broken header - part 2

The header on the Mini broke wide open last Friday during HPDE at the track.


I did a bit of research about MIG welding with stainless steel, and to my surprise you can. One good articles I found is this by Lincoln Electric, the maker of my MIG welder. However, they recommend using a different mix of gas as well as getting the welding wire for stainless steel. If I were to go to the length of getting this I might as well pick up a cheap TIG welder. Being someone that do just about everything myself, my house is choke full of tools and equipment and I have to be very careful with any new tools that I add.

If I really want to embrace risk taking and not care too much about some compromise in the corrosion resistance of the header, I can always try to weld it back together with my 75% argon/25% CO2 mix, and mild steel wire.

I decided not to rush it. I took the weekend to ponder my options. I considered getting a Milltek header, a RMW shorty header, or a complete Milltek exhaust system, which all requires that I consider the longer time horizon what I want my Mini to be. Right now I am very happy with it including the stock header and one ball exhaust. I do not want to invest in a header and only regret later should I decide to give Mini a big valve head. So for now I really just want to repair the stock header and give myself more time to ponder what, if any, after market exhaust system is best for Mini.

Milltek in UK makes one of the highest quality header for the Mini

Milltek catback exhaust also has unparallel quality and details so rarely found in aftermarket exhaust - like no cutting corner with the 4 point mounting using the factory support points

the Milltek header side by side with the factory header

Lessor in quality and more expensive is the RMW Shorty header. Its catalytic converter is reported lesser reliable than the German one used by Milltek. However it has longer runners and port opening that matches the exhaust ports on their big valve head. This would be the header of choice should I want to take the Mini to the next level of power.

RMW Short Header

The cost difference with buying a new aftermarket header versus repair the broken one is about 10:1. The performance gain in my estimation is 2-5 horsepowers max from what I infer, and that is with the best of design, unless you also make enhancements to the engine and the muffler.

Decision, decision. I was torn as if I should attempt to MIG weld the header or go seek professional help. Since it is stainless steel I was thinking of going to one of the stainless steel sheet metal fabricator to have it TIG welded. But reading that there is no reason you cannot MIG weld it if you don't care about compromising the corrosion resistance a bit. My thought is at the temperature of a catalytic converter the difference may not matter much.

Still, I have never attempt to weld SS and my MIG welding skill sucks. My biggest fear is to blow through the little bit of material and I would be hosed. I decided to take it to Dynasport a forum member suggested.

I can use a ramp like this in my driveway

many gen 2 new Mini's and a fat gen 3

the gen 3 fat Cooper S is bigger than the red M3 parked on the street; that is why I call them Maxi

I could not determine if they will use TIG or MIG but I made the appointment anyway. I wait around for the work to get done and was a long wait before the guy that will do the welding arrives. He was in a foul mood and kicked me out of the shop citing insurance concern. I didn't even have a chance to discuss what he was about to do. I sensed the situation and decided to give him the benefit of the doubt, since the price is right. All I could tell is he did the welding with the header in-situ - something that I cannot do without a lift. I could see from a distance that he MIG welded it. He spent a full 45 minutes working on it so it was not a easy welding work. At the end he has a helper sitting in the Mini to run the engine while he locate a couple of pin hole leaks which he add a dab of weld bead to plug them up.

I didn't get to see what he has done until I got home and put the car up on jack stands. It turns out he bridged the external mild steel heat shield and the header pipe - something I would not have considered. In retrospect I appreciate this approach as there is very little material left on the pre-cat side. I did wonder for a few moments the potential danger of welding shut a small pocket of air there. A high pressure bomb?

here is before the weld repair

Actually with the heat of the welding, there is very little air left in the pocket so I am not too worry. Sometimes, one can over-analyze a problem, and a bit of think out of the box this shop did goes a long way. The service adviser Devin who is very nice told me this is a very common failure, and they do this about once a month.

Mini is made whole again and it is running great again. I checked the muffler tips and there is a deposit of black soot resulted from driving the Mini about 10 miles all together after the header broke. This is due to the post catalytic converter oxygen sensor reading too lean due to air being blown in causing the ECU to think the engine is running too lean, and increase the fuel enrichment to protect the engine.