Mar 21, 2017

DIY Skills: How to Loosen a Stuck Bolt With A Blowtorch

We've all come across the stubborn bolt. You know the one. That bolt that needs come off, like, now, but for no visible reason, the nut won't turn. Turns out, there's a simple trick: add a bit heat and get it turning quick. Here's how I make it happen. 

This year, ManMade is part of Bernzomatic's Torch Bearers program. We're sharing some our favortie creative projects and clever ways to use a blowtorch around the house. So, far we've shared we like lighting our grill with a blow torch, walked you through the basics of simple, safe pipe soldering, and built a simple DIY copper pourover coffee stand

Why does this happen?

The problem with a rusted bolt is that the spaces between the threads get clogged with minerals and oxidized metal. Trying to turn the nut around these stuck joints can result in stripping, which transforms a simple task into a real pain in the ... bolt.

That's where a bit of heat comes in handy. Metal expands slightly when heated, so warming up the nut a bit makes it ever-so-slightly larger, loosening the hold enough that it will be able to break free. It's important to keep in mind what you're heating here, make sure it's only the nut, if possible – or the female threads, and not the bolt's male threads. 

Here are the steps:

Look around. We all get tunnel vision on these types of things, so it's easy to overlook things like paint or wires that might get ruined if they get heated up. Use a bit of heat shield or sheet metal if you need to protect something.

Prep the bolt. Use a wire brush to clean off the nut, and add some lubricant to help the process. A few squirts should do it; put it on and let it sit for about 15 minutes. Also, work in a well ventilated area or set up a fan to help flush out any gas from the heating process.

Think safe. You might be under a vehicle or in a tight spot, so always wear gloves, eyewear, and protective (non-flammable) clothing for your arms and neck if necessary.

Heat it up. Light up the torch and heat the bolt slowly, without getting the threads too warm in the process. It's not important to get them red-hot, just consistently warm around the outside. At this point, tap the bolt a few times with a hammer to help break it loose. 


Unscrew and move along. For some extremely stuck bolts, it may take a few heat and tapping rounds to fully break it loose, but I've never had this method fail me.


So, there's my trick to tackling stuck bolts in the shop. Do you have any shop tricks we should know about? Let us know.


This blog post was sponsored by Bernzomatic. Thanks for supporting the brands that support ManMade. 


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Paul M on Sep 07, 2020:

a nut can't be stuck on if it's now a dribble of molten metal :-)

Anonymous on Mar 26, 2017:

It also helps to remember that the hottest part of the flame is at the tip of the dark blue

shad van on Mar 24, 2017:

this should never be done to hardened bolts like grade 5 or higher. the heat anneals the metal weakening the bolt. and can cause a catastrophic failure. if you have to use this method on a grade 5 and higher bolt, always replace the bolt with a new on when finished. before trying this method, try a 50/50 mix of automatic transmission fluid and acetone. it works better than any penetration oil I have ever used.

Colin Usher on Mar 23, 2017:

you have to heat the nut to red hot and then cool it by sprayying it with CRC and then try to turn the nut ,it may catch fire but spray again you see it smoke then try to turn the nut half a turn spray more CRC and retighten and release the nut. it may need the proceedure repeated

Wink Knudge on Mar 22, 2017:

The adjustable wrench should be flipped around when applying heavy torque also, if that's what has to be used.

Larry D Dobbins on Mar 22, 2017:

When I saw the picture of the adjustable wrench (Crescent Wrench) on the hot bolt I cringed. An adjustable wrench should be your last choice for turning a really tight bolt. This is because the jaws tend to open a bit when a lot of torque is applied to a nut which increases the chances of rounding the corners of the nut. When the nut is hot this risk is attenuated. If there is adequate room to swing the wrench 60 degrees, a six-sided closed end box wrench is the best, Alternatively, use a six-sided socket. Both will fit the nut tightly on all six sides. Otherwise, use a twelve-sided box end wrench or socket. Even an open end wrench is better than an adjustable wrench!