Rear Derailleur Spring Tension

I've encountered a few used derailleurs that don't seem to put enough tension on the chain. When this happens, the chain can flop around and fall off the gears more easily. This can even cause "chain suck", which is when the chain doesn't release from the bottom of the front chainrings when you shift the front derailleur. My best guess is that the spring inside the pulley knuckle looses a bit of its "springiness" over the years. There's a relatively quick way to fix this, however. If you see two small holes next to the guide pulley, then you can move the spring over to the next hole to increase the spring tension. This is very easy on derailleurs with aluminum knuckles. First unscrew the small bolt that holds the cage together with a 2mm Allen wrench, shown here:

Next remove the bolt and the cage can be pulled from the knuckle. Then the spring can be gently unwound:

Notice the two holes on the bottom of the derailleur? Move the end of the spring into the adjacent hole to add more tension to the chain:

With the spring in its new position, wind the cage back until the tab on the knuckle is behind the stop on the pulley cage:

Now push the cage back into the knuckle:

And reinstall the set screw:

That's it. On higher quality derailleurs this is a very simple procedure. For cheaper ones with plastic knuckles, you will have to pry out a metal clip and drill another small hole to get the same result. I might show that procedure in a later post. Finally, if your derailleur is especially worn and dirty, you might want to check out this post about doing a full overhaul on it.

Wheel Building

In an older post I wrote about how I typically build wheels. I thought it was a bit hard to follow, so I'm going to include some pictures this time. First make sure your rim is straight, and that you have the correct length spokes (I like to use a spreadsheet called spocalc to find which length I need). Now you can start lacing the spokes to the rim:

The picture shows the first group of spokes laced to the rim. Basically you just thread a spoke through a hole in the hub flange, and then secure it to the rim with a spoke nipple. You want to skip every other hole on the hub, and skip every 3 holes on the rim (not counting the valve hole for the inner tube). Also make sure the spokes are exiting the hub on the same side, and that you lace them to the holes on the rim that are closer to the side you're working on. Once you have the first group of spokes finished you can start with the second:

The spokes from the second group be laced in the opposite direction from the spokes in the first group. Just how many spokes they cross will determine the crossing number (this wheel is a 4 cross pattern). The crossing number is actually determined by the length of your spokes, so longer spokes will have higher crossing numbers (generally a 32 spoke wheel should be 3 cross, and a 36 spoke wheel can be 3 or 4 cross, so measure your spokes with this in mind).

The spokes in the second group should also twist over the last crossing spoke from the first group as shown above. Now you can lace the remaining spokes in the second group, leaving every other hole empty at the rim:

 

Then you can start the third group. I like to start with the spoke nearest the valve hole to make sure that it's positioned correctly between 2 parallel spokes:

The rest of the third group is laced like the first group, and you should now leave every third hole empty at the rim in addition to leaving every other hole open at the hub flange:

The last group of spokes is laced like the second group. Just remember to twist around the last crossing spoke from the third group. Here is the wheel after lacing all the spokes:

Now is a good time to screw the spoke nipples the same amount on each spoke. I turn them until the threads on the spoke are just barely hidden. This allows me to tension the spokes more evenly later on. I start tensioning each spoke by one full turn each with a spoke wrench:

 

After every round of tensioning I check to see if the rim still spins true (or mostly true, since I'll fine tune it later). I can check this by putting the wheel on a bike frame and watching it wobble between the brake pads. I also have an old fork that I like to stick in a vice for doing front wheels.

To true a wobbly wheel, you need to loosen the spokes on one side of the wheel while tightening spokes on the other side:

This should bring the rim back to center. Don't get carried away, half turn increments are plenty.

Once the wheel is mostly true and the spokes have good tension, you need to stress relieve the spokes. Basically just grab pairs of spokes in your hands and squeeze as hard as you can:

If you're using new spokes, they will probably lose some tension so you'll have to tighten them up again. Basically you need to keep tightening and truing the wheel in small increments until the spokes are nice and tight, and the wheel spins true. This takes some practice (and patience), so don't be surprised if your first few wheels come out wobbly. To verify if your spokes are tight enough, you can pluck the spokes from a good wheel and compare how they sound to the ones on your wheel. Their pitch should be similar (spokes emit a higher pitch as they get tighter).

Quick Release Skewer Disassembled

So I have an old broken quick release skewer lying around and I always wanted to know how these things worked.

This one is held together with a nut so it can be taken apart:

Here are the internal parts. There's an off-center cylinder attached to the handle which turns inside that big hole in the skewer. This moves the skewer back and forth as you flip the lever. Here's a better look at the cam mechanism:

Cool.

Cup and Cone Bearings

Most moving bike parts use cup and cone bearings. This means there are ball bearings sandwiched between 2 angled surfaces which rotate against each other. In this post I'll demonstrate how these bearing pieces fit together. First is the headset:

The headset bearings allow the fork and handlebars to pivot freely against the frame. Here is a threaded headset disassembled:

The frame cups are pressed tightly into the frame's head tube, and the crown race is pressed onto the fork. The top race screws onto the fork's steerer tube to preload the bearings, and the adjustment is secured by the top nut (which also screws onto the steerer tube). There is usually a keyed washer between the top nut and the top race to prevent the headset from loosening.

Next is the bottom bracket:

This bearing allows the cranks to spin freely, and also supports the rider's weight while standing. Shown here is an adjustable English bottom bracket with a square tapered spindle:

Both cups screw into the bottom bracket shell on the bike's frame. The fixed cup is tightly secured on the right side, while the adjustable cup in only screwed in enough to preload the bearings. The lockring threads onto the outside of the adjustable cup to secure the adjustment. The cranks attach to the spindle, which is meant to turn freely inside the bike's frame.

The last bearing I'll show here is the wheel hub bearing. These bearings allow the wheel to rotate freely, and support the rider's weight. Shown here is a rear freewheel hub:

The bearing cups are pressed into the hub shell, and the cones are screwed onto the axle. The ball bearings rotate between these two surfaces, allowing the wheel to rotate freely. The bearing's adjustment is secured by a locknut next to each cone. Here is the hub disassembled:

 

In general, a good cup and cone bearing will last a very long time. You can dramatically extend the life of these bearings by disassembling them, cleaning the bearing surfaces, and reassembling them with fresh grease every few years. The reason to do this is to remove contaminants from the bearings and prevent premature wear from abrasive particles. Additionally on a very old, neglected bike the grease likely has dried up and will need to be replenished to protect the bearings. The type of grease you use doesn't matter very much since bike bearings don't get hot or spin at thousands of RPM. It's best to use whatever is on sale at your local hardware or auto parts store. Automotive wheel bearing grease and marine bearing grease are especially good choices because they are water resistant and typically have extreme pressure additives to protect the bearings against shock.