Ask a Mechanic | Correct Torque Wrench Use & Another 2x Mountain Conversion Question

Welcome to our Ask a Mechanic column where our expert mechanic Daniel Slusser answers your bike maintenance questions. If you have a question for Daniel, please post it on our Facebook Wall or e-mail Daniel directly at daniel.slusser@artscyclery.com. Today’s column discusses how to avoid damage to components through proper torque wrench use and how to build a hybrid 9/10-speed 2x mountain drivetrain.

Question

I cracked the faceplate of my stem while torquing it to the recommended torque spec. The stem faceplate bolt torque spec is 5nm and I had the torque wrench set to 5nm. Did I somehow over-torque it, or is the stem defective? From: Bart 

If you don’t use a torque wrench you risk ruining your health in a failure induced crash and your high-end component.

Answer

There are a few variables involved here so it is hard to pinpoint what may have gone wrong. Your torque wrench may need to be recalibrated (always store your torque wrench set at 0nm to avoid throwing off the wrench’s calibration), or the stem faceplate might be defective as you have suggested. Other possibilities include that the bolts may have been torqued in the wrong sequence, or the torque wrench was used incorrectly by not gripping it at the handle. The most likely explanation is that you may have misunderstood the recommended torque value. What you refer to as the recommended torque spec, is actually a maximum torque spec. That maximum torque spec is figured using the assumption that both parts are from the same manufacturer and are completely free of any damage. Even when all of these requirements are met, I make it a habit to keep torque values to about 80% of the maximum limit. So, for a 5nm max torque limit I will only torque the bolt to 4nm. If you are nervous about slippage, apply carbon assembly paste to the contact surfaces of the two components being assembled in order to add a little friction into the mix.

One last point: if the threads of the bolt you are torquing are greased, you will be able to screw that bolt further into the component before reaching the desired torque value, thereby applying more compressive force than the component can handle. This is another reason why components can crack when torqued to the limit. If the bolt has a dry chemical threadlocker applied to its threads, the desired torque value can be hit with the bolt threaded significantly shallower into the component than when dry or greased. Keep this in mind when working with delicate components and you will know how to proceed safely.

Question

I have a 22/32/bash guard set up that was originally a 3×9. The new bike I am building will only take a SRAM S3 front derailleur, which were never made in a 3×9 as far as I can tell, or Shimano 2×10 or 3×10. The manufacturer of the only 3×9 front derailleur I can find for my application said it had clearance issues.

I am wondering if I can use a 3×10 front derailleur and shifter with my 9-speed chain, cranks and 9-speed cassette. If not could I just replace the chain and rings and still use the 9-speed casette with a 3×10 fd and 10 speed chain? Thank you for any insight. From: Don

Mountain doubles (2x systems) are all the rage these days but they raise compatability questions if you have a hybrid 9/10-speed setup.

Answer

I actually have some experience with that precise problem. If the bike is a Specialized, there should be an adaptor available to run a Shimano e-type front derailleur. If that is the case you should use the Shimano M665 SLX e-type double front derailleur. I ran this same derailleur with a 22-34 9-speed chainring setup and it worked perfectly. Shimano recommends using this derailleur for your 22-32 setup also.

If you can’t use an adaptor, go with the 3×10 SRAM front derailleur mated to a 10-speed chain and chainrings. The 10-speed chain will still work with your 9-speed cassette, so you are good there. I have also successfully used a 10-speed chain on 9-speed rings, so you could experiment using the 10-speed front derailleur and chain with your old 9-speed rings first. If it doesn’t work, then just install the 10-speed rings and you will be good to go.

Daniel Slusser is a professional bicycle mechanic with over ten years of experience. He holds a bachelor’s degree in business administration from HSU and a master’s degree in history from Cal Poly University. When he is not riding, wrenching, or writing he enjoys spending time with his wife and two children.

2014-03-05T16:09:36-08:00