On a standard bike here is what you'll most commonly fix.

1. Preface
2. Introduction to Basic Inspections
3. Adjusting Cones (And Regrease Hub Bearings)

1. Preface
Preface: This document is just a list of routine maintenance operations. A full description of the parts involved is in my document "How a Bicycle fits together". There are also Youtube videos for most operations.

In theory one would have a fixed schedule to inspect every item. However in reality I'm just going to mention a few things you should check periodically.

The scope of maintenance I'm talking about is where routine parts that wear need to be replaced. I'm not talking about upgrades, such as changing what size of cassette you use.

These would be the things you would examine if you were buying a used "standard bike".

2. Introduction to Basic Inspections
In talking about how often things need to be inspected or replaced, it depends on how often the bike is being ridden. Below is a schedule for a bike ridden a couple of times a week. If that bike has been sitting for weeks, you need to check certain things such as tire pressure and chain lube.

This is also a quick list if you just bought a bike, or it's been sitting for years.

    Item                  Interval
---------------------------------------
   Tire pressure check    2 weeks
   Chain Lube             Every 3rd ride
   Chain replace          Every year or two (200 rides)
   Cassette Replace       every year or two (200 rides)
   Brake Adjustment       every few months 
   Brake pad Replace      every year
   Cables                 1-2 years 
   Seat Post movement     every year   
   Check Wheel Bearings   every year  
   Head set clearance     Every year 
   Handlebar stem         every year    
   Wheel bearing Lube     every 5 years 
   Freehub                every year   

1. Tires
    You typically check your tire pressures on a bike every week or two. In a week, they will typically drop from 80 PSI to 70 or 65. You can make a quick check of inflation by squeezing the tire with your thumb and fingers. If there is any give, the tire is soft. The squeeze test is usually good enough. On my road bikes (35mm tires), I aim at 70 or 80 PSI, and let it go down to 50 before re-inflation. Below 40 the bike really drags, and doesn't steer properly.

2. Chain Lubrication
    You should make sure the chain is always well lubricated. Usually this means squirting a bit of oil or wax based lubricant onto it before any full day ride. The most standard is to use various types of oil, but there are also wax based lubes. If riding in wet conditions, there are thick oils that stick better than thinner oil. Problem with all oil is it very soon picks up dirt and becomes horrible black grease. To get around that problem, you can use wax based lubricant. This does not pick up dirt, but you have to apply it more often. I've been using wax based lubricant for years now, and if I'm going out for a full day ride, I usually apply more lube.

3. Cassette and Chain Replacement
    Replacing the Cassette and chain is the most common replacement, much more frequent than tires or tubes. If the bike is ridden daily in rain or grit, the cassette and chain will wear out each year. There are two strategies:
    1. Don't replace till it actually starts skipping gears
    2. Replace chain as soon as it fails the "stretch" test

   Chains don't really stretch, what happens is the grit eats away at the bearings on each link, such that the chain becomes elongated. There is a special tool to test chain wear called Park Tool CC-3.2 Chain Checker. It has two prongs about 15 cm apart that stick between the rollers of your chain. If you can push the prongs in, your chain needs replacing. However on our chains, this tends to happen quickly, within months of each new chain, so we often ignore it.

4. Brake Pad Adjust and Replace
    Both disk brakes and rim brakes require adjustment, and the pads on both tend to wear out every year. With rim brakes, check every week or two that the brake is not rubbing on the tire. With both types of brake, there seem to be quite a price range, with some pads 4 times the price of others. I am currently experimenting to see just how much worse the brand name disk pads are from the generic ones. For a downhill mountain brake,

5. Cable Adjust and Replace
    You can expect to replace brake cables and shift cables every year or two. It is worth carrying spare cables on any multi-day tour. Particularly prone to failure are the "short pull" cables for cantilever rim brakes. They fail more often because the force in the cable is higher. The cables on a standard steel frame bike are external, as opposed to cables that are interior.

6. Check Seat Post
    Every few months, loosen the seat post (with the quick release) and make sure you can slide it up and down. Apply a thin layer of grease if necessary. It is quite common for seat posts to corrode a bit and seize into place. Once they seize, it is very difficult to free them, and many shops have been defeated.

7. Adjust Cones
    The "cones" adjust the wheel bearing clearance. If they are too loose, the wheel will wobble, and if too tight, the wheel will bind. The cones are two conical shaped nuts on which the ball bearings ride.The clearance of the cones should be such that the wheel rotates freely but does not have looseness. The old test of "free rotation" is that the weight of the valve stem should be sufficient to cause the wheel to rotate.

   You should check that your wheels don't have excessive play every few hundred km. Wheels can go for years without needing new grease, but it is probably a good idea to regrease them every 5 years. Check the cone adjustment every few months. See separate chapter on cone adjustment.

8. Freehub Cleaning or replacement
    A quick check of the freehub is to make sure you hear the tick..tick..tick as the wheel lcoasts. The freehub is the core of the cassette system on the rear wheel. Normally these never need maintenance, but they can get gummed up or the springs or teeth wear out. If gummed up, soak it in solvent, then reapply light oil between seams. Freehubs are not designed to be taken apart. See Park Tools Website

9. Handlebar Stem
    Like the seat stem, check that the handlebar stem is not getting seized. With a quill type, loosen the bolt and then rotate the handlebar within the headset.

10. Head Set Bearings
     I've had to adjust the clearance of my head set about once a year on a couple of my bikes. The way to check it is to put the front brake on, then rock forward and back. If you feel any clearance, you need to adjust. This takes two wrenches. There are two types of headset:

      Threaded forks (Quill type Stem inserts into inside diameter of fork
      Threadless forks (stem clamps on)

    How and Why to Adjust the Headset on your Bike
     This "Maintenance Monday" video shows how to adjust Threadless Forks with sealed bearings.

    Park Tools
     Excellent video shows the difference between threaded vs threadless headsets.

11. Chain rings
     In theory, the front chain rings can become worn just like a cassette. However because it has many more teeth, it is rarer to replace them. These days you may as well buy a whole crank set as to try and find the one ring you need. On my bikes they originally had fancy aluminium chain rings, but on 2 of my 3 bikes, I've converted to inexpensive Shimano steel cranksets costing less than $100.00.

12. Bottom Bracket Bearings
     The main crank bearings are in the part of the frame called the "Bottom bracket shell". These bearings are often confusingly referred to as the "bottom bracket". In the old days before 1990 sealed bearings, an annual maintenance procedure was to take apart the regrease these. And also check for correct clearance. But nowdays, most bikes have a sealed bearing unit. Surprisingly enough, these fail more often than a properly maintained separate unit.

3. Adjusting Cones (And Regrease Hub Bearings)
The most standard type of hub bearing is the tried and true cup and cone system. Although these days there are specialized hubs using sealed cartridge bearings, Shimano has stuck with the cup and cone system. Cup and cone are better than sealed cartridge bearings because the clearance can be adjusted as they wear. And the ball bearings can be larger. And you can repack the grease.

Adjusting the clearance in the cones is simple. Just remove the wheel, and use two wrenches to undo the lock nut on one side. Then move the cone. You don't need to remove the axle. However, if you want to re-grease the hub, you'll want to remove the axle. To do that, you remove the cone on one end and slide the axle out. You'll probably have to remove rubber and metal dust covers on both ends. These vary from hub to hub.

 The "cones" are two tapered nuts that thread onto the axle, and form one side of the axle ball bearing mechanism. The other side of the bearings is the ball "race" which is built into the hub. By threading the cones inward, you squeeze the ball bearings. The correct clearance is usually to turn the cone all the way in, then back off a 1/4 turn. Each cone has a washer and a lock nut. The cone is held in the correct position by twisting the lock nut against the cone. This is done with two wrenches turning against each other. The cone nut is usually 14 or 15mm. It requires a special thin wrench to hold it while you use a larger wrench (17 mm) to turn the lock nut.

The problem is that sometimes when you try to loosen the lock nut on either end, the axle turns with it. Although the cones on both ends can be removed, for normal servicing you only remove one end. One end is usually a bit looser than the tight end. Thus by putting the tight end into a vice (or vicegrips) you can effectively prevent the axle from turning. This allows you to unthread the lock nut from the axle.
 

1. Remove cone
    - there is a cone and locknut on both ends of the axle, but one side is usually looser and easier to get at than the other.
    - remove the rubber dust cover
    - Put the tight end into a vice
    - Use two wrenches to loosen the lock nut on the "adjustment end". Actually if the tight end is really the tightest, all you need is one wrench to loosen the lock nut?
    - remove the lock nut, and then the cone. The axle should remain fixed.
    - once the cone is removed from one end, you can slide the remaining assembly (axle + tight end) out. You can now regrease or remove the ball bearings.

2. Install adjustment cone
    Start with the axle assembly with the tight cone and locknut installed (they have never been removed.
    - insert the axle thru the hub
    - Hold the tight end in a vice or vice grips
    - thread the cone you had removed back onto the axle till it is finger tight, then back off 1/4 turn.
    - thread the lock nut onto the axle, finger tight to the cone
    - use two wrenches to lock the locknut against the cone. The axle should not move

3. Assemble Axle with both cones
    (rebalance cone spacing or change the axle) If you have the cones on both ends of the axle removed, when you put it back together, they need to be balanced. (About 4 threads showing) So what I did was the following:
    - put the cone on one end to approx the right position
    - hold the axle in the vice and put the locknut on so it is almost to the cone
    - with two wrenches, still in vice, tighten the locknut to the cone. Really hard because this end will have to hold the axle when we do the other end. Vice not really necessary. It doesn't matter which one moves because it is a very small distance. If the axle moves with the locknut, the cone is moving out slightly. If the axle moves with the cone, that is what we want anyway. Now we have the axle and one fixed end.
    - put axle into hub
    - put vicegrips on the fixed end. That prevents the axle from moving.
    - thread the cone on the other end, finger tight, then back off 1/4 turn
    - hold the cone with cone wrench and thread the second locknut on. The axle will not move because it is held with the vice grips. Or could do this with the fixed end in the vice.
    - tighten the lock nut to the cone. (Not quite as tight as the first one) The axle can't move because the tight end is in the vice and holding the axle.

    

4. Video - How to Adjust Cup and Cone Wheel Bearings on your Bike
    This is a good video. He uses a vice to keep the axle from turning, but he seems to hold the axle itself, whereas I've often found I rely on being able to hold the axle by the jammed nut-cone assembly.

5. [a href=https://www.parktool.com/en-int/blog/repair-help/hub-overhaul-and-adjustment?srsltid=AfmBOore4Vcwo7Bs4z0pronCUqXdZzAQBRJJXFSxgcJGjDhXwvGnxYIJPark Tools Article[/a]
    This description has a very good diagram showing the cone and cup design. Some of the description goes overboard. He says to iterate toward perfect adjustment 1/32 of a turn. But I have found that simply by finger tightening and then backing off 1/4 turn usually ends up with minimal play and easy rotation.

6. Different size wrenches
    First thing that varies is the size of the nuts.

7. Hub Rebuild
     To refresh the grease in your wheel bearings, you need to remove the cone from one end,remove the axle and other cone, remove the pressed dust covers and ball bearings, and soak and brush everything to remove old grease. (Park tools says you don't necessarily remove the pressed dust covers as they can be damaged. They say you can work around them. However I found that on one hub I overhauled, it was good to remove them because there was gum and crap behind them, and you can also get at the ball bearings much more easily. Then apply new grease. Some hubs have tricky bearing seals with the cup facing outward. At first I thought they were part of the hub, but then discovered I could pop them out with a screwdriver. You don't need to remove these if all you are doing is adjusting the cones. But if cleaning and regreasing the hub, you'll want to pop them out to get better access to the ball bearings.

8. Quick Release Must be Tight
    If the dropout is not really tight, the wheel will be pulled forward by high tension in the chain. Assume the quick release is inserted such that the tightening lever is on the non drive side. On the drive side is a thumb nut, which is pulled against the cone locknut such that the quick release squeezes the chain. Fortunately both the thumb nut and the lever are concave about 2mm. The "axle projection" is the distance the axle sticks out from the lock nut. This is determined by the thickness of any spacers between the cone and locknut. If the axle projection was too long, the Quick Release would never be really tight. The distance between the lock nut and thumb nut should only be 2-3 mm, such that it will always squeeze the frame dropout which is about 5 mm thick. I had to examine a quick release and wheel to visualize this.

   The numbers below are measured on an actual wheel, and a typical steel frame bike:

   
      Frame thickness      6 mm
      Axle Projection      4 mm
      Indent in thumb nut  2 mm
      Squeeze Gap          2 mm   (4 - 2)
       
    

   In the above,the 4 mm axle rests on the 6 mm Frame. The Quick Release open is 6 mm, but it can squeeze down to 2 mm.

   What if the axle projection was the full 6mm? The system still works because of the indents in the thumb nut, which allows it to squeeze down to 2 mm less than the Axle projection. The measurements below would be ideal.

   
      Frame thickness      6 mm
      Axle Projection      6 mm
      Indent in thumb nut  2 mm
      Squeeze Gap          4 mm   (6 - 2)