How to Repair a Car's Cracked Cylinder Head

Written by ehow cars editor
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Up until recently most engine blocks or cylinder heads with cracks were cast aside as not salvageable; it wasn't worth the time or expense to fix them. With new welding technologies available to engine rebuilders, the possibilities are limitless. An experienced welder can even rebuild his own car's engine at home.

Skill level:

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Things you need

  • Hand grinder
  • Oven
  • Flame sprayer
  • Nickel weld
  • Safety goggles
  • Welder's gloves and apron
  • Insulating blanket
  • Oxyacetylene torch
  • Cast iron filler
  • Borax flux

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    Flame Spray Weld the Crack

  1. 1

    Identify the cracks. Cylinders with a crack might have less carbon buildup than those that are fully-functional. Clean all of the heads thoroughly and look for cracks throughout the entire engine block.

  2. 2

    Grind out the crack with a hand grinder. You're essentially rebuilding the wall of the head, so you need to make sure the area that you're welding is clean and not going to change the shape of the head.

  3. 3

    Preheat the head to about 700 degrees, and weld the repair area with the nickel sprayer. Make sure the head is hot enough that the weld sticks instead of ricocheting off.

  4. 4

    Post-heat the head after the weld is complete to relieve stress in the repaired area. Allow the head to cool down slowly with it wrapped in an insulating blanket. Keep the cool down 50 to 100 degrees per hour.

    Furnace Weld the Cylinder Head

  1. 1

    Follow Steps 1 and 2 in Section 1. Then proceed to Step 2 in Section 2.

  2. 2

    Preheat the head to 1,000 to 1,500 degrees in an oven and allow the temperature to stabilize. This takes roughly 1 hour.

  3. 3

    Use an oxyacetylene torch with slightly more acetylene than oxygen running through the line to melt the iron filler rod and apply it to the area for repair. Add a borax flux a little at a time as you weld to get the impurities to rise to the top of the repair and remove them.

  4. 4

    Wrap the head in an insulating blanket and allow it to cool down 50 to 100 degrees per hour. Don't allow it to cool more than 200 degrees per hour.

Tips and warnings

  • Consider using pins for your weld rather than iron filler. Ask an expert for his advice on your repair.
  • Learning to weld well for this application requires months of practice. Don't be surprised if the first several times you attempt a repair there are problems with porosity or recracking.
  • Because the process requires an immense amount of heat and experience, please consider finding a local shop that specializes in engine rebuilding for your repair work.
  • This process gets very hot. Be sure to take all available safety precautions. Consider paying a shop that specializes in engine rebuilding to do this for you.
  • Welders all seem to agree that it takes about a year of repairing cylinder heads to be able to do this work effectively. Consider finding a shop with experience to do this for your car rather than attempting it yourself.

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