Bike Repair, 1-22-17

 

January 22, 2017  —  a  day to go down in history!  There were marches all over the country and all over the world, and here in  Ithaca, 10,000 people marched.  As Laurence and I waited for those who did not go to DC, we talked about the march and The Music Man.  “The barbershop quartet was spectacular,” I said.  “Well worth the price of a ticket.”

Two more attendees arrived, and we got down to business.  Laurence said we’d fix a flat – who hasn’t had a flat in their life? And  Laurence reminded us, as we worked on our bikes, to be aware of

  • Mechanical perception
  • Wrench feel
  • Failure awareness

Then he pointed out the fork, and the steerer tube, see below.

 

(http://www.vitalbmx.com/product)

Next, the drive train, that part of the bike (chain rings, chain, gears and cogs) that transmit power to the rear wheel.  Just so were all on the same page, cogs are technically the teeth on a gear or sprocket.  Gears become sprockets when you add a chain. The cogs mesh together and fall  into the links of a chain, this so the chain does not slip

(http://cozybeehive.blogspot.com/2012/01)

Then we have the front and rear derailleurs.  From Wikipedia, Derailleur Gears, 1-24-17: The front derailleur moves the chain side to side between the front chainrings, and it does this with the top, taut portion of the chain. It also needs to accommodate large differences in chainring size: from as many as 53 teeth to as few as 20 teeth.

The rear derailleur serves double duty and moves the chain between rear sprockets and taking up chain slack caused by moving to a smaller sprocket at the rear or a smaller chainring by the front derailleur.

Derailleurs require the chain to be in movement in order to shift from one ring or sprocket to another. This usually requires the rider to be pedaling.,

Chain-drive systems such as the derailleur systems work best if the chain is aligned with the sprocket plane, especially avoiding the biggest drive sprocket running with the biggest driven sprocket (or the smallest with the smallest). The diagonal chain run produced by these practices is less efficient and shortens the life of all components, with no advantage from the middle of the range ratio obtained.

Derailleur gears generally have an efficiency around 95%. (Wikipedia).

 

The last part of the class was spent on fixing a flat.  We use two tire levers (about $5 eachd and a patch kit called Tip Top Patch Kit ( $3-$6) . Note: Laurence declared that you are wasting your money with glueless patches.

 

First of all remove the tire by inserting the lever (spoon side – other side hooks onto the spoke) beneath the bead, which is the steel cable on the outside of the tire.  The valve should be at the bottom and you can hold the tire with your feet.  It’s very important to figure out what caused the flat so when we remove the tube, add air and put the tube to your ear, face, etc and identify the leak.  Spit is great—it’s accessible, free and it will bubble up in the leak’s vicinity.  Then using the chalk from your kit, or a marker, draw a circle around the leak.

Typical  Flats Types–

  1. Snakebite or pinch flat manifested as two small parallel lines—tires are underinflated (check pressure at least every 6 weeks, maybe more frequently) and the tubes sneaks over the rim and when you go over a bump, you produce these two tears
  2. Friction flat – the tire is old, the bead stretched, the tires move on the rim and this causes rubbing on the inner tube.
  3. Slow leak – running over glass, or a spike from a plant
  4. Blow out – beware, do not pressurize your tires about the recommended PSI, also be ware that on warm days, air molecules heat up, they move faster and therefore increase your tire pressure.

 

Snakebite flat, http://www.bikeacrossamericatips.com/?p=167– from, What You Can Learn From Your Flat Tires.

Should you change your inner tubes now and then?  Probably not, said Laurence, the inner tube is not exposed to the elements and is in a fairly stable environment.  You should note that if you leave your bike in the garage where there are motors and production of ozone, the ozone will degrade the tire rubber.

Onto the patching that leak.  First roughen the rubber with your quarter-sized piece of sandpaper then add about one sneeze (snotty) of glue.  Let it sit for a minute or two until its finish goes from glazed to matt; put on the round patch and leave the back transparent plastic on.  Wait another minute or two then pressurize the tube, but not completely.  Some inflation is desirable so the tube doesn’t slip out while you are installing it.  Put the tube over the rim and in, inserting the nozzle first.  Make sure the nozzle is straight.  Then put the tube inside the tire – one side with the bead, then the other.  Use your palms to get the tire in.  Here, I should have taken a photo of Annie S.  Make sure that both sides of the tire beads are in.

Next, inflate your tire.  Done!