If the bolt is so obscured that vise grips and welding are not feasible, and so stripped that impact doesn't make sense (I am guessing it is too stripped), I usually do the following. If it's very stripped, you might want to skip ahead to step 8.

1. (Look ahead to step four; you'll probably want to take one of your bolts to the auto parts store before starting this process.)

2. Torque down the other bolts in order (follow manual)

3. Add about 5 ft*lb to the bolts nearest to the stripped bolt (this is intended to unload the bolt) and don't plan to re-use the head bolts because they're overstretched now

4. Get the next size up allen key or torx bit that will almost fit into it and hammer it on. I'd recommend doing this with a bit you don't care about, preferably impact rated due to hardness. I'd recommend 1/2" drive for this bit if space allows. If you're wondering what will fit, see this diagram:

   

   That diagram shows the difference between your bolt (left) and a 12 point socket (right). Notably, an allen key or torx bit would fit into this. If your fastener is standard, use a metric (and vise versa) to get a size that's just a little bit off (i.e. a little bit bigger).

5. When you're done swinging the hammer, soak everything in penetrating oil

6. If you're feeling confident after hammering, feel free to try removing it BY HAND now. If you use impact tools with this technique, you will successfully extract the bit from the bolt and continue having a bad day.

   • If you feel it start to strip, stop and apply more penetrating oil and apply some heat.

7. If that strips out, consider trying a different sacrificial tool.

8. If the above doesn't work, clean up the bolt with brake cleaner, get a new sacrifical bit, and JB weld the two together following the above process. Wait at least 8 hours and then take it off by hand. Don't forget to apply liberal penetrating oil (after the JB weld is set) and I would personally apply heat to the bolt only at this point.

9. The bolt will be out. On reassembly, chase the hole gently with a tap and blow it out with an air compressor. If it took your block's threads with it, get a helicoil, install it, and use a lot of oil (maybe even anti-seize) on the coil threads when you re-attach the head if you want to be able to remove it. When you go to try removing the bolt from the helicoil in the future, it will likely take aluminum with it. Helicoils are nightmares in disguise. Seriously consider never removing the head again if it comes to this.

If the bolt is so obscured that vise grips and welding are not feasible, and so stripped that impact doesn't make sense (I am guessing it is too stripped), I usually do the following. If it's very stripped, you might want to skip ahead to step 8.

1. (Look ahead to step four; you'll probably want to take one of your bolts to the auto parts store before starting this process.)

2. Torque down the other bolts in order (follow manual).

3. Add about 5 ft*lb to the bolts nearest to the stripped bolt (this is intended to unload the culprit bolt) and don't plan to re-use the head bolts because they're overstretched now.

4. Get the next size up allen key or torx bit that will almost fit into it and hammer it on. I'd recommend doing this with a bit you don't care about, preferably impact rated due to hardness. I'd recommend 1/2" drive for this bit if space allows. If you're wondering what will fit, see this diagram:

   

   That diagram shows the difference between your bolt (left) and a 12 point socket (right). Notably, an allen key or torx bit would fit into this. If your fastener is standard, use a metric (and vise versa) to get a size that's just a little bit off (i.e. a little bit bigger).

5. When you're done swinging the hammer, soak everything in penetrating oil.

6. If you're feeling confident after hammering, feel free to try removing it BY HAND now. If you use impact tools with this technique, you will successfully extract the bit from the bolt and continue having a bad day.

   • If you feel it start to strip, stop and apply more penetrating oil and apply some heat.

7. If that strips out or you don't feel confident in the seating, consider trying a different sacrificial tool.

8. If the above doesn't work, clean up the bolt with brake cleaner, get a new sacrifical bit, and JB weld the two together following the above process. Wait at least 8 hours and then take it off by hand. Don't forget to apply liberal penetrating oil (after the JB weld is set) and I would personally apply heat to the bolt only at this point.

9. The bolt will be out. On reassembly, chase the hole gently with a tap and blow it out with an air compressor. If it took your block's threads with it, get a helicoil, install it, and use a lot of oil (maybe even anti-seize) on the coil threads when you re-attach the head if you want to be able to remove it. When you go to try removing the bolt from the helicoil in the future, it will likely take aluminum with it. Helicoils are nightmares in disguise. Seriously consider never removing the head again if it comes to this.

If the bolt is so obscured that vise grips and welding are not feasible, and so stripped that impact doesn't make sense (I am guessing it is too stripped), I usually do the following. If it's very stripped, you might want to skip ahead to step 8.

1. (Look ahead to step four; you'll probably want to take one of your bolts to the auto parts store before starting this process.)

2. Torque down the other bolts in order (follow manual)

3. Add about 5 ft*lb to the bolts nearest to the stripped bolt (this is intended to unload the bolt) and don't plan to re-use the head bolts because they're overstretched now

4. Get the next size up allen key or torx bit that will almost fit into it and hammer it on. I'd recommend doing this with a bit you don't care about, preferably impact rated due to hardness. I'd recommend 1/2" drive for this bit if space allows. If you're wondering what will fit, see this diagram:

   

   That diagram shows the difference between your bolt (left) and a 12 point socket (right). Notably, an allen key or torx bit would fit into this. If your fastener is standard, use a metric (and vise versa) to get a size that's just a little bit off (i.e. a little bit bigger).

5. When you're done swinging the hammer, soak everything in penetrating oil

6. If you're feeling confident after hammering, feel free to try removing it BY HAND now. If you use impact tools with this technique, you will successfully extract the bit from the bolt and continue having a bad day.

   • If you feel it start to strip, stop and apply more penetrating oil and apply some heat.

7. If that strips out, consider trying a different sacrificial tool.

8. If the above doesn't work, clean up the bolt with brake cleaner, get a new sacrifical bit, and JB weld the two together following the above process. Wait at least 8 hours and then take it off by hand. Don't forget to apply liberal penetrating oil (after the JB weld is set) and I would personally apply heat to the bolt only at this point.

9. The bolt will be out. If it took your block's threads with it, get a helicoil and use a lot of oil (maybe even anti-seize) on the threads when you re-attach the head. When you go to try removing the bolt from the helicoil in the future, it will likely take aluminum with it. Helicoils are nightmares in disguise. Seriously consider never removing the head again if it comes to this.

If the bolt is so obscured that vise grips and welding are not feasible, and so stripped that impact doesn't make sense (I am guessing it is too stripped), I usually do the following. If it's very stripped, you might want to skip ahead to step 8.

1. (Look ahead to step four; you'll probably want to take one of your bolts to the auto parts store before starting this process.)

2. Torque down the other bolts in order (follow manual)

3. Add about 5 ft*lb to the bolts nearest to the stripped bolt (this is intended to unload the bolt) and don't plan to re-use the head bolts because they're overstretched now

4. Get the next size up allen key or torx bit that will almost fit into it and hammer it on. I'd recommend doing this with a bit you don't care about, preferably impact rated due to hardness. I'd recommend 1/2" drive for this bit if space allows. If you're wondering what will fit, see this diagram:

   

   That diagram shows the difference between your bolt (left) and a 12 point socket (right). Notably, an allen key or torx bit would fit into this. If your fastener is standard, use a metric (and vise versa) to get a size that's just a little bit off (i.e. a little bit bigger).

5. When you're done swinging the hammer, soak everything in penetrating oil

6. If you're feeling confident after hammering, feel free to try removing it BY HAND now. If you use impact tools with this technique, you will successfully extract the bit from the bolt and continue having a bad day.

   • If you feel it start to strip, stop and apply more penetrating oil and apply some heat.

7. If that strips out, consider trying a different sacrificial tool.

8. If the above doesn't work, clean up the bolt with brake cleaner, get a new sacrifical bit, and JB weld the two together following the above process. Wait at least 8 hours and then take it off by hand. Don't forget to apply liberal penetrating oil (after the JB weld is set) and I would personally apply heat to the bolt only at this point.

9. The bolt will be out. On reassembly, chase the hole gently with a tap and blow it out with an air compressor. If it took your block's threads with it, get a helicoil, install it, and use a lot of oil (maybe even anti-seize) on the coil threads when you re-attach the head if you want to be able to remove it. When you go to try removing the bolt from the helicoil in the future, it will likely take aluminum with it. Helicoils are nightmares in disguise. Seriously consider never removing the head again if it comes to this.