need to bend a steering arm, will MAPP torch suffice?
 

I need to bend (twist, actually) a steering arm on a front 911 strut. Will a MAPP torch provide enough heat to get that cherry red? I'm guessing no.

If not, will a portable oxy acetylene kit work from home depot?

thank you,

Doug

Nossir,...an oxy-acetylene oufit is required to do that job.

Mapp won't do it.

While I encourage the DIY attitude, as the victim of a modified strut that broke at 100+mph, I strongly suggest leaving that mod to the expert that has done dozens. Better yet Hundreds.

If you're doing this to correct bump steer, Why not use one of the kits from Elephant? ELEPHANT RACING Adjustable Bump Steer Kits for Porsche 911/912/930

Just had my passenger side front strut repaired at Johnson's Alignment in Torrance.

It was 1.0 degree off (bent in or too negative) so he removed the spindle, positioned and re-spot welded it, a nice 1.5" spot weld.

Thanks Doc Steve A!

I have a bumpsteer kit made by rebel racing. The steering arm was not reinforced at the time that the spindles were raised. A very minor offtrack excursion twisted the arm just a bit, due to the extra leverage of the bumpsteer kit (the stack of spacers is several inches high).

My plan was to heat to cherry red, return to near zero toe, fine tune with normal toe adjustment procedure (via tie-rods) and add Rebel Racing's water-jet-cut reinforcement plates, which are welded to the strut tube and parallel to the arm itself. I'm very proficient with a MIG. I figured with the reinforcement, it'd be stronger than before.

Bad idea?

***Note, Ed (175K) posted a picture of the reinforcement installed, below. Apparently, Elephant Racing and Rebel Racing offer very similar reinforcements.***

Sounds like a good plan to me. That is what the pros would do.

A bit of more info.... there is a casting line along the sides of these arms. They are straight, as cast. Mine has an obvious twist to the casting line at the point of the bend / twist. I planned to heat there.

Bear in mind, the extra leverage of the bumpsteer kit makes the change in toe by the very small twist of the arm quite pronounced.

thank you all,

Doug

Were they cast or forged? I wonder if there will be any heat treatment effects?

That proceedure has been done many times before with great results, though.

Clint from Rebel Racing had said cast. That's what I had assumed, due to the casting lines on the arms.

Another Pelican was kind enough to PM me to warn me about the effects of cooling on the metal's properties.

Maybe after adding the Rebel Racing reinforcement, I'll add another gusset just to be safe. The Rebel Racing reinforcement is essentially a narrow 1/8" triangular plate with two circles cut out, one from each end. One circle abuts the round strut tube and the other surrounds the threaded shaft attaching the steering arm to the tie rod.

I could add another gusset north to south oriented further tying the arm to the strut tube?

Doug

If you do heat and bend it back to shape, I'd go all the way and really make sure it never happens again. While I like Clint's products I'd be tempted to add one of Chuck's racing bump steer kit too. I have it on my raised hub Bilsteins and it appears to be far more rigid that just a modified steering arm...
<img src=http://elephantracing.com/suspension/bumpsteer/front-coilover-doubleshear600.jpg>

Hi Ed,
Clint's reinforcement is nearly identical to what you have posted.
I think I misled a bit in an above comment. A picture is worth 1k words. Thanks for posting.


Doug

Didn't realize Clint was doing the same thing. good to know.

I like this setup much better than the traditional tie rod end spacers to correct bump steer. There should be zero flex which ought to translate into less steering kickback.

If they were cast, then I would not suspect they were heat treated or cast in a special way to control grain size. With a thin arm like that, the cooling rate should be a good medium fast so I do not think you will have any problems with softening the metal or making its properties different from the un-modified areas.

The Rebel Racing reinforcement should be fine. It is located at the point of maximum leverage and as long as the triangle is wide enough, it should be fine. Clint does great work on those struts. There are also those little vertical gussets and other welding and reinforcement with the raised spindles...

Very scarey -

Just what do we mean by Cherry Red??

Dull Cherry Red 700 to 750 deg C

Cherry Red 750 to 825 deg C

Bright Cherry Red 825 to 875 deg C

It is certainly true that if you heat to Dull Cherry Red the steel will be weakened and will bend quite easily but you will also have a negative effect on the microstructure and could substantaily change its notch sensitivity.

Heating to a Bright Cherry Red is much safer from a metallurgical point of view.

As I am sure you all know steel undergoes a change in crystal structure when heated.

In a medium carbon steel this change starts to take place at 723 degC and the structure should be fully transformed by 860 degC.

If you start to bend at temperatures of say 735 deg C you can damage the microstructure quite significantly and open up very small surface defects.

It is much better to hot work steel when it is fully transformed and most forging and rolling takes place at around 1000 degC. but ususally in a well controlled environment.

If you heat a steel component in a relatively uncontrolled manner then you will cause an uncontrolled change to its microstructure so the results must be a bit uncertain.

I have always worried about bending Bilstein Steering Arms and have seen problems with the Ford Escort arms in particular.

It is common to bend these arms to eliminate bump steer as the rack mounting of a Rally Escort needs to be lowered to stop it bashing the sump. If you don't bend the arms you have massive bump steer.

When we bend these arms we always use a Tempilstick to try to have some control of tempertaure and we always re-heat treat the complete arm after it has been bent just to be sure.

We are just about to bend some Porsche steering arms to see if we can introduce some Ackermann and have made a jig. We plan to take the stub axle completely off the leg, locally heat, bend to position and then re-heat treat. We will then weld it back on with the RSR type strengthening plates.

By coating the part in Berkatekt 12 before heat treatment we will eliminate any oxidation or decarburiastion during heat treatment.

The Berkatekt can easily be removed after by washing in hot water.

I know I tend to worry about these things but heating up critical components without control can be fatal.

Max,

I think they are forged not cast. the lines along the steering arms result from the 'flash' that is produced in the forging die being clipped after forging has taken place but whilst the part is still hot

That is what I thought as well. My Konis look to have a mark from a die rather than casting flash being ground off. The steering arms are quite long, thin, and curved to be cast parts without any other sort of heat treatment to make them more rigid.

I agree with all you said, in the case of forged parts.

I would not heat and bend a forged part because it would modify the crystal structure and stronger, stiffer material properties which that forging/hot working process set up. I would only do it with knowledge of the prior forging method, temperature, and any other heat treatment. And then only with a post bend (or weld) heat treat to bring back the original material properties throughout.

If they were cast, I do not think they would have had a controlled cooling/heat treatment to control grain size and direction and material strength, toughness, and stiffness.Therefore, heating and cooling from a torch should just be raising and lowering the temperature at similar rates to the original casting process, no? :confused:

If you heat a cast steel to above its AC3 temperature it will still transform to austenite and the rate at which it cools will still influence the ferrite/pearlite structure. If you heat it locally there will still be a visible heat affected zone

If you cool it very rapidly and the carbon content is above around 0.4% it may even transfrom to martensite which would be a real problem.

It is unlikely that air cooling will cause this but if someone decided to pour water on it to cool it more quickly it could be fun.

I guess what you are saying is that the properties of a cast part are relatively poor and likely to be variable so any mucking about is unlikely to be a problem, I could agree with this idea but I am not sure that a cast part is good enough.

I just called the Technical Manager at Bilstein UK and he says that these parts are forgings. (At least on the Bilstein Units)

I can't get them to tell me the material specification on the drawing but I would imagine it is a low-ish carbon steel.

These are indeed Bilstein struts. Clint did the original spindle drop modification. I have the triangulated gussets at the spindle mount to the strut tube body, but he did not add the modification shown above by Ed.

Thank you for all of the interest and consideration.

Is there some idiot-proof method for repairing this? Or shall I just send the strut out and have a new arm added?

My thought is the part will see greatly reduced stress, if I add the reinforcement. I could also weld a gussett between the reinforcement shown above and the arm. I've seen that modification on other Porsche steering arms.

Look forward to your input.

Doug

Doug,

I think you can do this if you are just a bit thoughtful.

I would buy a Tempilstick of the correct rating which should only be a few dollars.

850 deg C - 1560 deg F

Warm the area you are going to bend gently and check the temp using the stick which is chalky and melts at the correct temp. These sticks are easy to use.

Don't let it cool too much before bending.

Let it cool naturally and then I would suggest you warm it up again but only to a black heat to give some stress relief.

With the stiffening plates I would think it will be OK.

It is more important not to bend it when it is not quite hot enough.- if that makes sense.

Great advice. How hot will it need to get for stress relief? Same temp again?
thank you very much,

Doug