24 replies to this topic

[morley]

Hi guys, I'm looking to lighten and strengthen my front subframe. I plan on doing this by seam welding around the towers and adding guesses to the tie rod mounts, is there any other ways of adding some more rigidity to compensate for the lightening?

I also want to drill some holes in the front subframe and swage them too, I've seen a lot of people drill holes in the front subframe but not swage them? Is it possible to swage holes in the front subframe? Does anyone know the thickness of metal that the subframe is made from?

Thanks

[sonikk4]

Seam weld along all of the joins. I normally do an inch miss an inch or do them two inches in length etc. The metal is thick on the front well over 1.2 mm probably 1.5 mm so might be a pig to swage.

[Cooperman]

The front sub-frame is well over-engineered as it was a new concept in 1959. So long as the extra welding is carried out to a good standard then you could easily cut holes in the flat sides, maybe a pattern of 1.5" diameter holes. You could also cut lightening holes across the front of the frame about 1" in diameter at a pitch of 2.5".

 

The metal is a bit thick for swaging, but just cutting holes will be fine.

 

However, whilst this is a good modification for competition where every ounce counts, it is not advisable for a road car and the insurance company might not like it, even though it is safe. As it is a modification to the structure would it then need an IVA inspection?

[benjy_18]

Check my thread and also look at madmk1's

Plenty of room for weight loss in the front stubby, I lost around 2-3kg iirc

[Cooperman]

That sounds like a good result. But if you just scrape the sound deadening material off the floor you save between 15 and 18 kg. (I weighed it last time I did it on a 1990 Cooper 1275).

Still, it's worth doing once all the other things have been done to save weight, like plastic windows, carpet under-felt removal, rear seat removal, cutting away the inside door skin on the cars with wind-up windows, GRP bonnet & boot (where the regulations allow), removal of servo, plus anything else you can think of. 

[Carlos W]

That sounds like a good result. But if you just scrape the sound deadening material off the floor you save between 15 and 18 kg. (I weighed it last time I did it on a 1990 Cooper 1275).

Still, it's worth doing once all the other things have been done to save weight, like plastic windows, carpet under-felt removal, rear seat removal, cutting away the inside door skin on the cars with wind-up windows, GRP bonnet & boot (where the regulations allow), removal of servo, plus anything else you can think of. 

 

Go on a diet! 

 

I reckon I need to lose 10 Kg! 

[benjy_18]

Agreed, but when you see mine and Simons car (admittedly more Simons than mine) you'll see they're isn't much left to loose weight from. But I agree, if you haven't looked elsewhere on the car first I wouldn't attack the stubby just yet

[morley]

Thanks for the advice guys, the swaggers I have will swage steel up to 1.5mm so I'll have a measure of the steel and see what happens.

In only looking to lose a little weight, and I'm avoiding fiberglass and carbon, i know there's not a massive amount to be lost from the subframe but every little helps as they say, grams make kilograms

[mini93]

Thanks for the advice guys, the swaggers I have will swage steel up to 1.5mm so I'll have a measure of the steel and see what happens.

In only looking to lose a little weight, and I'm avoiding fiberglass and carbon, i know there's not a massive amount to be lost from the subframe but every little helps as they say, grams make kilograms

 

Beware, it may be upto 1.5mm of softer material, like Aluminium. but if it does say steel is it a hand swager? like the type you wind a bolt into a male and female side to form the shape? While the tool may cope, you might have to be Bruce Banner to actually wind it in.

[morley]

Yes it the type which you describe, upto 1.5mm in steel and 2mm in aluminum.... there's only one way to find out if it'll work!!

Thanks for the advice guys, the swaggers I have will swage steel up to 1.5mm so I'll have a measure of the steel and see what happens.
In only looking to lose a little weight, and I'm avoiding fiberglass and carbon, i know there's not a massive amount to be lost from the subframe but every little helps as they say, grams make kilograms

 
Beware, it may be upto 1.5mm of softer material, like Aluminium. but if it does say steel is it a hand swager? like the type you wind a bolt into a male and female side to form the shape? While the tool may cope, you might have to be Bruce Banner to actually wind it in.

[mini93]

Post pics when you have done it, I think swaged holes look much nicer than plain cut holes and dismissed the idea myself due to material thickness, without trying it

[morley]

Still working on this, haven't made a start on the swagging but I will report back!

What thickness metal shall I use for strengthening the tie rod mounts?
Thanks

[Cooperman]

I use 4 mm steel triangles for reinforcing the tie-bar mounts and they work fine even for forest rallying.

 

Are you racing or hill-climbing yours?

[tiger99]

There is a potential problem when drilling or swaging holes, because roughness in a drilled hole is a stress raiser and can easily give rise to fatigue cracking, and ultimately complete failure, on anything subject to cyclical stresses, like a subframe. However, the risk of problems depends greatly on exactly where the holes are, and how big they are, so many people with modest aspirations towards weight saving and a good eye for areas of maximum stress, may never have problems. The fact that the subframe is mild steel, rather than high tensile, helps too. But it pays to play safe, so always polish drilled holes with something like a mini flap wheel, or at least abrasive paper. Round off the edges if possible, which also helps to keep a good thickness of paint, which becomes very thin on a sharp edge. In this case, making it look nice is very beneficial, and doesn't add any more weight. If you drill them with something like a Bradrad step drill, the deburring radius on the tool (as long as you don't go to the very largest diameter) will round off the edges, if you do it from both sides, then a quick polish round the inside with abrasive and the job is done.

 

Swaged holes are rather more complex. It is vital to avoid leaving tension in the edge, it really needs to be left in a state of compression, and you probably need a two-stage process to achieve that. But swaging can be really good, if well done. A crude way of putting the edge in compression is to put a large flat dolly against the flat side, and hammer the edge as if you are trying to thicken the metal at the edge. A better way involves a second pass with a different back half of the die, which simply presses hard on the edge, keeping the inner part of the die in the hole. A simple spacer ring added inside the swaging die might do the trick. The harder the presure, the better. Or, use a length of tube that buts up against the edge, guided on the inner half of the swaging tool, or a smaller piece of tube that fits the hole, and give it a couple of good hard whacks with a large "calibrated persuader". If the edge is just showing signs of spreading, it is ideal.

 

For plain holes, a technique widely used involves a hydraulic machine somewhat like a giant pop rivetter (a screw-operated device is probably possible). A thin-walled disposable stainless steel sleeve is placed in the hole, and the machine pulls a very hard tapered mandrel through it, which applies a lot of compression to the inside of the hole. This may seem counter-intuitive, because it would seem to be stretching the hole, but it really does work. However, it is only of use in somewhat thicker metal than a Mini subframe, and not swaged, but it may provide some useful ideas.

 

As has been suggested already, your insurance company MUST be informed, or they have a perfect way to avoid paying out on any claim, whether related to the subframe or not. Never give your insurance company the slightest excuse....

 

However, I am convinced that you will probably not need an IVA, because in the apparently infinitesimal wisdom of VOSA, that only applies if you modify the monocoque (flip front for instance, a thoroughly bad idea anyway for structural and safety reasons), or the seperate chassis in a car that has one. They seem to have forgotten about subframes! But, you should never rely on legal advice on any internet forum, for that you really must consult your own lawyer, so my advice is only to play safe, inform everyone that matters, i.e. insurers, and be prepared to revert to a standard subframe if someone such as the MOT tester raises an objection.

[Cooperman]

It tends to come down to what this preparation is for. If it is for racing, make sure the regulations for the events allow it. Some classes require nu body or structural lightening, whilst other formulae allow it.

Fort hill-climbing, you will probably not be allowed in the standard road car class, but then you will be doing other weight-saving so will be well-modified.

For a purely road car it is not worth considering as you won't notice any difference except, perhaps, for increased insurance and there is no point in doing so.