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Getting back to it and straightening a bent chassis
#1
Hello Friends,
 
I've largely been off the forum for a few years, for various reasons.  I'm now getting back on to a project i started nearly ten years ago and I'm afraid I'm going to be asking questions again! (I know how much you all like answering them really Smile  )
 
I have a 1932 LWB chassis, for which I've been gathering c. 1932 components to suit.  When I left off my labours the last time I had got the vast majority of the bits to make a rolling chassis, many of which I had rebuilt/refurbished.  I'm tantalizingly close to the start of the "spanner work", to the extent that I've (perhaps ambitiously) cleared out half the garage and put the chassis onto axle stands!
 
At this point, one expects to find the things one hadn't expected, and so here's my first:  I've managed to bend one of the chassis rails!  When I got it, the top of the o/s chassis rail was corroded very thin, with even a few holes.  I cut this out and welded in some new steel.  As a rooky welder I didn't appreciate that the heat would distort the chassis.  On a flat surface, the o/s damper mounting now sits 1.5" off the ground...
 
I would welcome any advice as to how to sort that out.  I have in mind to use a large section timber fence post, some webbing straps and careful application of a 2 tonne jack.  Is that a sensible approach?  All suggestions and advice will be gratefully received.

Thanks!

Geoffrey
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#2
Well, that would certainly bend the rail, but if, as you say , "you were a rookie welder" will your welds stand up to the test? I think the answer is :- Have a go and diligently check your welds afterwards. I don't think that heating will help as you would have to bring such a large area up to red heat, that you may induce more problems. After straightening, check the diagonal distances between the front of the chassis and the damper bolt holes. And good luck.
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#3
I can imagine 3 possible outcomes (1) it bends as you hope (2) it doesn't bend at all (3) it bends locally rather than gradually and gives you a wonky rail ... or perhaps (4) there's a sickening crack and chunks of rust on the floor. Not sure I have a better idea though, nor even that the 'take it to a pro' option exists nowadays. Failing the above find a scrap chassis with one good rail?
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#4
An inch and a half is a long way out, presumably the spring mount is similarly canted and the car would ride oddly. Perhaps, if you have welded a new top right down the rail you have to accept that it's scrap and get a new rail or chassis. This was usually a problem when folk boxed in the bottom of the rails but even then 1/2" to 1" was the normal bend. If you are rather wedded to this particular rail you could either cut the repair off and have another more considered, compensated, go at stitching a new plate in. Alternatively you could heat it right through by embedding it in a fire and levering it against two very fixed solid objects while checking that the channel rail width doesn't open up or close too much.

I hope you're successful!

Dave
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#5
Dear All,
Thanks for your swift replies. It's sounding a bit ominous then... I did think this would be a test for the welding - possibly a good thing to make sure it is strong. I put in a lot of practice making a club fender for my fireplace before attempting the chassis welding, so I think the actual welding bit was effective - it was the likelihood of warping which I was too inexperienced to foresee. I will give it a go and report back.
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#6
If I were doing this job, and I am no expert, I would remove the old repair and start again by clamping the chassis securely to a flat surface and re weld a new repair piece in place by a series of small tacks on alternative sides / opposite ends filling in the gaps between the tacks progressively instead of making one continues  weld.
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#7
(14-05-2018, 01:31 PM)Phil Kingdom Wrote: If I were doing this job, and I am no expert, I would remove the old repair and start again by clamping the chassis securely to a flat surface and re weld a new repair piece in place by a series of small tacks on alternative sides / opposite ends filling in the gaps between the tacks progressively instead of making one continues  weld.

I'd go with the way Phil suggests - other than clamping the rail over something (a big RSJ with G clamps) to give it a slight bend in the opposite direction. Lots of stitches with many coffee breaks in between.
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#8
The chassis I used for our new supercharged single seater was distinctly bowed between the front engine mountings and the first cross member. In addition it had several large holes drilled into it plus three cracks. Clearly a previous owner was a a bit of a fatty who liked to use his electric drill.

I solved the problem by clamping a length of 40x40x2mm into the underside of the chassis rail using some big C clamps. I then welded these into position with 1" tack welds underneath. I had previously drilled out all the holes and run a thin angle grinder blade through the cracks. The square tube and inside of the rails were well coated in Wurth zinc rich weld through primer and I used this primer to slide the tube into the rail when it was all still wet.

I then welded the holes closed by welding the chassis rails to the new box tube underneath, did the same with the cracks. As this was going to be a special on a chassis acquired by Dad nearly 50 years ago, plus I made new engine mountings as I offset the motor, I didn't worry too much about originality in the aesthetics so this solution might not work for everyone.

In the light of your current situation, I'd cut out the repair, then use a section of box tube to hold things straight. Once this is clamped and things are straight you can begin to replace the cut away section of the rail. In your shoes I'd then weld the box into the underside of the rail and the repair to the top of the tube. Once all is straight and welded, I'd then carefully cut away the bottom of the box tubing flush with the underside of the rail. Then weld the edges to the underside of the rail. Now drill the engine mounting holes in the box tubing by just drilling directly through the old holes.

Simple and the Wurth primer will ensure that it doesn't rust and seam sealer will keep the water at bay

Ciao
Greig

Sunny South Africa
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#9
Pre war repair manuals are full of the sort of jacking tricks suited to amateurs. The main problem is finding the solid places or masses of metal or wood to jack against.  Lintels and floor beams are handy. (I used to prop i.f.s cars against floor joists to check bump steer but was always worried about the lounge floor springing a foot high bulge. )
Presumably the chassis top has shrunk. If brute force jacking cannot be contrived, a series of saw cut slots across the top , the chassis pulled and clamped flat and rewelded, would not use much electricity and the important flange area not weakened .
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#10
Yes the same thought occurred to me yesterday - would be a lot easier to make a series of lateral cuts and re-weld than to take out the patch altogether. As a rather amateur welder myself I'm not sure I'm qualified to say whether it's a good idea though.
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