A couple of MSA Cage Questions!

[simonr]

I know this has been done to death - but having read the blue book section K and the AWDC accompanying notes http://awdc.co.uk/index.php?option=com_content&view=article&id=154:challenge-rollover-protection-from-2011&catid=47:technical-updates&Itemid=72 I have a few questions!

I've mailed some questions to Vic Palmer (Scrutineer) which he is going to raise with the MSA, but these may just reflect my lack of understanding or knowing which regulation supersedes which.

I have read in a few places that welding light tabs, CB antenna mounts or 'challenge wings' to the roll bar is now prohibited. I have no issue with that. However, in the link above, Drawing 1 shows the minimum requirement of just a single B post hoop with stays. Does this mean that anything else, for example the extra bits on Drawing 6, are not subject to that ruling? Or is it the case that any structure you add which might be considered to be a part of the cage cannot have anything else welded to it? Does that include body panels?

What I was considering (hoping) was that I could build an internal hoop to Drawing 1 and connect it to longitudinal external hoops which pass over the doors as per Drawing 6 in the Blue Book. Drawing 7 in the blue book looks more like drawing 6 in the link above? If these are not considered to be a structural part of the main ROP system, the wings, door bars and rear surround can weld to them.

Mounting to the Chassis.

In the link above (section C part iv) it says that the main hoop must be mounted directly to the chassis and refers to Blue Book Section K App2. This shows that although the cage can be bolted in place, it's necessary to weld the foot mounting to the chassis. I have spoken to VOSA who say that if I weld roll cage mounts to the chassis anywhere between the front and rear spring hangers, the vehicle must be submitted for inspection / IVA. The reason is exactly the same as the MSA requirement not to weld CB antenna mounts to the cage - that the weld causes a potential stress concentration, possibly leading to fatigue failure in the middle of the chassis where the bending moment is at it's highest. In the case of a monocock chassis, welding spreader plates to the shell is less of a problem because the stress is much more distributed and it's less likely to cause a fatigue failure in one place.

Is it thus the case that to attach a cage which complies with the MSA, the vehicle must also be submitted to VOSA for inspection if it is to retain road legal status?

My suggested solution is to make a clam-shell mount to which the cage is welded which clamps around four sides of the chassis rail, secured with bolts. To my mind, this provides as secure a mounting as the cage foot being bolted to a spreader plate and avoids an IVA inspection. I've raised this one with Vic Palmer - so I may get a qualified response from the MSA in due course.

I don't want this to be seen as a dig at the MSA nor their rules - more a route to enlightenment!

Si

[Daan]

I know this has been done to death - but having read the blue book section K and the AWDC accompanying notes http://awdc.co.uk/index.php?option=com_content&view=article&id=154:challenge-rollover-protection-from-2011&catid=47:technical-updates&Itemid=72 I have a few questions!

I have spoken to VOSA who say that if I weld roll cage mounts to the chassis anywhere between the front and rear spring hangers, the vehicle must be submitted for inspection / IVA.

Do you have that rule black on white?

Because if that was true, virtually every alteration you do to a landrover chassis would be illegal. You can fit defender outriggers to a disco chassis and fit a complete defender body without going for the IVA. Whether it saves you going to an inspection, not sure, but so long as you dont cut the chassis that should all be perfectly legal.

Daan

[simonr]

Do you have that rule black on white?

Black - on Grey!

Replacing outriggers like for like is OK because the manufacturer will have carried out the stress analysis with them in place. Welding on something new that the manufacturer could not have considered is quite different. They brought up Land Rovers recall of 130's fitted with Hiabs where the chassis was capable of withstanding the static load, but they were snapping in the middle due to fatigue around a stress concentration at the mounting points. I'm not convinced even VOSA are qualified to assess whether a fatigue failure will or will not occur - but I guess they have a better chance if it's inspected than not!

Si

[ricky tango]

hmm i'd also be interested in an answer on the cb mount and light bar tabs question as im about to get a rrc msa internal external , but the only bit scrutinised for its structure is the rear hoop and stays,

the above ruling on no fittings to be welded to the msa scrutineered part of the cage has however now scuppered my plans on welding some mounts to the rear hoop back stays to mount my waffles tho

[western]

are you going to compete with the MSA cages, if no, then there shouldn't be any problem.

MSA Blue book section K

[simonr]

are you going to compete with the MSA cages, if no, then there shouldn't be any problem.

If not, making an MSA compliant cage is a bit pointless? I could tape on any old climbing frame!

I have a vehicle which I want to make fully MSA compliant and keep it fully road legal. Competitions in the UK, with some exceptions, require one or the other. My previous vehicle (now a big pile of lumps of scrap metal) was neither which prevented me from entering the things I wanted to (not withstanding the odd reliability issue!).

Mr Tango, I wouldn't weld your waffle mounts to the rear stays - I totally agree with not welding to structural members. There are plenty of plastic & metal tube clamps available which will serve the same purpose without welding.

Si

[najw]

I have read in a few places that welding light tabs, CB antenna mounts or 'challenge wings' to the roll bar is now prohibited. I have no issue with that. However, in the link above, Drawing 1 shows the minimum requirement of just a single B post hoop with stays. Does this mean that anything else, for example the extra bits on Drawing 6, are not subject to that ruling? Or is it the case that any structure you add which might be considered to be a part of the cage cannot have anything else welded to it? Does that include body panels?

Where have you read that Si? There is no reference I can find in MSA regulations to that effect.

I think its another Chinese whisper. If it were the case that nothing can be welded to the cage then most Comp Safari racers would not comply.

However if it were the case then it would only apply to the parts of the cage that were subject to scrutineering. Anything else you choose to hang off your cage would not be scrutineered.

Nothing can be considered to be part of a cage over and above what is in the drawing/requirement.

Incidentally for KoV Drawing 6 is the minimum requirement.

[simonr]

Where have you read that Si? There is no reference I can find in MSA regulations to that effect.

I think its another Chinese whisper. If it were the case that nothing can be welded to the cage then most Comp Safari racers would not comply.

You're right, it may just be hearsay - I'll see if I can find a reference. Having had a look, there is a reference to fixing a metal roof to a welded on flange - so it must B******s. I think I read it of Difflock or Devon. Goes to show that you cannot believe what the interweb tells you!

Is Drawing 6 in the blue book misleading? The drawing looks like it has bars surrounding the doors with transverse braces at the top? This contradicts the "one continuous length of tubing must be used for the hoop member...". It also says "Note: Diagonal may be handed to left or right" whereas Section 9.19 f says "Diagonal struts - these should be fitted such that the upper forward joint is on the drivers side of the vehicle". I suppose both could be correct depending if its left or right hand drive. The drawing really ought to refer to 9.19 f if so.

Si

[markyb]

Neil when we did the AWDc challenges in think 2001 i did my cage then with nothing welded to the tube as I too was under that impression that nothing should be welded to it but never was there and i had mine inspected by MSA guy for log book

[dirtydiesel]

You're right, it may just be hearsay - I'll see if I can find a reference. Having had a look, there is a reference to fixing a metal roof to a welded on flange - so it must B******s. I think I read it of Difflock or Devon. Goes to show that you cannot believe what the interweb tells you!

Is Drawing 6 in the blue book misleading? The drawing looks like it has bars surrounding the doors with transverse braces at the top? This contradicts the "one continuous length of tubing must be used for the hoop member...". It also says "Note: Diagonal may be handed to left or right" whereas Section 9.19 f says "Diagonal struts - these should be fitted such that the upper forward joint is on the drivers side of the vehicle". I suppose both could be correct depending if its left or right hand drive. The drawing really ought to refer to 9.19 f if so.

Si

I think it's b******s, within the arc the specified mounts for rear harnesses weld to the rear stays.

drawing 6a is only one permutation of the minimum requirement, i believe both front hoop and side bar designs are permissable.

The rules are vaugue at best i've taken the diagonal rule to mean that it must have a diagonal and they'd prefere it to be where 9.19 says.

The absolute best thing to do si is to get yourself to an awdc comp and have a word with a senior sruteneer. i once had a very long chat with the chief scruteneer for the awdc (robbo aliperti?) it was enlightening to say the least.

[simonr]

The absolute best thing to do si is to get yourself to an awdc comp and have a word with a senior sruteneer. i once had a very long chat with the chief scruteneer for the awdc (robbo aliperti?) it was enlightening to say the least.

I actually attend quite a large number of AWDC events each year - which is where I know Mark & Vic (the Scrutineers) from. However, I don't like overloading them with questions as they are obviously busy. Posting some of them here first means that, for things like the welded on bits, I don't waste the time they can give me.

Si

[simonr]

What I proposed for a clamp on cage mount is this:

The closest to it in the MSA Blue Book is Drawing No 33 / 59 - but both appear to need to be welded to the chassis.

It states that each foot must be attached by at least three 8.8 Grade M8 bolts - which should require about 88kN (8.8 Ton) tensile force to break them (and about 50kN to shear). The requirement for strength given by the blue book id 7.5 vehicle masses longitudinally (pushing the cage backwards against the rear stays). Assuming the rear stays act as a fulcrum and the load is split equally between the main hoop feet - that gives an approx tensile force on the bolts of 94kn (for a 2.5 Ton vehicle). Therefore (This is a back of envelope calculation and the force distribution in practice will be different - but I think it's likely to be greater rather than less, particularly for a corner impact) the minimum of 3 x M8 bolts at best is only just strong enough.

A clamp-on, tightly fitting mounting, with 6 or 8 M8 x 8.8 bolts, even made out of 3mm plate should be stronger.

Si

[Daan]

What I proposed for a clamp on cage mount is this:

The closest to it in the MSA Blue Book is Drawing No 33 / 59 - but both appear to need to be welded to the chassis.

It states that each foot must be attached by at least three 8.8 Grade M8 bolts - which should require about 88kN (8.8 Ton) tensile force to break them (and about 50kN to shear). The requirement for strength given by the blue book id 7.5 vehicle masses longitudinally (pushing the cage backwards against the rear stays). Assuming the rear stays act as a fulcrum and the load is split equally between the main hoop feet - that gives an approx tensile force on the bolts of 94kn (for a 2.5 Ton vehicle). Therefore (This is a back of envelope calculation and the force distribution in practice will be different - but I think it's likely to be greater rather than less, particularly for a corner impact) the minimum of 3 x M8 bolts at best is only just strong enough.

A clamp-on, tightly fitting mounting, with 6 or 8 M8 x 8.8 bolts, even made out of 3mm plate should be stronger.

Si

3 M8 bolts works out at 63kn in my view, and lateraly you only need 2.5 x vehicle mass in that direction. 7.5 times from the top coming down and 5.5 times fore and aft. Anyway, these requirements only come into play if you homologate a cage, so do not apply to you I dont think. I wouldnt use a clamp on bracket like that on my cage fittings, as it would pointload the chassis badly and trys to compress the box section. The welded versions allow you to spread the load more evenly and actually reinforce the chassis. What I can say though is that the issue with the MSA rules is that they require you to weld 6mm plate to a 2mm chassis. That is proper dog poo engineering! Daan

[simonr]

Trouble is, if you follow VOSA's rules, you cannot weld to the mid section of the chassis without an inspection. I know most people don't - but in the light of Gresh's experience - this is going to fully comply and I have to act on the best advice I'm given.

I agree that it increases the point loadings on the chassis rails which may cause deformation - but it's unlikely to break free of the chassis.

The strength calculation of bolts comes from here: http://www.tribology-abc.com/calculators/e3_6e.htm. I've based it on the Ultimate tensile load - whereas your figure I think is closer to the Max tensile. I used this as a best possible case rather than a safe load.

Could you suggest a better clamp design? Even if you personally wouldn't use it?

Si

[CwazyWabbit]

I know this isn't quite what you were asking Si but would you not also be worried about the bent lip of your clamp that you are bolting through bending under load? Would it be better to weld tubes/drilled bar to the side of the bracket to bolt through eliminating the chance of bending of the lip and the subsequent loosening of the clamp?

[Bowie69]

With that clamp design, I think you will struggle to ensure sliding forces in the rear stays, for example, didn't just allow it to move along the chassis rail.

The other thought I had about bolt fixing would be to drill, fit crush tubes and bolt it through the chassis, 6mm plate either side, with the top plate sitting tight to the chassis above it.

I suppose a lot of the regs are there so they allow proper inspection of the mounts -it's easy to see a 6mm plate welded to the chassis, and easy to see the 4 M10 8.8 bolts holding it in place, not so easy to define or see how a bolted fitting should look, or whether crush tubes are present and indeed fitted properly.

[simonr]

From VOSA:

Your vehicle will need Individual Vehicle Approval (IVA), Single Vehicle Approval (SVA) or Motorcycle Single Vehicle Approval (MSVA) if:

it has less than eight points

it has a second hand or altered chassis, monocoque bodyshell or frame

there is evidence that two vehicles have been welded together to form one (eg ‘cut and shut’)

If your vehicle passes you will be able to register your vehicle and will be given a ‘Q’ registration number.

An 'Altered Chassis' is considered to be one which has had new parts welded to it in the region between the front and rearmost spring attachment points, differing from those originally fitted to the chassis by it's manufacturer and as it was originally submitted for type approval. Same goes for removal of parts of the chassis - and may include drilling of holes where they may compromise the strength.

I'd say that's pretty clear cut! If you weld cage mountings to the chassis, it is an 'Altered Chassis' and subject to IVA.

Si

[Retroanaconda]

Well that's half the UK's competition trucks off the road!

[Les Brock]

What only half......

[simonr]

Well that's half the UK's competition trucks off the road!

I've had a call back from VOSA - with some good news! They say that welding a safety cage to the vehicle is OK so long as it is a requirement of the MSA (or other regulating body) and ONLY the safety cage with nothing else attached to it other than harness mounting points - as they are part of the safety system.

Challenge wings, lights, waffles, shock absorbers, curry hooks - anything which is not specifically related to the safety of the occupants is subject to IVA. I wonder if this is where the 'Chinese whispers' about such things has come from, VOSA not MSA? He also said very specifically that bob-tailing is out. I was pleased and surprised that he knew all about Land Rovers - and what we get up to in them!

Si

[Bowie69]

Good stuff Si, nice to have it in black on pale blue

bob-tailing is out.

You mean it's IVA time, right? Because I have spoken to VOSA on this specific subject recently, and they were fine about it, just you need an IVA at £450, £150 retest fee.

[simonr]

You mean it's IVA time, right? Because I have spoken to VOSA on this specific subject recently, and they were fine about it, just you need an IVA at £450, £150 retest fee.

Yup - he said it's the most common LR query and the answer is an absolute - "It must be IVA'd"

Si

[Retroanaconda]

But chopping the rear crossmember off a Disco chassis and putting a 90/110 one on would be OK, as it's outside the specified wheelbase area (ie. behind the rear spring mounts)?

[Steve Hiatt]

I think its another Chinese whisper. If it were the case that nothing can be welded to the cage then most Comp Safari racers would not comply.

As Neil says. Everything hangs off my roll cage as it's a space frame and I've never had an MSA or FIA scrutineer query it. We are advised to weld tabs to mount bodywork rather than rivet to the cage, which is a no no.

[Bowie69]

But chopping the rear crossmember off a Disco chassis and putting a 90/110 one on would be OK, as it's outside the specified wheelbase area (ie. behind the rear spring mounts)?

Negative! 'Radically altered'. Not to mention the bulkhead outriggers that need adjusting to fit the new bodywork.

IVA required.