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Drilling and Tapping


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Thread Repair Options
Drilling and Tapping

Tools required to tap threads.

John H Glimmerveen Licensed to About.com

As classic bikes get older, the threads holding components together often become worn. For example, spark plugs could have been replaced many times since the bike was new and sooner or later the threads will become inadequate to hold the plug at the correct torque.

Threads in aluminum engine cases are also prone to damage or wear due to continuous use or over tightening.

In most cases damaged threads can be repaired, or more precisely, replaced. A damaged casing thread can be repaired using one of four methods:

  • Heli-Coil® wire repair
  • Tapping the threads deeper
  • Re-tapping to the next size up
  • Welding

Where re-tapping to the next size up is the logical repair, the mechanic must consider the strength of the repair. For example, the most important consideration is how much material will be left around the threaded hole. If the resultant threaded hole will leave only a small amount of material around the hole, the mechanic will have no other option but to have the casing professionally welded.

Tapping a thread is relatively simple. The mechanic will need:

  • A powered drill (electrically, battery or air powered)
  • A high-speed-steel or high carbon drill bit
  • Tap set
  • Tapping lubricant

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