How to free rusty fasteners with a blow torch

By Carl Heideman
Apr 13, 2024 | Torch, Hot Wrench, Blow Torch | Posted in Shop Work | From the Dec. 2017 issue | Never miss an article

Photography by Carl Heideman

[Editor's Note: This article originally appeared in the December 2017 issue of Grassroots Motorsports.]

Despite the often-shared advice about not buying rusty project cars, sooner or later you’re bound to encounter one. And those rusty cars are filled with rusty, crusty and cruddy fasteners–the kind that can rarely be loosened, even with chemicals. 

There is another option, though: the hot wrench.

We’re not …

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dean1484 GRM+ Memberand MegaDork
11/15/17 4:17 p.m.

A rosebud torch is also very useful. 

RealMiniParker UberDork
11/15/17 4:44 p.m.

Streetwiseguy UltimaDork
11/15/17 4:57 p.m.

I presume there is a paragraph in there somewhere about being very aware of where the rest of the fire is going...CV boots, brake hoses, ball joint boots...I've burned holes in all of these, and more.blush

ssswitch Dork
11/15/17 5:39 p.m.

In reply to Streetwiseguy :

The real lesson is in not immediately putting your hand on the metal surrounding the hot fastener.

Vigo UltimaDork
11/15/17 9:07 p.m.

Regarding the 'only want to heat one of the mating parts' thing, i've actually had decent luck with ice cubes. Heat both parts, hit one with an ice cube (or any non-flammable spray that comes out cool/cold) and soak the heat out of it to shrink it while the other part is still hot. I also recently learned that when you heat a fastener that's inside of a larger/stronger part, the attempted heat expansion actually compresses the part somewhat and when it cools off it's slightly smaller in the constrained area than before you started. 

ChasH New Reader
11/15/17 10:55 p.m.

I watched a co-worker using a blue tip wrench drop the object of his attention into the pocket of his shirt. He was a smoker so there was also a book of matches in there. 

There was much to be learned from that. 

NOHOME UltimaDork
11/16/17 12:20 p.m.

I get by using a plumbers rig, that being acetylene but no oxygen tank. Cant weld with it, but works fine for nuts and bolts.


RevRico GRM+ Memberand UltraDork
11/16/17 12:24 p.m.

I've become a big fan of using a candle with the torch.

Heat the parts up, touch the candle to the threads or end of the nut, wax goes into threads, bolt spins right out.

Kendall_Jones HalfDork
11/16/17 12:38 p.m.
RevRico said:

I've become a big fan of using a candle with the torch.

Heat the parts up, touch the candle to the threads or end of the nut, wax goes into threads, bolt spins right out.

Likewise, but I quench with Kroil.  Spent a long time working on rusty cars in Detroit area, now spoiled in PNW.  I just did a tie rod change on my wifes minivan which was a rust belt car in the past.  Used propane, wrenches, cheater bars (completely unprepared) and half a sunday but got it done.

jimbbski Dork
11/16/17 1:34 p.m.

I have a friend who got his start as a auto mechanic at a Midias Muffler shop.  I saw him remove a rusted, broken flush stud in an exhaust manifold by heating the stud red hot with a cutting torch and then blowing out the stud with the O2. All the threads need was a quick clean up with a tap.  


AS for me while I have the torch, gauges, and hoses I don't have the tanks.  When I can access the nut on  a rusted nut/bolt assembly I try to use my nut splitter.

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