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MG Midget and Sprite Technical - Door striker back plates in Ti?

The steel backplates for the striker are either a 1 piece item (weight not known) or 2 pieces with a combined weight of 207g x 2 = weight on car of 414g.

The thickness is 6.43mm/1/4".

I'm guessing there is no great science to the choice of thickness and that the plate is over engineered since the metal thickness of the B post would fail long before the plate or maybe the 3 screws would. Does anyone disagree and if so why?

So, is there any reason why it's a bad idea to replace the 6.43mm steel plate with 4mm Titanium plate?
Daniel Stapleton

unless you use a thicker shim you'll have to adjust the door fit and will have a bigger door gap when closed.
David Smith

I would question why you are using titanium? when aluminum is cheaper, more readily available, lighter and using a grade such as 6082-T6 is still as strong as "cheapo" mild steel.

Although struggling to visualise what part you are on about...?!

Malcolm

If you are that obsessed with weight saving there has got to be easier ways surely?!
M Le Chevalier

ooo... the bits with the threads in that go inside the door post?

Go ali. with coarse threads and get some new bolts?

Or, I lost one of mine, I made up a new one using the one from the other side as a template by just welding a couple of half nuts onto some thin steel.

I figure the "plate" doesn't really serve a purpose other than to make sure the holes are in the right alignment.

Malcolm
M Le Chevalier

David,

I thought Daniel was meaning the plated steel plates that act as fixings for the striker plate - these fit into hidden pockets in the B post and only act as fixed nuts - so how is the door fit altered ?

My concern would be reduction in the thickness for threading i.e less than 80% of bolt dia (as a fixed nut).

R.
richard boobier

I would not use nuts on a thin plate as the plate acts to spread loading to avoid pulling through the thin B post in the event of an accident.

R.
richard boobier

I replaced the stupidly heavy blocks on mine a few years ago. Mine were the two piece ones and of a similar weight to what Daniel states. I replaced them with 16swg 7075-T3 ally with aircraft style floating anchor nuts and solid rivets to attach them.

The old plates slide out of the slot on the B pillar and the new plates just slide in to replace them. I can't remember what they weighed but it was a tiny fraction of the steel plates.

I know it sounds a bit OTT to go to those lengths but when you have paid hundreds of pounds to save the odd Kg on things like lighter alternators, starter motor etc, saving about a third of a kg for free is fantastic! Plus if you couple it with all the other cost free little mods they all add up to a significant weight loss. For example I removed the recesses for the bonnet hinges which saved about the same as the B post plates. My favourite is the removing of the steering column shroud by making an oilite bush holder for the top mount (see pic).

Anyway in answer to Daniels question I would say that there is no problem replacing the plates but if you are doing it you might as well make your replacements as light as possible.

john payne

Mmm, yes 4mm not much for the fastners to bite on.

Yes, these are the bits the other side of the B post.

The bolts are in fact countersunk posidrive so might not readily be available in UNC.

Thin plates and welded bolts might be ok - I suppose it depends how thin the plate is.

So, I'm in favour of alloy plate of which I have some scrap in my garage I can use.

John, can you advise me what 16swg is in mm or thou so I can near match to one of the two thicknesses of scrap plate I have or buy to suit. Also do you have a photo of how you did this (how do the plates slide out with the anchor nuts on them)?

Why bother? As John states every bit of weight saved adds up so the grams become Kg and the Kg become tens of Kg and modern cars disappear in the rear mirror. Also, it gets harder and more expensive to save weight as the car gets more developed so these small savings are useful wins.

Photo attached of my lightened striker plate - the one in the middle (I have a spare set for sale....) that was expensive to get re-plated.



Daniel Stapleton

16swg is easy to remember, as it is 1.6mm and 1/16" (don't ask me for any other swg equivalents).

As an alternative, could you just lighten the 4mm steel by drilling where the 'meat' is not needed?
Jonathan Severn

Although these days you would be lucky to see true 16swg in steel, IIRC it is 0.065" so very close to 1.6mm and 1/16". In the change to metric the standard equivalent to 16swg is 1.5mm but with the cost of metal the mills seem to be pushing what they can get away with and I have seen some 1.5mm as low as 1.3mm, it makes a difference in some circumstances. I think my local stockist has non ferrous such as brass and copper still in the swg sizes but haven't checked the accuracy recently.
David Billington

Just RE: countersunk UNC bolts: search ebay, loads of 'em. Are they 5/16"? I can't remember, but one such example:

http://www.ebay.co.uk/itm/5-16-UNC-SOCKET-COUNTERSUNK-ALLEN-SCREW-BOLTS-10-PACK-/130913896841?pt=UK_DIY_Material_Nails_Fixing_MJ&var=&hash=item1e7b138989

Malcolm
M Le Chevalier

Sorry Daniel, didn't take any photos. But a quiet day at work today so I've made an example!

I was wrong about the ally I used, it was 7075-T6 not T3, a minor point though!!

The one I've made today is 3" x 3" as I can't remember the original size. It is 1.6 mm thick or 0.063".

Here is a pic of the anchor nut (hardened steel floating type and a UNF thread) which is 3/16 as I couldn't lay my hands on a 5/16 one. Also the two 3/32 solid rivets to attach it the plate:

john payne

Here is the plate drilled off and with one position countersunk for the rivets:

john payne

The finished article with the two anchor nuts riveted in place:

john payne

Here it is on the scales. Obviously not exact as the original are going to be a different size but I seem to remember all the 4 plates coming in at less than 100g.

Strength wise I don't think it's an issue. I can't imagine many situations when you are going to get a pulling force on that part, only really in shear and the screws are going to take all that as normal.

I also did a similar job to Daniel's on the striker plates.

john payne

Just a thought John; the plates get pulled up against the inner side of the B pillar, yes? I would've thought the initial shear resistance would be friction as the plate floats. If you have rivet heads or tails protruding does that not reduce it, maybe to an amount where it's too easy for the plate to move when you don't want it to?
David Smith

David, the plate sits totally flush due to the countersunk rivets. It's the same principle as just about every removable panel on most aircraft. The rivets in the anchor nuts are only there to stop them turning and to 'anchor' them, they don't really have any structural use. In fact some anchor nuts are held on by hollow 'pop' rivets. The only sideways movement will be what is allowed by the oversize holes in the B pillar which would be there with the original plate.

They haven't moved in the 3 years since setting the doors up and I wouldn't expect them to as it's just the same as original, just a lot lighter.
john payne

countersunk rivets? sound cool, new to me, must remember to take a look in my local fasteners shop...
David Smith

Hi John,

Do you want to make 3 more and sell/trade them with me?
Daniel Stapleton

I'll have a go Daniel. I think I may still have the old plates somewhere so should be able to use them as a template. If I can't find them you could either send me the dimensions of yours or send me the plates.

I'll let you know after I've rummaged through my garage later.

john payne

Fond the plates Daniel. I'll try and get them done in the next couple of weeks.
john payne

I thought the idea of counter sunk rivits was interesting also...my eyes are wide open as well

=-O

Prop
Prop and the Blackhole Midget

This thread was discussed between 20/02/2014 and 22/02/2014

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