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Puma rear crossmember improvements/recovery point?


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Hi folks - after a bit of help.

 

In a few weeks my puma 90 is booked in the body removed in order to dismantle, blast & paint the chassis and underbody components prior to reassembly - a mini restoration. The chassis is completely solid, so this is just preventative and will deal with the annoying surface corrosion.

 

However, the one thing that winds me up is the lack of a sensible recovery point on the rear crossmember - I love the look of a simple recovery eye bolted on, but am aware of how flimsy these late chassis are so would never do it. Up to now I've got by with a pair of Jate rings (fitted while the tank was out) but they're a pain to access.

 

There are bolt on options (a NAS rear step or a receiver hitch) but wondered if there was a simple fabrication mod that could be made to address the issue while the chassis is seperate. Maybe some bracketry that passes through the crossmember or some sort of sleeve attached to the chassis rails secured through a (new) crush tube on each side, something like that? I've even considered a custom made version of this to wrap around the crossmember attaching to each chassis rail.

 

Also aware of the spereader plates that are commonly used and have considered this - maybe drilling out the threaded nuts in the crossmember so fasters can pass straight though - again, thick crush tubes could be added.

 

any other ideas short of going the whole hog and fitting a dixon fabs crossmember?

Edited by twodoorgaz
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Here is the mounting plate and recovery lug I designed for my build. 12mm for the mounting plate, 20mm for the recovery lug. They get welded together. Then of course crush tubes in the cross member. 
 

Two of these, and the bolts are either side of the chassis rail. Designed to be used with a bridle.

 

 

9395DA6E-AD8C-4F5F-A4A2-4CF0547ECFD1.jpeg

20F0ADA9-6741-46C5-9445-906095D52B63.jpeg

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For competition use, the late Defender style chassis (Td5 onwards) must either use the full factory mounting points, i.e. using the legs back the chassis/tank area. Or jate rings.

If you are removing the tank, you could put a spreader plate behind the rear crossmember (min 3mm) and bolt all the way through, as per the older chassis. But you'll need to drill the captive nuts inside the crossmember to do this. This basic setup has proven to be very safe and durable over decades worth of competition use.

Is the vehicle to be used for competition at all?

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There should be crush tubes in the rear cross member anyway for when the tow bar is fitted, so a spreader as above on the inside (though I would go 5mm) and drill the nuts out and it will give you something really sturdy to pull on.

 

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Posted (edited)

Wow - could it be that simple?

 

I won't be using it for any form of competition. Unfortunately its in that awkward zone of use - whereby its a shiny, very well cared for 90 used for daily commuting that very occasionally would need need a heavy recovery from the rear (weekend safaris, morocco, etc.) Aiming for 2 or 3 major trips each year starting post COVID and I'll be travelling with people I don't know - so there's always a chance that someone will be a bit heavy-handed in a towed recovery. It if was more of a rough truck I'd be less bothered as I'd just fix it if anything moved/bent.

 

So, if on earlier models it was perfectly acceptable to attach a NATO hitch or Dixon Bate 5T pin directly to the rear crossmember (thinking Camel 110s here) - then a sufficient spreader plate coupled with some thick walled crush tubes (if required as per Bowie's point) and drilled out threads would effectively give me a similar effect? I'm conscious that the crossmember is made of thinner steel and that the bolt holes - at least in the upper mounts are of a smaller diameter than the lowers, which I'd like to rectify.

 

I'm having the work done for me on this one (no time or space with the 2x 2As I have on the go at home).

 

So... if I buy a recovery point, suitable nuts & bolts that will clear the tank and have a spreader plate laser cut then the only instructions I have to give to the garage (its an amazing place - that do old school, high quality work, the welding and fabrication they've done for me previously has been top notch) are as follows:

 

1) drill out captive threads

2) confirm that there's suitable crush tubes in situ, if not then break into crossmember and install 4x Xmm ID tubes (I'll supply the tube - have some thick walled stuff in stock).

3) weld-up, blast and paint.

4) on reassembly (before the tank is fitted) fit new recovery point with 5mm+ spreader plate on the back

 

Thinking about something like this - hoping the base is wide enough that a front spreader wouldn't be needed.

 

That changes things dramatically and would cost a lot less than the unnecessary NAS step I was planning to fit.

 

Thanks for your help on this guys - Uninformed - that looks like a hell of a thing! Trying to imagine how it'll fit. Dr Strangelove - I might give you a shout if that's OK when I've measured up and its time to get the DXF file: I've just got Fusion360 for exactly this sort of thing but have never used it before.

 

Edited by twodoorgaz
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I've used one of these. It's been on for 10 years, normal laning recoveries, no snatching. The crossmember seems to have withstood the strains put on it, most recently acting as an anchor for Ed Poore to winch his mud bound barge out.

HTH

Mo

 

20210625_081714.jpg

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1 hour ago, Mo Murphy said:

I've used one of these. It's been on for 10 years, normal laning recoveries, no snatching. The crossmember seems to have withstood the strains put on it, most recently acting as an anchor for Ed Poore to winch his mud bound barge out.

HTH

Mo

 

20210625_081714.jpg

Is that just bolted to the cross member using the captive nuts inside? If so, this is exactly the thing that was "deemed" unsafe for motorsport. We even spoke to Land Rover, whom confirmed that it is unsafe and not rated for recovery. The captive nuts have been welded, so are no longer high tensile. The cross member is prone to bending and bulging. And ultimately runs the risk of pulling through.

If it is bolted all the way through the crossmember with a spreader plate on the otherside, then none of the above applies.

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Well drumstick, I don't do any motorsport but the above has proved more than satisfactory for me for laning and I have no plans to change it. 

In the nicest possible way, I value my own experiences above others opinions.

Do you have a verifiable reference for your statement that Land Rover said it was unsafe ?

Mo

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1 hour ago, Mo Murphy said:

Well drumstick, I don't do any motorsport but the above has proved more than satisfactory for me for laning and I have no plans to change it. 

In the nicest possible way, I value my own experiences above others opinions.

Do you have a verifiable reference for your statement that Land Rover said it was unsafe ?

Mo

I don't have the comms myself. But it was a request made to Land Rover by the ALRC (Association of Land Rover Clubs). And we are regulated by the MSUK (Motorsport UK, aka MSA). It is documented in the ALRC EGM and SORC meeting minutes. And was a hot topic by the scrutineering team (that I'm a member of) for many months.

The result was the implementation of this regulation:

Screenshot 2021-06-25 at 11.14.13 am.png

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23 hours ago, twodoorgaz said:

 

 

…….Thanks for your help on this guys - Uninformed - that looks like a hell of a thing! Trying to imagine how it'll fit. 

 

I’m fabricating a new rear crossmember. These will bolt to the web (rear vertical face) right through with HD crush tubes ( LR version of crush tubes in the chassis are under done) 

 

 

607DE2CF-2D0D-478F-82F8-5C67E9ED881A.jpeg

F160D6F7-C487-491C-A9D2-688EFF77664C.jpeg

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21 minutes ago, Chicken Drumstick said:

I don't have the comms myself. But it was a request made to Land Rover by the ALRC (Association of Land Rover Clubs). And we are regulated by the MSUK (Motorsport UK, aka MSA). It is documented in the ALRC EGM and SORC meeting minutes. And was a hot topic by the scrutineering team (that I'm a member of) for many months.

The result was the implementation of this regulation:

Screenshot 2021-06-25 at 11.14.13 am.png

I'll stick with what I have as others I know have done also. I'm not motor sporting, use common sense in recovery and don't snatch recover but thanks for sharing. I believe the OP said he wasn't going to be doing motorsport either.

Mo

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I was always told not to use welded recovery points only one piece bolted ones with a spreader plate.

Mind you my bolted front tow hook (tow ball bolted horizontaly) is on a new Cross bar welded between the chassis legs.

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Posted (edited)
On 6/25/2021 at 11:32 AM, uninformed said:

I’m fabricating a new rear crossmember. These will bolt to the web (rear vertical face) right through with HD crush tubes ( LR version of crush tubes in the chassis are under done) 

Wow - they're going to be great!

 

OP here and think I'm now sorted thanks to your advice. Had a measure up and there seems to be 22mm of clearance between the tank and the rear crossmember.

 

With even a very thin spreader plate and a normal nut (whether M12, M14 or 1/2"UNF) this would leave virtually no gap before the tank - and those bits closest to the tank (the nut and tip of the bolt) would be pointy: not a nice thought in the event of a rear end collision and I'd like to leave a good amount (10mm) of space so that the tank can wobble without fretting against the bolts..

 

So, think I've decided on working from the inside out (obviously the tank'll be out when the chassis is being done) - that'll give me a bit more clearance (bolt heads are narrower than nuts, made better as it allows me to countersink them) and will give me a closer, but perfectly flat surface behind the tank, which feels like a safer option.

 

1) Cut access hole into crossmember and remove 4x upper M12 captive nuts, replace access flap with butt-welded steel, linish flat.

2) fit thick-walled crush tube behind the four holes of the crossmember (ID 15mm, 3mm wall - or nearest equivalent. Have a lathe so can make to suit) - coloured red on sketch. Also check all crossmember to chassis welds - add welds if any areas missed at the factory.

3) Galvanise

4) Order large spreader plate - most likely 10 or 12mm (way OTT, but gives lots of meat under every bit of the 7mm countersunk bolt head), drill 4x countersunk holes.

5) fit plate (coloured yellow on sketch) using 4x grade 8.8 countersunk M14 or 1/2UNF bolts (coloured blue on sketch) - length TBC

6) on rear, attach recovery point (design TBC, either a loop, swivel or pintle) with 4x nyloc grade 8.8 acorn/dome nuts (found these already - coloured green on sketch).

 

Job done. Its actually not that much effort, I can have the plate made at work and the garage will be fitting the tubes - the only downside is its a tank-out job if I ever want to change it, but I'm already in that position with the jate rings I have currently (these are hard to fit on a PUMA and even with the modified install sit very close to the tank - just a couple of mm at the closest point, not happy with these)..

 

It'll never be able to do crazy winch challenge snatch recoveries but even though the crossmember is apparently made from thinner steel when compared to a 300TDI I suspect the strength in a recovery situation won't be too far off, what with the large overly-thick spreader plate and crush tubes (not sure if a 300TDi had them). And that was good enough for the Camel Trophy.

 

Still making my mind up on the recovery point - just have to make sure the acorn nuts don't interfere or cause a snag hazard, but suppose that's only an issue if using a pintle like I've shown in the sketch where the rope could be in contact with them behind the pin, a recovery loop on a backplate wouldn't have that issue.

 

And no, I'm not doing any form of competition.

 

What do you think - seem like a sensible approach?

recovery point.jpg

Edited by twodoorgaz
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Posted (edited)

...The only other thing I've considered is adding a tack weld onto the heads of the bolts. That wouldn't stop me having to remove the tank if I ever wanted to take the assembly off, but it would mean I could change the recovery point for another design if the mood struck - as well as being able to tighten the nuts if they ever worked loose - the tank guard would prevent access, as would the tank itself as I couldn't get an Allen key into the gap.

Edited by twodoorgaz
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I wouldn’t worry so much about the tank clearance. Especially if it’s a diesel. 

The other option is captive nuts in the plate. Or if it’s a suitable grade and thick enough, drill and tap the plate instead. I’d feel happier with that than countersunk. 

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Thank you - I had thought of just using tapped holes in the spreader plate (an M14 full nut is 11mm thk vs the plate at 12mm), but have always been told that tapped holes are weaker than rolled threads in a true 8.8 (or 10.9) nut. In need of a bit of education: is there a grade of steel to look for in which a tapped hole would be comparable to a high-tensile nut?

 

I'd even considered thread inserts (Helicoils) or top hat bosses/barrel nuts 

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Class 8.8 are carbon steel

grade 8 or class 10.9 (and higher ) are equivalent to 4140

Rolled threads are definitely better than cut, and it use to be thought fine pitch stronger than coarse (larger root dia, more progressive torque) but the reality is, they can get more of a true radius in the valley or root of the coarse thread than the fine, hence the fine actually having a higher stress riser.

 

for high tensile bolts and a threaded hole in mild steel I’d like 1.5 times dia. In practice if you have equal material in nut and bolt, the nut height/length only has to be 0.65 times the bolt dia as long as there is one full thread (right around) protruding the back side of nut. 

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5 hours ago, landroversforever said:

I think a lot of stuff regarding finer pitch being stronger comes from stuff like a higher clamp load and a larger root diameter. Quite how the strength actually differs I’m not sure but its got to be better in shear.

In good practice, if a bolted joint is to be loaded in shear, there should be very little to no threaded section in the joint.  Definitely doesn’t happen in reality, but it’s why aircraft bolts come in 1/16 increments of grip length. I also try and buy bolts by grip length and cut off the excess thread. That’s why it’s better to stick with the genuine LR bolts under some circumstances as they are not what you can buy off the shelf as far as overall length vs grip length. 

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