monocoque chassis repair

[Spot the welders dog]

Beginning to access this years jobs on the coupe and thought I'd start with the repair of the chassis rails.
Have any of you experience with this?
I am uncertain as to the best way to approach it.

The rust is on all sides, there is also a partial secondary inner support (visible in pic 2).
Would it be safe to cut the whole section out in one?
Is it possible the rails/floorpan would move without a brace installed, and where would you fit the brace?
Should I just tackle each section individually one plane at a time?

 

[ibrooks]

Difficult to say what might or might not move without a bigger overview of the structure.

Generally cutting it all out in one is a no-no. You usually have to tackle this type of thing almost like an archaeologist and peel back/remove one layer at a time. Partly that's so that you know/understand how it went together in the first place so you know you are replacing like-for like and partly it's because you need to cut away more of the top layer than the bottom so that you can replace the bottom/inner layer (you've got exposed edges to overlap your repair piece with and weld to). Sometimes that unavoidably means you are removing good metal from the outer layer in order to expose all the nasty stuff below but "them's the breaks".

Iain

 

[Jan]

There's some serious rot there old chum. And once you start to chop it out you'll find at least 3 times as much again! You will need to remove as much weight as possible from the old girl so that she can withstand the strain with what's left after you've removed the 'spit and bailing wire' that's currently holding her together.

I think you may need to first remove the doors and weld in some serious struts to help support the 'chassis' while you find out how little will be left after all the old rails have been removed. However a complete series of pictures and measurements should be taken before that so you have a frame of reference as to what goes where and what each bit does so that they can be prefabricated on the bench before tweaking into place.

These are the kind of jobs that we all aspire to, but rarely bother to start once we realise just how much nit-picking detail and tedious attention to detail is absolutely necessary!

 

[Spot the welders dog]

Iain, I too am wary of cutting into the rails, yet thought I would pose the question after seeing new rails are available. Pondered as to how these repair pieces would be installed without the need for a scaffold yard full of bracing, which led me to thinking I could 'get way' with less

Jan, why do I feel like you've kicked me down, let me crawl up on my knees, then went in for the kill
Was this a plan you and the GF hatched to make me scrap the project?

On a more upbeat note, i've found a pictorial diary of the same repair having been done by irishwoody which I had forgotton about!!!
Down side is I'm working on my back, and not in a warm garage with the car upon a spit.

 

[steveo3002]

ive seen bits like that cut off with no braces , youd have to think a bit where you put the axle stands , but the other side and sill etc should keep it together imo

once its tacked on , check all the door gaps etc are still nice , infact id prob not be opening the doors if u can help it

 

[Jan]

I believe in never kicking a man when he's down. He may get up again before I've had the chance to leg it Anyhoo ... leaving the doors on for support may not be enough. There will still be some play so that once everything's stitched back together again you might not be able to open them again! The annoying thing is that I have some similar (but fortunately not as much) work to do on my 1976 Silver Shadow. At least it's just the floor (so far), but it's all just above where all the underfloor mounted braking system components are sited and may involve the removal of all of them first

 

[Spot the welders dog]

Jan you'd better hope that it's just the floor you have to fix, 'cos if I see a thread with your name on it....

Steve: cheers for that; I was thinking along the similar lines if the need arose.
Having had a better look earlier, the repairs look alot less daunting than I first thought. I mighr re-instate the door brace again though - just_in_case

 

[Spot the welders dog]

Unpacked the welder form its hibernation and reinstated the door bars.
Before I start hacking away bits I would welcome any suggestions towards cutting the (left hand) vertical piece up to the flange. Behind the section is an inner support that needs to remain untouched, therefore I cannot plunge a slit disc in, or use it 'on edge' as it will contact the floor before the cut is finalised - am I making sense?
I'll try a picture

(Green is the inner support, red is cut line)

Any tool/process that comes to mind would be gratefully received?

 

[ibrooks]

A dremel type machine with a cutting disc is surprisingly useful in situations like this. A decent one will make fairly short work of surprisingly hefty steel whilst giving you plenty control on how deep you cut. A flexible drive for said machine is also a very good idea as it means the business end is that much less bulky when you are working in corners like that.

I've recently stoped borrowing my mother's Dremel (she complained that it was always in my workshop and never in hers) and bought myself a Ferm equivalent which seems every bit as good. Machinemart do the same tool as mine but badged as a Clarke.

Iain

 

[Spot the welders dog]

Iain thank you. I did have in mind such; although having only used one briefly some years ago I seem to recall that the blades where very easily broken.
Are there any recomended type/ brands of blades that perform well in a buffoons hands for such a task?
Yes, the flexi drive sounds a useful adaption to have also.

 

[ibrooks]

Err no - the ones I was using came in a Dremel branded accessories pack and I never got to the end of them. I've then started on the ones that came with the Ferm which again seem comparable. They don't last too long as they are only around the size of a 10p piece and they are really thin but if there's room for something bigger to fit in I tend to revert to the cut-off tool on the end of the air-line so it's only where you are really restricted for room that you use them and there's loads in the little tube.

Item number 350976738944 on fleabay is the same set that I've got. I prefer the way the Dremel drives the flexi-drive but apart from that I'd say they are much of a muchness so let the price sway your decision to buy or not (and shop around because that one I've given the number for is just the first one I came across).

Iain

 

[Spot the welders dog]

Thanks again Iain.
Have been looking at that exact same item, although to my mind It really should come with two 3.2 collets. Quick search hasn't returned any collets at UK outlets. I was momentarily seduced by the Proxxons' : perhaps more than I need. Also looked at a Dremel (4000) with a flexi drive (almost three times the cost of Ferm and only 1 year warranty), which comes with an "inspiring welcome poster"!

The diameter of the flexi drive head is another factor stopping me from buying anything yet. Keeping the wheel perpendicular to the cut is key, or so I've read: and probably explains why I took a dislike to the tool the first time. Yet without another solution I guess I really should just buy a tool and - buy loads of cut wheel or adopt a little finesse

 

[ibrooks]

to my mind It really should come with two 3.2 collets.

Mine did. So you can use a 3.2mm bit in the flexi-drive.

Iain

 

[Spot the welders dog]

Ah that's good to hear. Did you buy from this source? Think I'll pop the seller a Q&A.

Thank you...

 

[ibrooks]

I think so but yes probably best to ask the question.

 

[Spot the welders dog]

Ferm tool delivered today so thought I'd have a go at the chassis. Took five of the tiny discs to get through. Happy enough, although I was a bit lazy in not getting the drill out for the two spot welds.

Thanks Iain, you were correct: Two 3.2's!