I need to remove a lot of steel bolts from an aluminum engine block, they feel like "welded" in there because the level of rust. Just turning them would crack the part, or break the bolts. I wonder what's the best/fast way to remove them, with minimum parts damage. I know:

  • Use a propane torch to heat the bolt
  • Cut the bolt at almost surface level then
    • Do a cone drill and a cone bolt tip, arc weld the bolt
    • Do a passing-through drill almost the bolt diameter to make it weak, then pass another threader, and then the one the bolt was
  • Use salted water electrolysis to dissolve steel

Then finish unscrew it by any means :)

My experience:

  • Propane torch, very few tries, but see they need a lot of heat
  • Arc welding a bolt on top: a few times, but difficult to control for small bolts
  • Drill to make it weak and thread: needs a lot of work, basically re thread with new bigger sizes on each try...first M10, then M8, then M6.

Electrolysis...I'll put this aside as it is "special" and unorthodox for this, I believe. Once upon a time :) I "had" a long-term hobby making art blades, swords, knives and used it for engraving. Now the hobby time is going to the the darn car :) Anyway, it eats steel "fast", but need prep work. Salted water electrolysis won't eat aluminum.

Any other ideas? I need to extract about 15 old rusted bolts like those:

enter image description here

  • 2
    OK! all studs are out! I used kerosene first to damper where they sit, then a propane torch to heat them but curiously non of the studs needed to be red hot...just a couple of minutes applying heat, then nut and "counter nut" to extract them. Worked nicely. Nov 25, 2016 at 1:47

4 Answers 4


They're not bolts, they're studs. You can use a stud extractor if needed but my usual trick is to put two nuts on, tighten one against the other then turn out the stud with the lower bolt. You can apply heat with a blow torch if they aren't shifting or try some releasing fluid such as PlugGas / PB Blaster (being careful not to use heat and flammable liquids together).

Make sure the part you are trying to get the stud out of is firmly clamped in a vice. Trying to take these out with the part in your arms or under your knee complicates things significantly.


In my experience most penetrating oils (PB Blaster is my personal favorite) work well when dealing with iron oxide (rust). They are not as effective with aluminum oxide. A common scenario when working on bicycles is steel hardware stuck in aluminum frames. What works reasonably well in ammonia. Put straight household ammonia in a spray bottle. Soak both sides of the part if possible. I will go so far as to soak a strip of cloth and wrap it around the base of the stud. Patience is the key. Soak it for several days if possible. If you detect some movement then proceed as @Tim has slowly work the hardware in and out reapplying the solvent frequently


Soak in WD40 or similar release fluid for a few days. Heat up the stud with oxy acetylene, cherry red. When the colour's gone, apply more WD. Use a stud extractor if possible. After turning half a turn, apply more fluid, screw back in and gradually unscrew in this manner. Rather like tapping a hole in reverse. Keep up the treatment until out. It will not always work, so if a stud breaks off, drill and tap, with cobalt bit, and either tap appropriate thread again, or use helicoil. Be careful to be perpendicular to the face.

  • 1
    Exactly what I did. Heat and soak again and again. But be careful: cherry red is about 760°C, while alu melts at 660°C. This could make things worse.
    – sweber
    Nov 24, 2016 at 11:55
  • @sweber - fair comment, although aluminium blocks are great heat sinks, and heat dissipated should keep it below melting point. Certainly wouldn't go hotter, and only torch the stud. The idea is the heat will travel through the stud to the alu, and weaken the rust/alu amalgam.
    – Tim
    Nov 24, 2016 at 11:59
  • 1
    True. It's just: when you write cherry red, people tend to heat the entire thing until it starts to glow and well beyond.
    – sweber
    Nov 24, 2016 at 14:43
  • 2
    WD-40 is not a penetrating oil! Use Kroil or other real penetrating oil. Nov 24, 2016 at 22:19

One method that works on many rust problems and is safer thanmost, is you can apply heat with a oxy acetylene but be careful, just heat for a short time then use a non flameable like bees wax or regular wax, it melts in to the threads but will not burn off like most all sprays, with a stud remover , see if the stud will turn,either forward or backward, if it moves slightly without a slight squeek noise it is twisting off and not moving, just heat again and add more wax and let it set a minute or two and try again, like has been said patience is the key,its not unusual to to have to heat it 3 or 4 times, but it is faster than drilling and tapping for an hour ,or causing a fire. I have tried every spray out there and one works good without heat, like on a plastic mouldings with aluminum fittings and steel lines and that is a commerical spray by BG products.

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