i pinched seat tube putting on problem solvers brand front derailleur clamp

[JP]

On unhealthy air days i've been playing around - trying out different parts to see what happens and learn about maintenance.  

I have a torque wrench but not a lot of experience with it.  When putting on a braze on clamp adapter i made a little pinch in and seat tube and that makes me a bit sad.    The clamp said to use 4 NM and that's what i sent the wrench at.

It's a steel sam h. that will likely be fine - but any tips  to avoid this type of damage going forward?

(like i was thinking should i tighten slower or lubricate the clamp or something?). 

thanks in advance!

JP

[Joe Bernard]

I kind of hate front derailleur clamps for just this reason, it's stupid-easy to over-tighten them and gouge the paint. First, it's probably just paint..I will be very surprised if you cranked on it hard enough to damage the tube. It's still a bummer on your nice frame but this is where it's good to lean into Grant's philosophy that the frame is the bike and the paint is a thing that kinda protects it and gets scratched. 

For future efforts I would recommend going slow and only tightening until it seems fairly snug. I've found (to my surprise when I first learned it) that derailleurs stay stable without being super tight. But buddy I scratched a lot of paint before I learned this!

Joe Bernard

[Nick Payne]

That surprises me. I've been fitting band-on front derailleurs for about half a century, and can't recall ever even damaging paintwork, let alone denting a seat tube. Mind you, 4Nm is quite a lot - I'm rather surprised that the marked setting would be that high. I've never used a torque wrench on an FD clamp when assembling a bike, but it doesn't need anything like that much force applied to the pinch bolt to hold the derailleur in place. After all, the handlebar clamp bolts on threadless stems are usually marked as 5Nm; that's sufficient to hold the handlebars in place, and the rotational force on a drop handlebar when you've got your weight out on the brake hoods is many times greater than that on an FD.

The other possible problem might be your torque wrench. If it's a torque wrench that goes up to 25Nm or 30Nm, then it's quite likely to have substantial error at low settings.

Nick

[David Hallerman]

Dunno about 4Nm being quite a lot. Just earlier this week I installed a new, early 21st century Campagnolo front derailleur. And the multi-language instruction sheet put 5Nm as the target torque for the clamp.

Dave, who prefers Nm over the other torque metrics because hey Isaac Newton

+ + +

Hudson Valley NY

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[Thomas Lawn]

This is maybe the biggest downside about torque specs is that it's easy to lose the natural "hey, I wonder if this is tight enough?" instinct and go straight to "well it says put it at 9Nm so *crack*!"

Firstly, the published torque for clamps is not a "target number" to hit, but actually a maximum. The object being clamped will also have a maximum value, and for a thin-walled butted seat tube, it may well be less than 4Nm. For front derailleurs, just tighten until it gets snug and give it another 1/4-1/2 turn. It should be completely immobile and very easy to tighten down using the short end of an allen key or p-handle wrench. If you have to use a long arm to torque a derailleur band, it's likely that something bad is happening. Don't lubricate the clamp because that will require more clamping force to resist moving, but you can grease the threads of the bolt.

The good news is that there are millions of steel bikes out there with slight dimples on their seat tube from front derailleur clamps and they're completely fine. I have a frame with two dimples because the Incredible Hulk installed the derailleur too high or too low the first time. It's also nearly impossible to detect those dimples unless you're specifically looking and feeling for them, so you'll likely forget they're even there in a year or two.

This may get me some push back (although perhaps not from this crowd) but I generally do not use a torque wrench on anything involving a metal to metal interface with a few exceptions (Shimano HT crank pinch bolts being the most common). With things that are common on Riv bikes like quill stems and threaded headsets, most of these components were designed before every mechanic had access to a torque wrench and have no meaningful torque spec because the limiting factor is rarely the stem and more often the steerer that fails. These components, and square taper cranks, just need to be torqued a lot but not too much, and finding that by hand is pretty easy if you go slow, evaluate what you're doing and the effect as you go, and don't use a wrench that is too big for the job!

Cheers,

Thomas in Portland, OR

[George Schick]

Good comments.  Another thing about torque wrenches - IIRC, the ones with the moving indicator-needle-along-a-scale (not the ones that "click" when target torque is achieved), need to be held in a specific way with one's index finger on the wrench arm as a nut or bolt is tightened or you'll get an inaccurate reading.  At least, that's what a mechanic told me once.

[JP]

Thanks again all - so far i've had very positive experiences taking apart and redoing this bike (i wanted lower gearing and changing the crank and BB magically did that) I feel like while a bike that comes new from Riv is built up much more cleanly and proficiently than I would do - there becomes a crossover point where the ability to readjust things and replace the odd thing leaves me with a better riding bike than something I'm too scared to touch.

This is the first bruise - and i feel like i can reduce the risk better in the future - even though i have a nice clicky, but non-moving-scale 3-6 NM wrench for the job, i probably wouldn't have overtightened if i would have just use my own feel.   I was worried about under tightening and then the cable pulling the clamp screech down the tube at the other extreme.

Finally I can't see any reason to blame the part per se (the 28.6 problem solvers clamp) which was another of my concerns!

Best,

JP

[Christopher Cote]

I don't know what you used for a torque wrench, but I find the click-type often need to be used a click or two after being set, before it will click over at the set torque. Internal sticktion or something like that. I like to set the torque wrench, and then test it on some bolt that I know is torqued way more than the current setting. The swingarm bolt on my DR650 motorcycle is often used for this, but I'm sure you can find something handy if you don't have one of those in the shop.

Chris

[Garth]

I've used a torque wrench for cartridge BB's and that about it. I was given one, that's why I used it. Otherwise I never use one. What "the numbers" never have is intelligence. I found this article which gets to the gist of why I've never used for anything else on a bike. Unreliability. 

https://james-p-smith.blogspot.com/2011/05/torque-wrenches-and-bicycles.html

[David Hallerman]

Actually, the instructions for my Campy FD clearly say to “fasten the tightening bolt to the frame, torquing to the following values…”

The phrase “to following values” describes a target, not a suggested max. Now maybe other component companies say their Nm number is the max for that part, but until then, it’s more useful to rely on the company that made the part than other sources.

Dave, who thinks some torque numbers are conservative because the manufacturer doesn’t know if you’re using more fragile carbon or more robust steel

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[Joe Bernard]

Another issue is the Problem Silvers website lists 3.5nm for that clamp. The product may have come to the OP with outdated instructions and those instructions may be outdated because someone told the company it pinched a tube. 

Joe Bernard

[Thomas Lawn]

Despite whatever the (translated from Italian) instructions say, I’ll still go with my experience and understanding of the inarguable fact that the derailleur doesn’t need to be torqued to that value to stay put or work properly. 

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[George Schick]

As a bit of a side issue, but still relevant to the conversation, that's the reason why open-end wrenches, box-end wrenches, combo wrenches, etc. come in various lengths, becoming shorter as the nut/bolt size becomes smaller - they're made that way with the assumption that only a reasonable amount of torque can be applied to the wrench given its length.  In like manner, if one has the need to use a ratcheting wrench instead of one of the above, a smaller/shorter ratchet should be used for the smaller sockets (1/4", 3/8", 1/2" drives accordingly).  Unless, you want to be like my father who white-knuckled almost everything he did and would frequently strip threads or round off bolt heads.