Chassis welding required

[Cyffo]

Hello everyone,
I wonder can you offer me some advice/guidance?
There is a split on either side of the chassis (Compass Kensington) that look as though they would benefit from some attention, maybe by a welder. Are there specialist caravan chassis welders?
What would be my best course of action?
Here's a link to some photographs
http://www.olsm.me.uk/caravanpics.html
Thanks,
Cyffo.

 

[ProfJohnL]

I think you should check with the chassis manufacture, as I do know that some welding activity can change the ductility of the chassis material making it more vulnerable to damaged under normal loads.

 

[VicMallows]

A good local welder should understand the requirements and know the appropriate technique to use. I cannot imagine the chassis manufacturer being able (or willing) to offer any better advice, especially remotely. My first port of enquiry to find a welder would probably be a well established local engineering workshop or fabricator......or even a reliable local garage.

 

[Dustydog]

I think you should check with the chassis manufacture, as I do know that some welding activity can change the ductility of the chassis material making it more vulnerable to damaged under normal loads.

Prof
Could he use doubler plates although I appreciate it goes against the advice for not drilling holes in the original chassis??

 

[Cyffo]

Here's a link to a site where I've uploaded some photographs.
http://www.olsm.me.uk/caravanpics.html

Thanks for your advice everyone,
Cyffo.

 

[colin-yorkshire]

hi. they look like stress fractures radiating from the bolt holes. there was a thread a while ago by someone doing up a old van that had the same issue. it's been awhile so not sure how he sorted it.
it hard to see from the photos [no zoom] but it appears to be a AL-KO galvanised steel chassis.
it can be welded although not as easy as it may appear as the galvanising coat will not weld who ever does it should be competent in this type of repair it may need plating as well.
I would not think the chassis manufacture would help much.[if it is an ALKO I never found them very helpful when I made any enquiries] but it depends how old the van is but it may be worth a shot if it similar to a current model one thing is for certain unless you get it sorted it can only get worse.

 

[ProfJohnL]

Looking at the pictures, and the location of the cracks

The problem is mirrored on both side of the caravan.

Just considering one side, the two U channel chassis members are designed to make a close fitting interlocking form along the top edge, and in conjunction with the tension in the four bolts to create a joint with high friction to prevent relative movement in the plane of the joint. However between the bottom flanges there is clear air, which means the bottom flanges and their free side wall offer virtually no structural strength to this part of the chassis.

If the damage were stress cracks caused by towing, I would have expected to see similar issues with at other bolts of the four on each side. The pictures show no evidence of that.

However the last picture suggests is there is a some lateral movement of the cracked portion.

My initial thought was could this have been caused by jacking under this point? but I tend to discount that as the its unlikely the dead weight of the caravan would cause that much damaged to flange.

But considering where the affected area is on both sides, it seems conceivable to me that if the caravan had been towed over a hillock it might have caught this portion of the chassis and featured and bent in this manner.

It's bit of a mystery, but unlike Colin I don't think it will inevitably get worse, unless the same misadventure befalls the caravan. I would do something about rust protecting it

 

[DrZhivago]

A bit strange in that the crack is not really associated with the bolt hole. I would say the crack started from the front edge; it has almost by-passed the hole.

The Prof mentioned lateral movement and I think that's right. Because the bottom flanges are rather separate (poor design IMHO), the bottom flange of the rear beam, and an inch or two of the web above it (up to where the bolt has stopped it), has been allowed to flex in and out laterally, creating this fatigue crack. It could flex in and out because of lateral loads (cornering) or by a small degree of elastic buckling under more severe vertical loads (speed humps, pot holes).

I would simply get a steel plate made, say 4mm thick and preferably with a lower flange to hug round the existing rear lower flange, to bolt on the outside of this joint using the existing four bolts. Dont then worry about the existing crack, the new plate would stop the flexing. Make sure the chassis members are well supported with several axle stands before removing the bolts to do this. I would first put an additional bolt through the existing members halfway between the two forward ones to keep the beams held together while the others are removed - otherwise the two members could spring apart laterally or shift slightly and misalign the bolt holes. This additional bolt would be avoided by a cut-out in the front edge of the new plate. No welding involved.

 

[RayS]

I agree with the Doc on a possible solution. Perhaps too use a technique common years ago in metal structures. Drill a small hole using a sharp new bit ground to the correct angle for steel at the 'inside' end of each existing crack, such that the crack opens into the hole. This method can prevent the crack from propagating any more and also works on plastic materials e.g. caravan front and back panels.

 

[ProfJohnL]

To be honest I cannot see how cornering or any other normal loading through towing could possibly cause those pieces to to be stressed and start a fracture of that type.

In my opinion those two pieces are not under any load, they are actually superfluous the strength of the chassis.The only way I can postulate they have become bent like that is by the application of some abnormal force directly to those specific points. Something has got between them and pushed outwards. Could a caravan mover have been fitted badly? or has the caravan been towed across hillocks or sanddunes and got wedged and as it came to a halt the force was absorbed by thess pieces.

I know its speculation , but I'm trying to concive how that damnage could have arisen.

Howver it does mean the cracks arn't goint get worse, unless the same events arise, and as the functional area of the joint is unaffected, there is no need to add plates or weld, but the fractures do need to be protected from further corrosion.

 

[colin-yorkshire]

To be honest I cannot see how cornering or any other normal loading through towing could possibly cause those pieces to to be stressed and start a fracture of that type.

In my opinion those two pieces are not under any load, they are actually superfluous the strength of the chassis.The only way I can postulate they have become bent like that is by the application of some abnormal force directly to those specific points. Something has got between them and pushed outwards. Could a caravan mover have been fitted badly? or has the caravan been towed across hillocks or sanddunes and got wedged and as it came to a halt the force was absorbed by thess pieces.

I know its speculation , but I'm trying to concive how that damnage could have arisen.

Howver it does mean the cracks arn't goint get worse, unless the same events arise, and as the functional area of the joint is unaffected, there is no need to add plates or weld, but the fractures do need to be protected from further corrosion.

they are stress fractures John. not from towing but by being used as a jacking point.
Iv'e seen something like this before on boat trailers. I wasn't sure at first but since my last comment have copied the pictures onto a program that re pixelate's a photo so it can be blown up without distortion. there is clear evidence that a trolley jack has been used on ground that doesn't allow the wheels to turn.
as you know when a trolley jack is used it moves the wheels while lifting to maintain a straight lift when they don't move it lifts in an arc this moves the contact point outwards there is bending of the lower edge in this outwards direction. there is also crease marks on the inner edge of the lip on the chassis rail. [cannot be seen on the original] where force has been used to push the rail outwards.
if the damage had been caused by grounding these marks would not be there but there would be marks on the underside of the lip [lowest point] there are none.
I would deduce therefore that at some time in the past someone has jacked the van up with a trolley jack [probably more than once] on something like gravel. and bent the rail outwards causing it to crack under stress. and left it to go rusty.
providing this is not done again it could well be ok. but if it was mine I would just tap the deformation back weld the crack and give it a good coat of underseal. making sure the van is jacked up on the axle in future.
it may well be ok if left without welding or plating but why risk it. someone may just use it as a jacking point in future the cracked area would always be a weak point.

sorry. I cannot re produce the enhanced photo. I don't have the means to to do this.

 

[ProfJohnL]

Hello Colin Its certaily a possibility , though I originally discounted the thought, because the it was my judgement the sections would have be strong enough to support half the weight of the van without the damage observed. But I do agree it seems a possibility. It is more likely scenario that sand dune surfing.

I also conclude the damage is not going to affect the structural strength of the chassis at those points, so repair is not strictly necesary except to do some rust containment..

 

[colin-yorkshire]

yes I agree John those points are not structural and would not affect the integrity of the chassis as a whole.
and as such could be fine. but as a safe guard I would do something with them if only for my own piece of mind.
one day a roadside assistance mechanic or tyre fitter [most likely suspect] could cause more damage repeating the error.