Relocating Blown and Stripped Spark Plug Holes

Published on February 9, 2024
Duration: 15:54

Dragon Man demonstrates an advanced technique for repairing stripped spark plug holes in Harley-Davidson cylinder heads. The process involves drilling out the damaged area, inserting a custom-machined aluminum dowel, welding it in place, and then precisely re-machining and tapping new threads. This method allows for the relocation and creation of a new, robust spark plug thread without the need for traditional inserts or the risk of cracking older aluminum heads.

Quick Summary

Repairing stripped spark plug holes in Harley-Davidson cylinder heads involves drilling out the damaged area, welding in a custom aluminum dowel to prevent air bubbles, and then precisely re-machining and tapping new threads at the correct 45-degree angle. This advanced technique ensures a durable repair, especially on older, weaker aluminum heads.

Chapters

  1. 00:01Introduction and Engine Teardown
  2. 00:26Silicone Sealant Misuse Warning
  3. 01:06Ported and Flowed Heads Overview
  4. 01:42Flywheel Assembly and Lower End Rebuilds
  5. 02:08Volume of Engine Rebuilds
  6. 02:14Pan Head and Lower End Work
  7. 03:26Stripped Spark Plug Hole Problem
  8. 03:33Drilling Out Stripped Hole
  9. 03:41Machining Aluminum Dowel
  10. 04:19Welding the Aluminum Dowel
  11. 04:47Traditional Repair Methods (Welding & Inserts)
  12. 05:01New Oversized Insert Idea
  13. 06:26Welded Repairs on Older Heads
  14. 06:56Setting Up for Machining (45-Degree Angle)
  15. 07:24Finding the Center of the Welded Hole
  16. 08:15Measuring for Hole Relocation
  17. 09:06Marking the Center
  18. 09:26Locking the Table and Drilling Pilot Hole
  19. 10:11Spark Plug Hole Depth Variations
  20. 10:48Using the 9/16 Inch Drill Bit
  21. 11:09Drilling Through the Welded Dowel
  22. 12:03Tapping the New Threads
  23. 12:24Practice Recommended for Tapping
  24. 13:30Inspecting the New Threads
  25. 13:52Using an End Mill for a Flat Surface
  26. 15:01Test Fitting the Spark Plug
  27. 15:24Contact Information and Services

Frequently Asked Questions

How do you repair a stripped spark plug hole in a Harley-Davidson cylinder head?

To repair a stripped spark plug hole, drill it out to an oversized diameter, insert a custom-machined aluminum dowel, weld it in place, and then precisely re-machine and tap new threads. This method ensures a strong, relocated thread without cracking older aluminum heads.

What is the correct angle for Harley-Davidson spark plugs?

Harley-Davidson spark plugs are installed at a 45-degree angle into the cylinder head. When repairing or relocating a spark plug hole, it's crucial to maintain this specific angle for proper fitment and combustion chamber access.

Why is a dowel used when welding a spark plug hole repair?

A dowel, typically made of aluminum for this application, is used when welding a spark plug hole repair to prevent air bubbles from forming within the thick aluminum weld. It provides a solid core for the weld to encapsulate.

What are the risks of welding repairs on older Harley-Davidson pan heads?

Older Harley-Davidson pan heads, manufactured between 1948 and 1965, are made from weaker sand-cast aluminum. This material makes them more susceptible to cracking during welding repairs compared to heads made from more robust alloys.

More Gunsmithing & DIY Videos You Might Like

More from Dragonman's

View all →