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Old 09-11-10, 11:23 AM   #1
ClarkinHawaii
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Since my efforts to hijack the torque wrench thread failed . . .

OK, assembling my new Chinese carbon bike:

for the seatpost, carbon fiber sp in carbon fiber seattube, alloy clamp, should I lube the seat clamp bolt or not and what should the torque be either way??

for the front derailleur clamp, alloy clamp on carbon fiber sp, should I lube the FD clamp bolt or not and what should the torque be either way?

(no data has been provided with any of these parts)

These two items are critical as they are the only way I could really screw up this new frame' and I am in an agony of indecision . . .

Note: I have already purchased carbon assembly paste and will use it on the seatpost. Don't see much sense in using it on the FD clamp since the frame has been painted--although it would provide additional friction?? I'm also considering using a shim of old inner tube under the FD clamp so I don't have to worry about it slipping with light tightening . . . HELP!
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Old 09-11-10, 12:15 PM   #2
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You may have seen the other thread about the cracked carbon seat tube repair as well?

As I just wrote in the torque thread you do NOT need to tighten any fastener beyond what it needs to be to do the job. In your case if you cannot get a value for the clamp bolt from a few other carbon frames to use as a guide then I would suggest that something in the area of 35 inch-lbs to start. That's about a 6 lb pull at the end of a 6 inch allen L wrench. If the seat tube slips go with more. If it doesn't then that's a very safe torque value for a 5 or 6 mm screw in a seatpost clamp. If it does slip then begin going up in 5 inch-lb increments until it doesn't move. Then go a little bit more for insurance.

Here's a few links to torque tables to go by.

http://www.machinetoolhelp.com/Repai...que-chart.html
http://www.imperialinc.com/pdf/A_Fas...rqueCharts.pdf
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Old 09-11-10, 12:53 PM   #3
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Quote:
Originally Posted by BCRider View Post
You may have seen the other thread about the cracked carbon seat tube repair as well?

As I just wrote in the torque thread you do NOT need to tighten any fastener beyond what it needs to be to do the job. In your case if you cannot get a value for the clamp bolt from a few other carbon frames to use as a guide then I would suggest that something in the area of 35 inch-lbs to start. That's about a 6 lb pull at the end of a 6 inch allen L wrench. If the seat tube slips go with more. If it doesn't then that's a very safe torque value for a 5 or 6 mm screw in a seatpost clamp. If it does slip then begin going up in 5 inch-lb increments until it doesn't move. Then go a little bit more for insurance.

Here's a few links to torque tables to go by.

http://www.machinetoolhelp.com/Repai...que-chart.html
http://www.imperialinc.com/pdf/A_Fas...rqueCharts.pdf
Thank you . . .

actually the seat tube is the easier one, since if it slips it can just be tightened.

The FD clamp on the seattube worries me more because slippage could mean damaged components or accident . . . presumably the same torque as on the seatpost should do it . . .

what do you think of using old innertube shim under fd clamp?
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Old 09-11-10, 01:10 PM   #4
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I'd probably suggest more like 30 inch-lbs or equivalent in whatever units you're working in. Due to the design of the derrailleur clamp saddles it will tend to bite into the surface more easily. Or at least produce more pressure at the points of contact. Also you're working on the outside diameter of the seat tube instead of the inside diameter like with the seat post. That larger contact area will result in that much more friction for the same or less clamping force.

As for greasing the threads... you're on an island in the middle of a really big body of salt water. Rust from salt deposits is your constant companion. There isn't a fastener on your bike that should NOT be greased IMHO.

EDIT- Again the torques I'm suggesting should be tempered with a comparison to the suggested torques for some other carbon frames. Find out what a few others use and compare the suggestions for them to what I'm suggesting.

Last edited by BCRider; 09-11-10 at 01:13 PM.
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Old 09-11-10, 04:02 PM   #5
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Gee, I just use my educated hands. Never used a torque wrench on a 4-5-6mm bolt and I've had carbon bikes for the last 10 years.
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Old 09-11-10, 04:18 PM   #6
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Same here Dave. I had to stop and think about how much force I'd use and then translate it back into numbers and compare them to a torque chart to see if I was out to lunch or not....

It truly is an odd thing that as you work with bikes, cars, motorcycles or whatever longer and more often you need torque wrenches less and less other than for critical matching jobs. Newbies SHOULD buy them but at some point, if they pay attention to what they are doing much at all, they'll find themselves needing them less and less.

It should be noted that at least two of the failure/broken bits threads I've seen here over the past couple of years were due to folks that slavishly torqued their fasteners to the maximum allowable value time and again and at some point the fastener or the part just gave out due to this. As one poster in the currently running torque wrench thread said "I use a torque wrench but sometimes my Spidey senses tell me to stop early". Yes, it's important to work on developing that "Spidey sense"
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Old 09-11-10, 06:20 PM   #7
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Yeah, well, I swore I was just going to stay away from carbon altogether. But then I weakened. And I readily admit that I am intimidated by the thought of cracking something. And I don't have any other carbon bikes or know anybody who has a carbon bike to compare with. So I even bought a torque wrench. And after I use it a couple of times I probably won't need it anymore. But better safe than sorry.

Sort of like a first date. Don't want to take anything for granted.
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