Bicycle Mechanics - correct way to tighten handlebars?
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09-26-11, 09:48 AM
I have only a general mechanical background and knowledge, nothing specific to bicycles so I have this question.
when the bike was a month or so old the handlebars started "creaking".. then I noticed one of the allen screws was gone, the LBS replaced it and snugged them up and a week or so later the bars started creaking again. this time I snugged them up, trying to tighten each one as equally as I could but after a 40 mile ride on chipseal they are creaking again and one of the allen screws was very loose..really getting tired of driving 10 miles to the bike shop everytime I need a screw tightened.
I (we) must not be doing something correctly, what's the proper way to tighten the bars?
Assuming a one piece 4 bolt front plate, the key is not to twist the plate. Assemble the plate and pre-tighten all 4 bolts until they just make contact, being sure to leave a gap at both the top and bottom. Now as you tighten, remember that both top screws and both bottom screws work as pairs, so keep them matched by tightening them to matched torque, or number of turns. Top/top, bottom/bottom. Work by degrees so you never get far from the matched torques.
09-26-11, 11:24 AM
Not all stems and bars are an ideal fit either. A set of bars that work one or more screws loose is a suggestion to me that your bars are flexing around in the clamp. First off are there two or four bolts on your stem? In any event with the bolts just making contact and a few oz of torque try to wiggle the bars. If you detect a bit of looseness when lifing and pressing up and down on the grips in a seesaw manner so that the bars seem to be hinging and swinging a bit I'd say you're a candidate to try a packing shim of pop can metal around the bar. Cut a long strip that is as wide as the stem saddle and long enough to wrap fully around the bar with a small 1/16 inch gap between the ends. Situate the gap at the top or bottom where the cap and stem have their own gap. Now tighten down the cap until it just contacts and put a very few oz of torque into them. Ckeck to ensure the wobble is gone and the bar fits the stem with a solid seating.
NOW tighten the screws going back and forth upping the torque a few inch oz at a time until you're up to the correct torque. In the case of a 4 bolt cap this is even more important so that you end up with the cap not being twisted by uneven torque.
As mentioned grease the threads as well to avoid future corrosion issues. And lightly grease the shim on both sides as well. The grease allows everything to slip a little and find the best fit. It also allows the torque you apply to produce more tension in the bolts. And finally be sure you're torquing them hard enough. Usually folks overtorque small fasteners such as found on bicycles. But it sounds like you may be one that is under torqueing them. With an L shaped allen key and the usual 6mm stem bolts with two fingers at the long end of the key and your thumb on the elbow as a fulcrum you should be using enough torque that your fingers get an impression from the arm of the key that lasts a few seconds but not torqueing so hard that the arm of the key digs in and creates any slight pain. Basically around 4 to 5 ft-lbs.
09-26-11, 11:59 AM
diver88: Beside the suggestions to grease the threads and to progressively tighten the bolts, I'd suggest you obtain and use a torque wrench and torque the fasteners to the manufacturer's recommendations, which are often marked on the stem itself. Properly-torqued fasteners should not loosen under normal use, but blue Loctite can also be used as a belt-and-suspenders tactic. Torque wrenches can be had dirt-cheap and are an investment which will last a lifetime. If you move up to carbon components they are a must and if you save damaging one component due to improper torque, or avoid an injury, the tool will have paid for itself.
09-26-11, 03:07 PM
So what's the material of the handlebar? And material on the stem? In my experience, the cheaper steel stems, especially threadless ones, often take some time when new to to fully tighten. It seems like it's a period of work hardening, and it takes up to 100 miles for the steel tabs on the stem to stiffen up and stop flexing so much. But I get some flex while riding, and then I find the bolts have loosened. I resorted to using a red marker on the nuts of one stem to record the orientation of the bolt to see if it moved. And surprisingly, it did not. Instead, it was the steel yielding. And after about a month of riding, I was able to tighten that stem finally and not have it come loose.
Coming loose is one problem. The other is creaking noise. With steep bars and steel stem, little to no noise, even when loose. With aluminum bars, however, I do get creaking, and it varies. Some bars, with an added collar that doubles as a shim (older 25.4mm clamp bars) creak more. The newer bulge formed bars don't creak much at all, except when using an aluminum stem.
And the aluminum stems that seem to make more noise are the ones with soft top plates that keep deforming and can't seem to even withstand 6 - 10 ft-lbs of torque. Most aluminum alloy stems with a pop-top plate and either 2 or 4 bolts will recommend 5 - 10 ft-lbs of torque on the bolts. But I find that some have quite soft top plates that deform underneath the bolts and have small or no ridges inside the clamp recess on the stem or the pop-top. And so the bar will squirm while clamped and so I think this is the cause of creaking. I rarely get any complaints about cro-mo flat bars (e.g. for downhill) with alum. alloy stems. I think the cro-mo is much harder and so you can torque down on the clamp bolts forcing the softer aluminum to conform securely and tightly around the steel collar. I grease the bolt threads to avoid seizing of steel bolts into aluminum threads, as others recommended, and then only use around 8 ft-lbs of torque and check them after the first few rides. If it holds after a week, it's likely to hold for a good long time.
09-26-11, 04:51 PM
"Some bars, with an added collar that doubles as a shim (older 25.4mm clamp bars) creak more."
I've quieted some bars like that by removing the bar, running cyanoacrylate (Krazy) glue into the gap between the bar and the collar, and re-mounting it after the glue has set.
09-27-11, 09:28 AM
thanks for the replies, they all make sense.
2010 Trek 2.3, not sure but I'm guessing the 4 bolt plate and stem are aluminum, along with the bars.
I need to find my torque wrench, find an adapter for the allen wrench, find the torque value for the plate/stem (unless the 5.2N is a reference to that) and just get it tightened better. I also need to check the seat post bolt torque because what I can assume from the replies here anything made of carbon fiber is very dependant on the correct torque. I saw the LBS salesman just tighten that with a pocket tool and he was sure it wasn't CF but Trek say's it is.
09-27-11, 10:21 AM
"I also need to check the seat post bolt torque" Make sure you use carbon assembly paste (Tacx, FiberGrip, FSA or the like) on your carbon seat post. Any, yes the torque wrench is a must.
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