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This is not a question about an impact hammer.

Does it help to hit a bolt with a regular steel hammer, before even attempting to remove it?

I saw this done in the following video:

https://youtu.be/-DSuc2a_Y_M?t=1946

(should start at 32:26)

I'm aware of using heat and penetrating oil as well-known tricks that should help. My question is, is there any merit to this particular technique, the hammer?

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    I'm not sure there is any definitive answer to this. I suppose there are some scenarios where it might help and others where it will do no good. I really can't think of much that might go wrong as long as you don't overdo it and damage the threads or breaks something. – jwh20 Apr 5 '20 at 3:48
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    The theory is the vibration caused by the hammer blow helps “break” the connection between the threads. – Solar Mike Apr 5 '20 at 5:46
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    help to release the bolt or help to relieve your frustrations ? – Alaska Man Apr 5 '20 at 17:41
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Yep, do it all the time before breaking out the hot wrench, use a punch the diameter of the bolt head if you have one.

Never had an issue with aluminum threads either, don't get carried away with the hammer blows on aluminum and you will be safe.

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In my experience hitting a stuck bolt with a hammer can sometimes help free it, but it depends on whether it is the bolt head or the threads that are seized. If the threads are seized it doesn't seem to help much - but it usually doesn't hurt to try and you never know, if the bolt head is frozen on then hammering it can often work. I've found that the best way to do it is to hammer at a 90 degree angle to the bolt head, and work your way around it.

If the head and the threads are frozen on breaking the head free can allow penetrating fluid in and give you a better chance of breaking the threads. Worst case is hammering doesn't work but makes you feel better ;)

So give it a shot as long as the component isn't fragile.

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This is not something I would be doing or suggest to other to do. There are two major reasons why:

  1. If the bolts go into an aluminum thread, the shock of the hammer blow could very well bust the threads loose, causing you to pull the threads out with the bolt, stipping the hole. Even with cast iron you run this risk, just not as big. If, for some reason, the bolt just happens to be loose in the first place and you hit it with a hammer, that increases the odds of this happening. The minute amount of space provided between the bolt and the threads allows movement, which improves the odds.
  2. If you just try to remove the bolts, I would bet they would come out easily in the first place without having to beat on them. In the YouTube video case, they are only torqued to ~7.3 lb-ft ... that's not a lot of torque (in fact, hardly any torque at all).

This wouldn't work at all for a bolt/nut combination at all.

Would I never use this? I can't say that. However, it would be a last ditch effort to try and free a bolt. For me using an impact gun for removing fasteners would be far more common. That's just me, though.

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  • Just one question: where do you think the idea for a hammer gun ie percussive blows came from? – Solar Mike Apr 5 '20 at 14:50
  • @SolarMike - While it might have, an impact gun's blows promote the twisting force, not a dead blow force a hammer would when struck directly on the bolt head. Much safer for the threads, wouldn't you say? – Pᴀᴜʟsᴛᴇʀ2♦ Apr 5 '20 at 17:00
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Hitting a bolt with a hammer works great. I use it all the time with great success. I can think of only once when it did not work and I had to bring out the heat. I have never compromised the bolt or threads using this method. Although sometimes a bolt is in a tight spot and does not lend itself to using this method. Go for it and good luck!

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