Repairing rusted chassis rails Mazda MX-5 NB
One of the well-known ailments of a Mazda MX-5 NB and NBFL (2nd generation) are the sills (chassis beams) in the wheel arches. These suffer immensely from rust..
When the garage tells you after a service or MOT that the chassis is rusted, you are naturally shocked. Your beloved car couldn't possibly be completely rusted through, could it?
How does the rust occur and why doesn't an Mx-5 NA (1st generation) suffer from this?
The rust is caused by the design of the sills chosen by Mazda. The Mazda MX-5 has double-layer sills, which is good for strength in the event of an accident and the rigidity of the chassis. Unfortunately, it also has a downside: water can get between the two layers and then can't escape... Stagnant water that can't drain, you guessed it, will rust!
The MX-5 NA (1st generation with pop-up headlights) does not suffer from this at all because it only has one layer of steel in the sills. As a result, water is not 'trapped', meaning they will hardly rust, if at all.
Let me start with how, in our opinion, it absolutely should NOT be done.
1. A so-called cheap MOT solution: Welding a plate over the rust to make it 'solid' again and pass the MOT.
With this method, you postpone the problem and most likely will have trouble again at the MOT next year. This is a (bad) stopgap, not a solution.
2. Partial repair: Grinding away the rusted part and welding in a new plate.
The rust has probably largely been replaced, but even here it is not the solution. There are still areas with double-layer steel that will rust through sooner or later.
How LucaCarMods performs this repair
As stated, it is important that all rust is removed and cannot return. The solution is to remove all double-layer steel from the front chassis beams and replace it with a repair panel which, just like the Mazda MX-5 NA, consists of only one layer of steel.
For this rust repair of the chassis beams, we start by disassembling the front bumper, crash bar, headlights, wheels, radiator, power steering, and many other items that are in the way. During the repair, the engine can remain in place, but many ancillary parts are removed. Subsequently, the engine and fuel lines will also be wrapped with a fire-retardant welding blanket. Safety is paramount for this repair.
After most of the dismantling is done and the important parts are wrapped, the grinding can begin. This can look quite drastic as a fairly large piece will be cut out of the chassis beams. What is often even more drastic than the grinding, is the rust that appears minor from the outside but is already quite advanced on the inside.
Subsequently, everything needs to be thoroughly cleaned so that it is free of old coatings or wax layers. These easily catch fire and also result in a poor weld. Once everything is clean, the repair panel can be fitted to the Mazda MX-5 NB. Here too, you have two ways to do it. A weld where you overlap the panels or place them against each other with a gap of approximately 1mm in between. We always choose the latter option for good penetration, better aesthetics, and the steel being only 1 layer thick everywhere.
To distribute the heat during welding, short welds are made repeatedly, then you jump to another spot. This prevents warping and reduces heat in the engine bay paintwork.
Finally, the most important step: applying a good moisture-resistant coating both inside and out. Inside the chassis beam, we use Dinitrol 1000, which is a cavity coating, and on the outside, a robust Dinitrol 447 anti-chip coating. The weld seams and other seams where moisture or dirt could potentially get in are sealed with a body seam sealer.
After this, the MX-5 NB or NBFL is good for many years of driving pleasure!
If you want us to carry out this repair, please feel free to contact us! The cost you should expect is approximately €1095.00 Incl. VAT
Of course, you can also perform this repair yourself with our repair panels, which you can find below.
