Using Heat for Automotive Work

[mtbtim]

Hey Dudes, I have a question for you guys that utilize heat when removing various components from the vehicles you're working on. Especially you dudes that live in the Salt Belts of the country and are faced with lots of rust. A dude that wrenches in Mother Russia on Toyotas and who I have to use a translator program to understand what the hell he's saying, says using heat can weaken the metal.

I've used heat primarily to facilitate the removal of bushings from control arms both front and rear and now this Russian dude has me thinking. Am I compromising the strength of the steel by using heat? Is some heat ok? How much is ok?

What's your guys input on the use of heat?

 

[T4R2014]

Maybe he's right, but then tell me what he does instead of heat.

 

[mtbtim]

Maybe he's right, but then tell me what he does instead of heat.

He burns out the center part of the bushing which leaves just the bushing sleeve. The he takes a screwdriver and pounds it in between the control arm and bushing sleeve, which deforms the bushing sleeve inward and then he keeps pounding until the bushing comes out. It looks like it worked pretty good. Since he concentrated the heat on the bushing and not the control arm, the control arm never got really hot.

 

[thegipper]

Depends on how much heat, what you are using it on (metal type) and for how long.

In general, it's not going to hurt a thing. Especially if we are just talking about propane or MAPP gas.

If you're using an oxy acetylene torch and are nuking a component until it's red hot, I guess it could potentially compromise the metal.

I've had to "nuke" so many parts over the years but I've never seen any failures because of heating it up.

I'm not a metalurgist nor do I pretend to be though....



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[gamefreakgc]

From what I understand, it's not the heat that damages the component (unless you are heating it red hot so that the shape could deform!) but rather the cycle of heating and cooling. I suppose if you were exposing a part to extreme heat on a regular basis it would develop small stress fractures and eventually could fail. But the occasional blow torch to get a stubborn bushing or rusted nut off I highly doubt will cause failure. Otherwise we'd be hearing horror stories of suspension parts, steering racks, etc. falling off.

 

[mtbtim]

From what I understand, it's not the heat that damages the component (unless you are heating it red hot so that the shape could deform!) but rather the cycle of heating and cooling. I suppose if you were exposing a part to extreme heat on a regular basis it would develop small stress fractures and eventually could fail. But the occasional blow torch to get a stubborn bushing or rusted nut off I highly doubt will cause failure. Otherwise we'd be hearing horror stories of suspension parts, steering racks, etc. falling off.

You said exactly what I was thinking too. I know the application of heat to remove stubborn parts is pretty common and if it ended up causing failures we'd definitely hear about it.

 

[kolelt]

In my of field. ( iron worker )If you use a torch let’s say to widen a hole. You actually just hardened the steel than it was before. Thus making it more brittle. In some cases, that could be bad, because originally it was not designed to be that hard. But how often do we get it HOT or torch shit of ??

 

[mtbtim]

In my of field. ( iron worker )If you use a torch let’s say to widen a hole. You actually just hardened the steel than it was before. Thus making it more brittle. In some cases, that could be bad, because originally it was not designed to be that hard. But how often do we get it HOT or torch shit of ??

When I've removed control arm bushings, I have gotten the arm hot enough that I start to smell burning rubber. I've read on a website that rubber will melt at 350 degrees. Since I'm smelling the burning rubber, I'm assuming I've heated the metal somewhere close to that 350 degrees. I've never seen the rubber of the bushings deformed or melt out unless I accidentally started the rubber on fire from direct flame contact from the torch so I know heat transferring from the control arm to the bushing was under 350 degrees.

Here's the link to that website:How-To Burn out Suspension Bushings: The Right Way - Suspension.com

 

[JZiggy]

When I've removed control arm bushings, I have gotten the arm hot enough that I start to smell burning rubber. I've read on a website that rubber will melt at 350 degrees. Since I'm smelling the burning rubber, I'm assuming I've heated the metal somewhere close to that 350 degrees. I've never seen the rubber of the bushings deformed or melt out unless I accidentally started the rubber on fire from direct flame contact from the torch so I know heat transferring from the control arm to the bushing was under 350 degrees.

Here's the link to that website:How-To Burn out Suspension Bushings: The Right Way - Suspension.com

Just thought of something... automotive bushing rubber is almost certainly vulcanized (ie crosslinked) like tire rubber. This makes the rubber much stronger and more durable. But after its vulcanized it can't melt anymore -- all it can do is burn, hence the chemical reactions you're seeing in the video clips on that page. This is probably somewhat hotter than 350F since we're breaking chemical bonds and not just softening a thermoplastic.

 

[phattyduck]

I think it would generally be a bad idea to reuse a fastener that needed heat to remove (other than heating to soften red loctite or similar).

As for the surrounding metal - it is put in compression by the fastener, generally and shouldn't be much of problem if it locally changes properties a bit.

-Charlie

 

[spartacus]

Cooling the metal after heating is really important. During the annealing process metals like iron or steel are heated to a level that they can be shaped but are allowed to cool real slow so that they are not brittle. So as long as you dont put a hot control arm in cold water it should be fine. If this russian guy is in siberia he might be right.

 

[Wedgy]

Unless you quench(cool it rapidly in liquid) the heated metal you won't change its properties of hardness, at the temperatures we are using. When you quench you are heat treating which can make the metal brittle, but again we are talking red white hot glowing hot, like in a forge.

 

[mtbtim]

Thanks for all the responses. Sounds like to me it's fine to use some heat to remove parts as long as we aren't getting parts red hot and then rapidly cooling them (quenching) which will make the metal more brittle.

 

[kolelt]

Like others have said. I don’t think we get the metal that hot to the point where we are hardening it. Maybe , we harden the metal very very little. But applying heat. Getting it hot, burning something. Will harden the metal and make it more brittle than it was designed for.

We use this tool called “reamer”. To fix a bad bolt hole. So we could put the bolt through it. I’ve noticed that if you ream the hole before burning it. It does the job. Now if you torch the hole, and try to clean it up with a reamer. The reamer has a really hard time and a lot of times it can break. Because the steel is now a lot harder than the reamer is made of. Because of the torch. Basically when you ream before torching. It likes eats the metal. But when you torch and ream after. It has a very hard time cutting through the metal. In school they tell us, Heat changes the metals property. I just don’t know how hot it has to be

I wouldn’t worry about the LCA. I used heat on mine to, but no where near close to red hot.

 

[rallypoint_1]

Sounds like Tim should make a vid on this!!!

 

[Scramble]

Sounds like Tim should make a vid on this!!!

On what? Kolelts hole reaming? :hatsoff:

You said exactly what I was thinking too. I know the application of heat to remove stubborn parts is pretty common and if it ended up causing failures we'd definitely hear about it.

Most of the time we're only trying to expand a nut to get it off a bolt or stud with mapp or propane. If we use oxy/acyl most likely we're cutting that part off & not re-using it.

 

[rallypoint_1]

On what? Kolelts hole reaming? :

Yikes!!

 

[kolelt]

On what? Kolelts hole reaming? :hatsoff:



Most of the time we're only trying to expand a nut to get it off a bolt or stud with mapp or propane. If we use oxy/acyl most likely we're cutting that part off & not re-using it.

I’m not reaming any holes on my truck lol. At work. When you have a connection that a bull pin or barrel pin does not fix it. You next choice is a reamer.

 

[LittleCaesar]

Have used oxy/ace for over a decade with no problems to speak of, though I have always heard and used MAP wannabe gas on rusty O2 sensors and not oxy/ace due to the latter being able to contort the bung hole.

A gas ax is one lovely tool to own in one's arsenal though for [MENTION=120071]mtbtim[/MENTION], the MAP kit would probably suffice for all his needs.

 

[sleepydad]

Thanks for all the responses. Sounds like to me it's fine to use some heat to remove parts as long as we aren't getting parts red hot and then rapidly cooling them (quenching) which will make the metal more brittle.

Your not getting it anywhere near hot enough to temper, anneal, normalize, Or harden it. Just think about how much heat goes into the steel when they weld it. The only reason I don’t like to heat things is because it tends to burn the paint off. You might in extreme cases put enough heat into it to case harden a very small part of it.

https://youtu.be/KFdFsfSAuyc

This is a fantastic trick, I have used it a bunch of times. On mufflers, a friend bet me $20 I could not get his 20 year old rusted exhaust bolts off. With this trick they came right off. It’s seriously like magic.