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We started with a small-block Chevy intake manifold that suffered from a broken 3/8-inch bolt in one of the thermostat holes. After several attempts to remove it with Vise-Grips, it was time to drill. |
First we ground the top of the bolt flat, then used a punch to create a centered pilot point. Next, we drilled a small pilot hole through the bolt. Finally, we used the recommended 2-5/64-inch bit to completely drill out the rest of the 3/8-inch bolt. |
We ran the tap through the hole (with spray lubricant applied) several times to make sure we had clean threads. A bolt is only as strong as the material surrounding it. |
To install an insert, thread it over the end of the installation tool with the tang at the bottom. Installing a fine-thread insert can be difficult. Perma-Coils kits include a handy prewinder tool to ease fine-thread installation. |
Once you install the insert, be sure to break off the tang at the bottom of the threads so it wont interfere with the bolt. A standard punch will work just fine, but if you install a lot of inserts, the black tang-removal tool is a nice luxury. |
If you turn enough wrenches on old cars, chances are youll break a bolt or two. Breaking a bolt is a rite of passage in the automotive world, and its something every automotive enthusiast eventually has to face. You have tested the strength of metal and pushed it beyond its limits.
Thread repair isnt as difficult as you may think. Installing a thread insert can be done in a short time and will increase the strength of the threads. We recently visited Thread Kits in Torrance, California, and went through the proper procedure for repairing a damaged bolt hole. Thread Kits offers the Perma-Coil line of helical coil-thread inserts and plugs. We will show you how to remove a stubborn bolt and install an insert in a few easy steps.