Difference between revisions of "Internal Maintenance"

Revision as of 14:24, 24 November 2010

The Advanced Maintenance class is a hub overhaul intensive class covered in 3 sessions.

• Day 1: Headsets
• Day 2: Bottom Brackets
• Day 3: Hubs and wheel truing

Outline of the syllabus to follow shortly. The current rough syllabus can be accessed on Googledocs, here.

Bike Kitchen Advanced Maintenance Syllabus.

The fundamentals of bearing systems:

Bearings on a bicycle allow the parts to rotate relative to one another. The headset allows the fork, the bottom bracket allows the cranks, and the hubs allow the wheel to all turn smoothly while riding.

Adjustable type bearing systems use two opposing races which can be moved relative to one another. If the adjustment is too tight there will be too much pressure on the bearing surfaces and balls and the system will quickly wear out. If the adjustment is too loose there will be movement or "play" between the parts. This will cause a knocking in the bearing surfaces and again they will wear out prematurely. Generally, the bearings should be adjusted as loose as possible without play or knocking in the system.

Day 1, Headsets:

The headset allows your bike to turn smoothly.

· Headsets that are adjusted too tight will create too much friction between the bearings and the races. This will cause the steering to be rough, and can make the handlebars difficult to turn. Ultimately, a headset that is adjusted too tight will prematurely wear down the bearings and the races.

· Adjusting a headset too loosely will result in knocking of the steering column against the races. This in turn applies the force to the headtube of the bicycle. This knocking can actually cause the headtube to become ovalized. Once the cups and headtube have become ovalized, you cannot make a proper adjustment to the headset. Attempting to tighten the headset will only cause the bearings to bind since the races are no longer round. For this same reason it will also be impossible for headset cups to be replaced with properly fitting cups.

Generally, the bearings should be adjusted as loose as possible without play or knocking in the system. This will allow for the smoothest possible movement between the bearings and the races, with as little friction as possible.

1. Anatomy of a headset. Present anatomy by showing a complete headset. Explain difference between threaded and threadless.

Threaded headset: The top cap and locknut screw onto the top of the fork (steering column) of bicycle. Tightening or loosening the lock nut will tighten or loosen your headset. Can only be used with a threaded fork. Typical on all older road and mountain bicycles. These usually have a diameter of 1” on road bikes, and 1 1/8” on mountain bikes.

Threadlesss headset: These have become somewhat of the norm on modern road and mountain bikes, and have been the standard for a long time on BMX bikes as well. They are used with a threadless fork (hence the name), and the top cap, rather than screwing onto the fork, has bolt through its center that screws into a nut nested inside of the fork. The adjustment of this kind of headset is made by tightening the bolt which applies pressure to the bearings on the races. Size is typically 1” or 1 1/8” on road bikes (the latter being applied to more modern bikes), and 1 1/8” (and occasionally 1 ¼”) on mountain bikes.

2. Checking headset for wear and overhauling: Depending upon type and quality of headset (loose bearing vs. cartridge bearing vs. King etc.), headset should be checked periodically for wear and dirt build up, and overhauled (or cleaned and repacked) if necessary. The wear on the bearings and race surfaces will affect how well your headset works. Build up of dirt will contribute more quickly to wearing down these parts.

a. Discuss tools used for headset adjustment and removal/installation. Focus importance on using proper tools for top cap on threaded headset to avoid stripping outside of cap.

b. Remove top cap from a headset (currently installed on a bike) for class and discuss overhaul process using this headset/bike as example. Demonstrate how to properly remove the fork, retainer rings, and bearings, and how to carefully place everything aside to perform an overhaul. Focus importance of keeping bottom bearings w/ lower race and upper with upper. Explain why this is important (wear patterns, especially on retainer if present). Maybe have a project bike set up in the shop so that we can fully pop the cups out and the crown race off of to show a full demo of removal and installation? Maybe use my own…

c. Have class remove their top caps and forks, and carefully remove their bearings to begin overhaul

d. Class now has their headset guts laid out in front of them. Discuss how to properly clean:

                                         i.    Use lint free rags 

                                        ii.    Check for pitting or rust in races and bearings 

                                       iii.    Throw out bad bearings 

                                       iv.    How to deal with bent retainers (to replace or to re-pack with free bearings), 

                                        v.    Importance of using proper bearing size 

                                       vi.    how to pack free bearings with no retainer 

e. Class will clean and repack headsets (this will take a while)

3. Headset Adjustment: Now everyone’s headsets are re-assembled but not properly adjusted.

a. How can I tell if my headset is too lose or too tight? If too loose, a knocking will be present when applying the front brake to the bike and pushing it forward. If too tight, the steering column will be difficult to turn, or will not turn smoothly.

                                         i.    Show how to check for knocking by applying front brake and turning front wheel 90 degrees. Re-emphasize importance of proper adjustment. 

                                        ii.    Demonstrate how to check for grinding of an over-tightened headset (feel headtube for vibrations), or a detent in the center of the headset to observe a worn headset (bike in stand and on ground). 

b. Explain and demonstrate a threaded adjustment.

                                         i.    Discuss compensation in adjusting due to tightening lockring. 

                                        ii.     When adjusting, adjust first on the stand, and then check and fine tune the adjustment with the bike on the ground. 

c. Explain and show the function of the threadless headset as the stem and top cap work together to apply pressure to the steering column, and perform adjustment. This adjustment occurs more easily on the ground than in a stand.

d. Questions, and adjust!

DAY 2, Hubs and BB’s

Hubs and BB’s function using the same principles as the headset. Friction is created between the bearing surfaces and the races by tightening down one side of the hub or bottom bracket on a threaded surface. As with the headset, the hub and BB will function best when adjusted as loosely as possible with no knocking present.

“We are not going to perform the overhaul or adjustment of the BB. Instead we will focus on the overhaul and adjustment of hubs. They employ the same principles and techniques for overhaul and adjustment as the BB, and we have plenty of tools available for everyone to practice this skill”

Present overview of BB’s instead, and quick demo.

BB’s (Bottom Brackets): BB’s come in two types; cartridge and loose bearing.

Cartridge BB: cartridge BB’s are cheap, reliable, and require virtually no maintenance, and zero adjustment. These are referred to as “one-piece” BB’s and are comprised of a large, complete BB on a single spindle. The spindle has a “fixed” cup attached to one side (usually the right), and a removable ring or “cup” that fits onto the other side (show a cartridge BB to class). The BB fits into the BB shell of the frame with the fixed side threading into the drive side (right side) of the bike. The loose cup or ring threads into the other side of the BB shell to hold the BB tightly in place. Because the bearings are internal and cannot be accessed or adjusted, when they do finally wear out, the entire BB must be replaced. They can be purchased relatively cheap and usually last around 2-3 years or more, depending on use.

Common Cartridge BB problems:

1. Creaking while riding: this is usually due to the non-drive side cup having come a bit loose. When this happens. The force from pedaling will allow some movement in the shell (imagine a see-saw), and the creaking occurs. To fix, tighten the non-drive side cup. You can also use locktight (rather than grease) to install this cup, reducing the likelihood of it coming loose. Some times when a BB is installed for the first time, the manufacturer will recommend using grease, and then re-tightening the cup again after a few days of riding.

2. Plastic BB cups. Some cartridge BB’s are made with plastic instead of aluminum cups. If over-tightened they can crack, causing a creak when the cranks are pedaled.

Loose bearing BB (Show complete loose bearing BB to class while explaining.): These function the same way as a cartridge BB in that they have a cup that threads into each side of the bottom bracket shell. These are different because the BB exists in pieces much like a headset, and the pressure exerted on the bearings is adjustable. There is a spindle, 2 cups, 2 bearing sets, and a lockring to each BB. Each cup has a bearing race machined into the inside of it, and the spindle is machined with a cone on each end. When the BB is put together, the bearings sit in each side of the BB, each set nested in between the cone on that side of the spindle, and the bearing race inside of the cup. This type of BB can last for decades with proper maintenance. Like headsets, this type of BB should be checked periodically for wear and re-greasing.

Loose bearing BB adjustment: The fixed side or drive side cup is threaded in first, all the way. The loose or adjustable cup that threads into the shell on the opposite side can be loosened or tightened, controlling the amount of pressure exerted on the bearings. When the desired adjustment is reached, the lockring is tightened down to hold the adjustment in place.

Loose bearing BB’s can use a variety of different tools to adjust the cup depending upon the manufacturer or age. They all require tools that are specific to the BB, and they cannot really be adjusted properly without the use of these tools.

Discuss crank removal, crank pullers, and demonstrate a crank removal and BB adjustment. Class will not over haul BB’s.