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12 November, 2006

Random queries no. 85

One of a series of genuine search engine enquiries which successfully brought visitors to the Ministry.  Can I help?

information on how to repair a puncture on a bycycle

'Bicycle', not 'bycycle'....

I suspect almost any puncture repair kit will include instructions, but here's my (utterly normal) technique:

You will need:

  • Two plastic tyre levers. Do not use screwdrivers, metal spoons or anything else likely to damage the wheel rim.
  • Latex cement.
  • Tyre patches. Just squares, circles or ovals of rubber, with plastic/paper/metal film keeping at least one side clean.
    Self-adhesive patches exist, and eliminate the need for separate latex cement. Follow the instructions on the packet. In my experience, these are for temporary repairs, and degrade, so one needs to replace the inner tube fairly soon. The technique I'm describing, with separate cement, effects permanent repairs.
  • A small block of chalk.
  • A small strip of medium-coarseness glasspaper.
These are the contents of a standard puncture repair kit. You'll also need a spanner of the appropriate size to loosen the nuts holding the wheel to the frame, unless the wheel has a quick-release hub.

Instructions

  • Invert the bike.
  • Deflate the tyre (if it's punctured, it's probably already flat). Disconnect the cable from the brake (so the brake opens far enough to remove the wheel). Undo the wheel nuts (or the quick-release lever). Remove the wheel from the bike.
  • Remove the dust cap from the air valve.
  • Insert the tip of a tyre lever between the tyre and wheel rim. Hook the other end around a spoke. Insert the other tyre lever into the gap you've created, then slide it around the rim, widening the gap until the tyre is no longer attached to the wheel. Remove the tyre and inner tube from the wheel, and remove the inner tube from the tyre. Remember the relative orientation for a moment.
  • Carefully examine the tyre for the cause of the puncture. Remove any glass, metal, thorn, etc., ensuring that the object is completely out - thorns in particular can break-off leaving the sharp tip ready to cause another puncture.
    Examine the corresponding part of the inner tube to find the puncture.

    Alternatively, partially inflate the inner tube outside the tyre. Find the point where air is escaping. I do this by holding the tube to my face, so I can feel the air on my lips. I don't immerse the tube in water to observe bubbles from the puncture; I consider it better to keep the tube dry for subsequent stages.
    Check the corresponding part of the tyre for the cause of the puncture, and remove it. The offending object, that is, not the punctured section of inner tube.

  • Mark near, but not over, the puncture with chalk. Fully deflate the inner tube. The hole might no longer be visible.
  • Roughen the surface of the inner tube over and around the puncture, using the glasspaper. The roughened area needs to be about the same size as the intended patch.
  • Discover your latex cement is in Manchester, having been borrowed to repair something entirely different. No? Just me, then....
  • Apply a thin film of latex cement to the roughened area. Only a thin film! Do not apply the patch yet. Let the cement dry.
  • Remove the plastic/paper/metal film from the inner-facing side of the patch (it's usually obvious which side is which). If it's present, leave the film on the other side of the patch. Apply the patch to the inner tube. Press down on the centre first (directly over the puncture itself), then press outwards to the edge of the patch, thereby preventing air bubbles being trapped.
  • Non-standard stage: I tend to add a little latex cement to the border of the patch, to help the edge melt to the inner tube.
  • Press down firmly on the patch, ensuring a uniform, tight seal. If you did the non-standard previous step, you might like to place the removed plastic/paper/metal film back over the patch and press on that, to prevent the excess latex cement sticking to your fingers. If so, remove the film afterwards!
  • If there is one, carefully remove the plastic/paper/metal film from the outer side of the patch, ensuring you don't damage the seal to the inner tube.
  • Grate the chalk against the glasspaper. Allow the resulting chalk dust to cover the patch and any exposed latex cement. Smooth it into the surface. This prevents the repaired tube sticking to the tyre.
  • Insert the inner tube back into the tyre. Check whether the tyre has a preferred direction of travel (there'll be an arrow marked on the sidewall) then put the tyre back onto the wheel, starting at the air valve. This can be done by hand; tyre levers are only used to remove a tyre, not reattach it.
    Partially inflate the inner tube, then ensure it and the tyre are properly seated on the wheel rim, with no pinching of the tube.
  • Put the wheel back on the bike. If it's the back wheel, ensure the chain is on the right gear ring. Spin the wheel to double check the tyre is straight and even on the rim. Tighten the wheel nuts or quick-release lever.
  • Reconnect the brake.
  • Turn the bike back over, onto its wheels.
  • Fully inflate the tyre. It should remain inflated.
  • Now wash your hands.

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