Page last updated July 17, 2008



Bolt Hole Rethreading / Tapping


You can also braze a bad drill using cheap brazing rods. The photo to the left is another successfull braze used to fill the sides which were too wide and only about 1/4 inch deep. I placed acid flux on area, inserted bolt, heated area and then applied alloy. The first try with tin flux did not fair so well. The piece was loose after I remove bolt, so I started all over and applied acid flux to the area and used SteelAlloy. SteelAlloy is easier to work with and seems to have a lower melting working temperature than the 700-800 degrees with standard rods.

After finishing all other repairs, I applied a small amount of gasket sealant around the area, as well as the rest of the cover, and it did not leak. Above repair, if done carefully and correctly will work.

When creating brazed repair, depending on the type of brazing rod you obtain, you may or may not need to apply flux. The flux allows various thing to occurr. When the metal is heated oxides form rapidly. The flux helps with preventing oxidation of the metals by shielding them from the air, it helps the brazing alloy to flow allowing complete fill and thus allowing the metals to bind together better. If you have self fluxxing rods, then you should still apply the fluxxing step, and I would not advise getting self fluxxing rods. It takes time to heat the metals unless you utilize induction heating process. If you use that, you certainly don't need to read this article. The time it takes to heat the materials will certainly produce oxides on the parent metal so use fllux no matter what, even coat the rod. It should all evaporate in the end.


You should practice with the brazing rods on some metals lying around. The metal needs to be heated: not the rods. The metal when properly heated should melt the rods, not your torch. It takes a bit of practice, but when you have it, you can go on to the block.

My experience with broken headbolts has been 50/50. I can undoubtebly increase my ratio by utilizing a drill press 100% of the time and it requires a lot of time. It is nice to know that the powerhead still has a chance. If the above alloy fails me, I will have to purchase a different alloy with different properties.

If you mess up a bolt like the one at the top of this page, It is probably best to drill out the remaining parts of the bolts if it went bad. Your best bet is a dremmle kit with some mini grinders and some rotozip carbide tip steel cutters. It is a slow process.

Once you have all the remaining portions of the steel bolt extracted, you can braze a new bolt in place (see below) or tap some new thread.

Once the brazing metal dries, unscrew the bolt and file down. Usually, the brazing metal is non-ferrous so a magnet will not be able to pick up the shaving / slivers of left over metal, so cover up all surrounding area and blow with a compressor to remove all debry from filing.

If done correctly, the brazed metal should hold. Remember that a gasket can easily be overtorqued and as a result, you'll end up with a blown head gasket; keeping that in mind, the brazed area should not be over stressed; a gasket only needs a litle past hand tight to perform its function and can easily be crushed and blown from overtorqueing.

If the area is past recovery, you can inspect the area and if capable, you can drill deeper into the powerhead and develop some threads using the deeper hole. You will have to find a headbolt that much longer. It only needs to catch a little, or enough to pull the exhaust cover and hold in place. Be careful, if you go to deep you might end drilling into other portions of the head such as the cylilnder inspect carefully. Also, headbolt threads usually are encased where the metal tapers in as you go further. You will have less metal as you go deeper into the threading. You may or may not be a ble to drill deeper. I will go over this particular repair in detail if my first method (ABOVE) fails me......


Heat up the area and test the rod to see if melts if not, then heat up some more; some metals require a few minutes to heat up to the proper temperature. Monitor the metal you are heating so that you don't melt it. If you have access to more than one torch, by all means utilize them by clamping them down and positioning them so they heat up the parent material. The flux will start to sizzle and evaporate as the parent material heats up.

When you can touch the metal with the rod and it liquifies, you can start moving the rod around trying to get it into the nooks and crannies that exist moving slowly up until the hole is filled. You should continue to heat the head pressing firmly down onto melted new metal to ensure it fills the hole completly if possible. If it was done correctly, the alloy should flow into area by capillary action. If oxides are present, the flow will be minimal and of course, the strength of the bond will be weaker than without oxides.

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