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One of the many great things about bmx bikes is that they're really easy to work on. For the vast majority of repairs you'll need only allen keys and a ratchet with 15mm and 17mm sockets. If you have pegs you’ll need an extension, and it’s also good to have a pedal wrench. As is the case with any bike, I recommend investing $3 on a lifetime supply of general purpose grease.
Let's talk about a few repairs which are needed most often on BMX bikes.
Even on a new bmx you may have issues with your bars moving when you land. To fix this, first remove the bolts clamping them to your stem. Then, clean all the areas that make contact as good as you can, which will prevent any debris or loose paint from allowing the bars to move. Before you put everything back together, grease the threads on the bolts so that you can get them really tight without any issues. When reinstalling the handlebars, most riders make them about parallel with the fork, but this can be tweaked to your liking. Tighten each bolt a little at a time, so that everything sits flat and even. You’ll want to use a calibrated torque wrench to apply exactly 8 newton meters of force to each bolt. I’m kidding, it’s a BMX, so tighten the crap out of them.
Next is the headset, which consists of the bearings in the head tube. A loose headset is common in BMX because the bike is subject to hard landings and crashes. A loose headset can cause an annoying rattle and even result in damage to your frame and bearings. To test for a loose headset, you can stand in front of your bike and apply force to your bars in different directions. If you feel anything besides steering, it’s probably your headset.
To correct this, loosen the pinch bolts on the stem evenly until your bars can move independently of the fork. Then tighten the bolt on the stem cap slightly and test your headset again. Don't over-tighten this bolt, as it could make it hard to steer, or crush your bearings. You should be able to steer easily and freely. Once the headset feels right you can line up your bars and tighten the pinch bolts again.
With all the abuse that BMX cranks take it's common for them to develop a creaking sound. This usually means the spindle wasn't greased properly during installation. Unlike road and mountain bikes, BMX cranks don't usually need a crank puller for removal. On these cranks we’ll loosen the pinch bolt and remove the cap at the base of the crank. Getting the crank off the spindle may take some effort if you've been running them without grease for a while, but these ones come off pretty easily. Make sure there's a light coating of grease on the spindle and reinstall the crank arm by tightening the cap first, and then the pinch bolt. Do this for both crank arms, and the annoying creaking should be gone. Any other sounds, like popping or grinding are probably your bottom bracket, and we won’t be going over that in this video.
Like most single speed bikes, the chain tension on a BMX is set by positioning the rear wheel in the slotted dropouts. Some people have trouble getting the chain tension right, and the rear wheel lined up properly, but it's actually pretty simple. First, let's talk about chain tension.
When you turn the cranks and observe the chain on a BMX you'll notice that the drivetrain will have a "tight spot" and a loose spot. The better your parts, the less the disparity between these two extremes. We'll get back to this in a minute.
To adjust your chain tension, loosen the axle nuts and move the wheel within the dropout. When you get it to a good spot, tighten just the drive side lightly. Now turn the cranks and check the tension. If it's harder to turn the crank when you get to the tight spot, the chain may be too tight. This can stretch and weaken the chain, plus make it harder to pedal. To correct this, keep the crank on the tight spot and loosen the nut on the drive side a little. The tension on the chain should cause the wheel to move inwards slightly, and then you can retighten the nut.
Now it's time to line up your wheel. Usually the wheel will be almost perfect at this point, but if not, apply some pressure with your thumb to get the wheel into the right spot, and tighten the other nut until it stays in place. Now test your chain again and you're done. You should also grease the threads on the inner part of the rear axle so the nuts can be tightened more easily.
So those are a few of the most common repairs you should be able to perform on your BMX. Most others require the same tools and some common sense. Bmx bikes can handle all sorts of abuse, as long as you’re willing to tweak things back into place every now and then.
In the next video, we’re going to learn the first BMX techniques you’ll need to know.
29 сен 2024
