When it comes to major engine repair, broken bolts seem to be a way of life for the mechanic. Bolts can seize inside aluminum engine blocks, due to constant expansion and contraction, rust, debris or even age. Removing broken bolts from aluminum blocks presents several challenges, depending upon the aluminum surface and the amount of bolt material left. A competent DIY repair person can find the correct technique for his bolt removal by using some basic tools and following some specialized techniques.
Instructions
- 1
Clean the surface of the aluminum block with carburetor cleaner and a wire brush. Wipe away all residue with a rag. If the broken bolt protrudes up past the block surface, squirt a liberal amount of penetrating oil into the bolt edges and let it sit for 4 hours or more. For best results, apply penetrating oil to the bolt twice a day for five to seven seven days to ensure complete thread saturation.
2Clamp the jaws of a pair of vise grips around the top of the protruding bolt and turn it counterclockwise. Alternately turn it counterclockwise, then clockwise, to release the threads. When it breaks loose and unscrews, reset the jaws on the vise grips and unscrew the bolt all the way out.
3Apply a flame from a propane torch to the bolt seat on the aluminum head for two to three minutes, until it glows pink. Let it cool naturally, then heat it again for the same duration. This works well if the bolt refuses to move with vise grips. Heat and cool several times, then apply the vise grips and extract it.
4Use a drill and grinder bit to grind off the top of the broken bolt flush with the aluminum block, if it does not have enough material for the vise grip to attach to. Apply generous amounts of penetrating oil and let it soak for four hours or more. Use a hammer and center punch to drive a pilot hole mark in the exact center of the bolt top. Drill a first hole into the bolt, using a small 1/8 inch drill bit. Drill a second hole with a slightly larger drill bit. Then use a bit that corresponds with the exact diameter of the bolt to drill a final hole.
5Match a cutting tap with the exact diameter of the bolt hole, one that has the same thread pitch. Twist the tap handle clockwise to cut into and clean away the old bolt threads. Add penetrating oil to help clean out the hole. Turn the cutting tap in all the way, then back it out. Do this several times. This will expose the old threads, but they will be clean and ready for the installation of a new bolt.
6Obtain a helicoil kit, if you have successfully removed the old bolt but the block threads are stripped. Attach a helicoil spring thread, which has the correct length, size and pitch of the old bolt, to the helicoil insertion handle. Twist the handle (clockwise) and drive the new spring thread down inside the bolt hole until it bottoms out. Turn the helicoil handle counterclockwise to remove the tool. You can now insert a new block bolt into the newly manufactured bolt threads.
