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Gasket

Member Since: 30 May 2020
Location: Manchester
Posts: 629

Crossmember captive nuts and clearance for spreader plate?

Hi folks.

In a few weeks the Puma is going tin to have its chassis stripped and galvanised. While there there is an opportunity to effect some simple mods to address known issues.

One thing I'm seriously looking into is the captive nuts on the rear crossmember. I need to get to the Defender to check (iI'm not at home at the moment) - but I believe that on a 90 there is sufficient clearance between the crossmember and fuel tank to fit a large spreader plate and four nuts. If that's correct then I would be very tempted to have some minor surgery done to the crossmember:

Break into the crossmember and remove the captive nuts/nutserts. Replace with thick-walled crush tubes passing straight through the crossmember, invisibly weld it all up, galv and respray.

Of course if I did nothing I’d have to have the threads retapped anyway due to the buildup of zinc when galvanising so replacing with a straight tube avoids this to a degree (if there’s space for the nut heads).

If that would work then I could in fact mount a simple recovery point directly to the crossmember (for all but snatch recoveries noting how thin the steel of the crossmember is on these things) with a 5-10mm backing plate behind. 4x 8.8 bolts passed straight through.

Does anyone happen to know whether there are already crush tubes in any of the four holes? Also, could anyone advise what the captive nuts look like - plates or flanged nuts/attached to back wall or front wall/etc?

29th Jun 2021 12:57pm

Dinnu

Member Since: 24 Dec 2019
Location: Lija
Posts: 3409

2012 Defender 90 Puma 2.2 CSW Santorini Black

I can possibly answer your last question (I opened up one rear cross member from Td5, which is same as Puma).

There are no anti crush tubes.

If I remember correctly, the captive nuts are square nuts welded internally (probably more tack welded). These are welded to what is like a spreader plate, about 5" to 6" wide, and not to the external skin of the cross member. This 'spreader plate is welded to a smaller internal channel, which can be partially be seen through the squarish hole. The skin of the cross member is a U channel that is welded at the top and bottom of the smaller channel. 1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing
2012 90 CSW, 2.2TDCI, Santorini Black

29th Jun 2021 1:12pm

blackwolf

Member Since: 03 Nov 2009
Location: South West England
Posts: 17344

2007 Defender 110 Puma 2.4 DCPU Stornoway Grey

If you haven't already done so, take a look at the pictures on the second page of this thread. They will answer many of your questions.

29th Jun 2021 2:01pm

Gasket

Member Since: 30 May 2020
Location: Manchester
Posts: 629

H both - that's really helpful, thank you! I hadn't found that thread in my search.

29th Jun 2021 6:01pm

Gasket

Member Since: 30 May 2020
Location: Manchester
Posts: 629

Ah… bit of an issue.

Have just got back home, earlier than planned, and couldn’t wait. Armed with a torch ive just been under the back of the 90. It’s difficult to measure accurately with the tank support plate in place but the distance from the back of the crossmember to the plastic fuel tank is just over 20mm.

Now the issue is fitting a nut into that gap: a full-sized nylon m16 nut (type p) is 18mm thick. A thin m16 nut is 16mm thick. Add a little extr for a thread or two sticking through and you’re up to 17.5mm or 19.5mm.

Then you need the spreader of between 5 and 10mm.

And you need a sensible clearance before the tank to allow for vibration.

I don’t think it can work unless I had a recessed plate welded in effectively replacing the back wall of the crossmember.

.

The only thing I can think of is to make the spreader plate from 5mm steel. Then pass the bolts from the inside of the crossember to the outside - through the crush tubes, with the nuts on the outside of the vehicle. I could tack the bolt heads to the spreader plate so the whole assembly (4x bolts and spreader plate) passed through the crossmember in one hit.

As a m16 bolt head is only 10mm thick… add a 5mm plate and that’s 15mm - leaving 5/6mm before the tank but it’d look a bit odd and there wouldn’t be much clearance at all.

Think I’m going to end up with a whole NAS step just to get a recovery point here.

29th Jun 2021 11:11pm

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