Mk2/2.5 chassis rails, are they being repaired correctly?

Technical Area Body, Interior & Styling
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First off, I’ve never owned any of the 2nd generation iterations. Secondly I’m not a qualified car engineer. Right, with that out of the way,  I’d like to know about the chassis rail repairs that have become very popular on these cars. My understanding is the original rails are thinner metal but double skinned, acting as a crumple zone in the event of a collision, absorbing a lot of the energy from an impact thus protecting occupants of the car. So, from what I see and hear about the repairs being undertaken, it’s the double skinned sections that get water in between and eventually, corrosion renders them dangerous. Which is a real shame as many cars have been scrapped when they are (look) excellent cars in other areas. The solution appears to be, welding in new sections of metal after cutting out the rot, using single skin metalwork. Sometimes prefabricated sections, sometimes made up metalwork in the shop.

My question (or point) is, these repaired sections are not the same as the original design i.e. single skin instead of double skin. Therefore, the original design of having a crumple zone in the chassis rails has been lost due to a dissimilarity between repaired sections and the original metal left in place. Was the original design brought about by ever more stringent legislation on car safety, I think it was. Are the repairs currently being undertaken, compromising this design? I think they are. These are only my thoughts put down in writing, not based on car engineering expertise. 

Having prised the lid off the worm can, am I overthinking this or do I have a valid point? I realise unrepaired cars are getting MOT’s due to the rotten sections not being easily seen due to the undertray obscuring this, also repaired cars are doing the same. 

Barrie

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Hi Barrie

No, your point is valid and the chassis legs would not perform in the same way if there were an impact.

Welded, solid metal works well for a repair. The area of the chassis rail effected is usually quite small. The bespoke sections replace all rusted metal and welding would do the equivalent of quarterising the margins, fusing the two layers together to form a seal to future water ingress.

The controlled crumple zone design of the original chassis rails would undoubtedly be compromised by these repairs in the event of an accident.

I wonder what solution the engineers came up with for the MK3 and MK4? - hopefully one that is more resistant to rust.   

When this was first noticed, I seem to remember it was the MK2.5 that caused the initial panic. At the time some of these cars were 9 years old and the only solution offered by dealers was engine out and new chassis rails. The rails themselves cost £400 - 500 each so a number of otherwise excellent cars with low mileage potentially worth £3000 - 4000 scrapped. It took a while for independent specialists to work out a repair strategy and develop the repair panels and even now MOT testers miss badly corroded chassis rails. I assume that dealers would be legally obligated to go the new chassis rail route for the reasons you have identified. Does raise the unfortunate question over potential litigation where chassis rail repairs get the blame for injury or death.                  

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Hi Barrie

You really do have a very valid point here, even more relevant to me as I did the repair and fitment of the MX5 Restorer supplied chassis plates myself, they are a good quality product and are certainly not designed to crumble as I see it. I have to say, when fitting the plates, this wasn’t something I even considered, well done mate.

Having been an MOT tester myself during part of my working life, all the testers I knew had a pretty good knowledge of issues specific to the different makes and models so I’m sure the rust element we’re discussing is pretty well known but I do agree that it is difficult to see the rails as you say. I would be interested in hearing what others think.

Rgs Geoff

 

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MoT’s aside, I also wonder whether insurance companies might use this as an excuse to not pay out on claims in the event of an accident. I have no idea whether the crumple function of the chassis rails was/is considered a fundamental safety feature or just a small part of the overall safety design package. If it’s fundamental then I would have thought a like for like repair would be required so as not to compromise function, otherwise insurance companies might well claim this reduces the safety of the car and hence invalidates the insurance if they’ve not been informed.

On the other hand, it may be a non-issue…

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Many here will be aware of the rebuild of our Mk2.5 a few years back. It was well documented at the time, so I will not go over old ground.

Suffice to say, our rails were beyond repair patches to the extent the engine mounts were pretty much bolted into God’s excellent air, and the ARB mounts were supported by the bushes.

In short, ours was so bad, a retired VOSA engineer we know locally essentially condemned our Sport as unfit for the road and dangerous. 

I drove it to it’s garage with considerable trepidation as one may well imagine. My wife took a taxi. I kid not.

Moving on, we either scrapped the car, or opted for essentially a re-manufacture restoration using, and here is the caveat, OEM Hiroshima sourced components.

 

And so… 

 

 

 

 

 

Another story for another day.

 

Here is the offside full rail section from Mazda. I appreciate it is difficult to see the construction, but it came as a surprise to note, as in the case of my Mk1, it is a very substantial single skin affair.

  

And here are some photos of the finished work.

 

This is some of what came out. Back in the day, ignorance was bliss, before people like me exposed the situation, even getting told to “wind our necks in” ( quote unquote) by an “officer” of this OC Club believe it or not. Cheeky little blighter. 

 

To conclude, I now have an extremely solid Mk2.5 with chassis rails that would not disgrace a Chieftain tank.

Crash protection? Well, if you front end a 5 that hard that it needs crumple zones…how long will your piece of string be that day?

You will be in serious trouble one way or another, but thankfully we have airbags. So, live in hope.

For the benefit of doubt, I informed my insurance with photos and technicals, and they felt it was not an issue. That wa one insurance company though. I’ve not bothered since.

Technically, I’m driving a Sport not as Hiroshima designed, but it does not prey on our minds.

My Mk1 would kill me on a head on with it’s nice steel and wood wheel, solid rails, no bags, and zero crash protection bar a seat belt.

 

 

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It’s a funny one if I owned an otherwise really nice mk2/2.5 that had this issue, would I get it repaired in the way that seems to be accepted, or would I scrap/break it? In my case, I’d get it repaired for sure.  However as others have pointed out, could this be a potential issue from an insurance point of view. Who knows. We certainly enjoy, in this country, quite a bit of “licence” when it comes to modifications and alterations to our cars. A few years ago, my heavily modified mk1 was at the MOT station and the owner had two German apprentices working over here for a few months by arrangement with a German garage. They were drooling over the modified car, explaining that nothing like it would be allowed in their country  The owner asked if I’d mind taking them for a spin in the car once MOT was done. Of course I obliged and they loved it!  So, these repairs are just accepted, perhaps no one has considered this as being detrimental, only better due to having new metal welded in. 

Barrie

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Wow! That’s an epic rebuild! A lot of time, effort and I presume money by the look of things? Amazing work. I know you said single skin replacement rails but pic 7 looks to show double skinned? Either way, fantastic job and much kudos to you for sorting it in the way you did.

Barrie

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Barrie, it’s an odd one. I cannot explain it.  

70/80% of these rails are solid, with what looked like strength sections welded in.

What I can tell you is they are bliddy heavy. 

They went into place with pinpoint accuracy however, with pretty much zero joggling required. 

At any rate, they are submerged in some sort of “stuff” they use on North Sea metals.

As are all the other nooks & crannies in this car…after new rear wings and sills.

It stank like an oil rig for weeks. 

Bonnet & front wings are original though. 

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I am very much impressed with your work  often folk consider selling/scrapping their pride and joy due to some potentially expensive rework, not just corrosion issues. If you get a quote for repair, are you better sticking with the devil that you know, or moving on but possibly have the same issues again, further down the line? A brave decision by you but what a car to have  safe in the knowledge it will stand the test of time, well done again! There cannot be many that have gone the route you did

Barrie

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■■■, and i thought i did a major rebuild on my 2.5 “respect” 

 

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d 

I will second that - had forgotten about this. Hopefully will last forever.

Looking at those rails I am struggling to see the crumple zone? It looks like solid mild steel with a short section where a second skin of equally solid steel is added.

My conclusion is there is no designer crumple zone and the short section with the reinforced second layer is the cause of all the problems. Given all the captive nuts and associated holes as well as no seal between the two layers, it is a recipe for disaster, especially as the underbonnet area on the MK2/MK2.5 seems to be a much bigger water attractant than the MK1.

Simply designing a chassis leg without that ill thought out double layer section would have avoided all these issues. The same conclusion applies to the poorly designed rear sill sections.      

 

13

 

It was, in my opinion, a bit mental to do Barrie. However, there is history behind the car. My wife’s mother paid 50% of it at the time of purchase in 2006 as a gift, and M-in-Law loved being wheeled around on days out, hood down, shades & sunblock in place…at the age of 86-odd. When she passed on, SWMBO had a tough choice. Either keep it in the family, chuck a few grand at it, or get a Mk3/Mk3.5. She simply did not like them…or the prices. It’s a bit like getting quality Barkers resoled. They just keep going mechanically if you cut the rot out. That car is just about to turn 100k, and has cost us buttons mechanically, and runs like a new one as I’m all over it’s servicing like a bad suit. I’ve only put new discs and calipers, drop links, a new exhaust and a few bulbs in it bar “by the book” service items but I change the oil/filter every 4k…and have drained the gearbox/diff for that expensive Castrol stuff.  What we did is not for everyone by any stretch, it’s just a matter of personal choice.   

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We appreciate everyone’s very kind comments. Kinda makes it worthwhile. 

As was the finished project which does get a few nods of appreciation at petrol stations etc… which put wee smiles on SWMBO’s face.

We know Mum is watching.

 

 

That is BMW lacquer incidentally. None of your soft Mazda wipe on…wipe off rubbish. 

15

Incidentally, SNO2 “Zoom Zoom” Xray is returning to the coachworks next month as poor SWMBO mashed the front apron against some new local kerbing.

Not to worry…I’ve a perfect spare nose in the loft.

I’m using the chance to de-badge the front bumper. In my opinion, looks better…smoother…less cluttered. 

In March, this is getting restored from this:

 

Back to how I bought it 14 years back. Yup, I’m mental.

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Having debadged  the nose of my car, I can recommend it!  Just gives the car a ‘smoother’ look. Regarding the mk1, if it’s turns out like the other car… Well what can I say, well jealous 

Barrie

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Roadster’s paint is actually only 4 years old believe it or not. It’ll come back up nice with a pro-mop. It’s got a low miles mill in it too, and God knows how many new mechanical parts.

Basically, new sills & rear wings, new coil overs, discs, calipers, exhaust probably…and maybe a new autobox…cheap as chips.

Why does it look so bad?

We had to shelve a few things to focus on our son who had a few “issues” on his last Afghanistan deployment but he’s great again…so just playing cstch up with “life” 

Time to wake up and smell the coffee. Hood down…sod it all!

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Very interesting thread.

For the groups who complete repairs (ie. replacing the front chassis rails), can any of you comment on the design of what you’re currently fitting, i.e. is it designed to crumple in a similar way to the original?

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The only ones I’ve seen are single skin.

Which does not mean to say sandwiches don’t exist.

I imagine lining up and joggling two double skins then welding internallly would require the flexibility of a stoat soaked in GTX.

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Barrie