in your toolbox.


http://www.torpedo7.com.au/products/T7T ... wrench-set

[il padrone]

Have been fixing, maintaining and building bikes for 35 years and I've never used a torque wrench. Personal torque wrenches have only become a common item with the growth of carbon frames and components. Really for a steel or alloy frame and components it should not be necessary.

You obviously used too much grunt. Learn from this. For your seat post clamp you need to tighten it sufficient that your seat post does not rotate if you push it and does not slide down when you are riding - no more. Trial and error, but better to err on the 'too little' than 'too much' to preserve your components. You can always tighten it some more if it is slipping (you do of course carry some basic tools when riding?)

[munga]

exactly. i would use as much effort as it takes to keep the ants out of my peanut butter jar. or 9Nm.
ug man tighten till metal groan. then tighten bit more.

[jeff_o]

thanks mates. i used to tighten them lightly by hand but then noticed my seatpost slipping after each ride so i tightened some more but unknowingly stripping the threads.

[find_bruce]

Also, when I buy a replacement clamp in ebay. how do I measure the size? is it the inner diameter of the clamp (i measured roughly 31.+mm)? or it is just the seatpost size (27.2mm)?

Is anyone able to answer this question ?

[ozdavo]

Also, when I buy a replacement clamp in ebay. how do I measure the size? is it the inner diameter of the clamp (i measured roughly 31.+mm)? or it is just the seatpost size (27.2mm)?

Is anyone able to answer this question ?

You need a 31.8mm clamp

[rkelsen]

Meh. Drill it out and use a slightly longer stainless steel bolt & nut.

[eeksll]

Also, when I buy a replacement clamp in ebay. how do I measure the size? is it the inner diameter of the clamp (i measured roughly 31.+mm)? or it is just the seatpost size (27.2mm)?

Is anyone able to answer this question ?

internal diameter of clamp or i assume more correctly the outer diameter of the part the clamp goes on, so that would be the outer diameter of the top of the seat tube.

[Nobody]

Hi. I just discovered that i have stripped my seat post clamp thread already. how would 9NM feel? any tips for those who do not have torque wrenches?

As said, you can use scales on the end of your tool and work out what 9Nm should be in Kg on the scale at the length from the pivot point. You can also hang specified weight from the tool to do the same. In the end, keep in mind that although torque wrenches are more accurate than just estimating, even an accurate torque wrench is only 25% accurate for the resultant bolt stretch, which is what you are trying to achieve. Too little bolt stretch and the bolt will work loose. Too much and it will break, or in your case, strip. Torque also varies with the inaccuracy of the torque wrench and the thread lubricant used. Torque wrenches have to be calibrated at point of sale to be really accurate and then recalibrated regularly.

Like IP above, I don't use a torque wrench on bikes as I've developed a feel for small bolt stretch over many years. I do for bigger bolts used on cars though.

Also, when I buy a replacement clamp in ebay. how do I measure the size? is it the inner diameter of the clamp (i measured roughly 31.+mm)? or it is just the seatpost size (27.2mm)?

Measure the outside of the frame with vernier calipers. If you don't have one, I would suggest it is a worthwhile purchase if you going to be mucking around with bike parts in the future. I use mine regularly. Another option would be to measure the circumference using tape or string then work out the diameter from that. Then get the closest commonly available clamp. Since you have a tendency to overtighten, I suggest you get a clamp with an oversized bolt and/or a supporting steel nut/insert for the clamp.

I have both clamps below. They can take some torque without stripping or snapping. Cleaning and relubricating the bolt with grease from time to time should reduce the chance of stripping in the future.

http://www.chainreactioncycles.com/Mode ... elID=19216


http://salsacycles.com/components/lip_lock
http://www.aebike.com/Salsa-Lip-Lock-32 ... 27882.html

Another option is a dual diameter clamp. As the top clamp is direct on the seatpost, in theory, it doesn't need as much pressure to grip. Also just the fact you have two bolts means each bolt is needs less clamping pressure. I have one of these on my MTB and it holds fine without excessive bolt stress.

http://www.carboncycles.cc/?s=0&t=2&c=73&p=851&

One reason you may be over-tightening is due to seatpost slip. If this is the case, then I suggest removing any grease and then replacing it with a carbon component assembly paste, or non-hardening gasket sealant like Loctite No 3.