Which grade bolts do I need?

Body parts, seats, dash, headlining, windows and stuff!

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Alan_M
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Which grade bolts do I need?

Post by Alan_M »

I’ve had to cut the bolts holding the seats in as so badly rusted. Also I will be drilling out the set screws that hold the door latch striker plate onto the body as heads have been mullered by PO.

For the seats I was thinking off using stainless Allen headed bolts (M8x40mm) to both allow easier removal in the future from rust point of view, and also to avoid the issue of not being able to get a socket or spanner on the bolt head in the seat runner to stop it turning.
These appear to be available in A2, A4 and A4-80 grades - what would the minimum grade that would be suitable?

For the striker plate Allen headed setscrews (M6x45mm), I was thinking of changing to torx headed ones which I’ve found in a choice of A2 or A4 stainless.

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Re: Which grade bolts do I need?

Post by Pete Boole »

Stainless is significantly weaker than than the bolts you have taken out, either A2 or A4. I wouldn't use stainless in any situation where strength is vital - OK for other bits though. If you want to make the seats easier to remove later just use zinc-plated socket cap heads - they are usually 12.9 grade - the runners will break before the bolts! So long as you use plenty of copperslip on assembly they will be fine, and you can get a hex bit on them easily. Same advice for the striker plate really - it's part of the safety of the door beam assembly. I've been trying to find some countersunk Torx heads as well, but they are hard to find, so I may end up using hex-drives again.

Pete

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Re: Which grade bolts do I need?

Post by MetBlue »

When drilling out the striker screws, if you use a drill between 5 and 6 mm, you will only need to drill the c'sunk head off each screw. All being well, the nut plate with both screw threads in can then be just pulled out from inside the rear quarter panel. The holes in the Ali block are 8 mm, so you'll be very unlucky if the striker bolts are seized into the Ali.
Once the nut plate is out, it shouldn't be a problem to free the rest of the screw.
Tony
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Re: Which grade bolts do I need?

Post by rbgosling »

While stainless is (typically) weaker, I'd still say it's more than strong enough for the seat bolts. I've just bought replacements for mine as the seats are out as part of the re-covering job, allen-headed same as you are considering. Honestly, I would be happy using stainless for more or less anything outside of engine/driveline or suspension/brakes etc. I'm more than sufficiently fed up of rusty bolts.

It is important to think how the bolt will be holding the load. In some cases (admittedly including the seats in a crash situation) the bolts will be loaded in tension. In many others, the bolt will be holding together two surfaces that will be trying to slide against each other. In these cases, if the joint is properly designed, it should be friction between the surfaces that carries the load, not shear of the bolt itself. The bolt simply needs to press the surfaces tight enough together to generate sufficient friction, and further tension or strength achieves nothing.
"Farmer" Richard

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Alan_M
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Re: Which grade bolts do I need?

Post by Alan_M »

Thanks guys.

Richard, with your background, I’m happy to take your advice :D Also thinking about it a bit more I would suspect that the first thing to go will be the bolt being pulled through the fibreglass floor before the bolt would shear, even stainless. Which grade stainless are you using?

I’ve also now seen a BO, unbrako 12.9 socket head bolt that are black - anyone know what the corrosion resistance is like on these compared with BZP? If these are more corrosion resistant, then they may be a good option.

Peter - For the striker, I think I will go with BZP-10.9 as thinking about these, during a side impact into the door beam they will be under both tension and shear.

Tony - thanks, that is what I was planning on doing.

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Re: Which grade bolts do I need?

Post by Pete Boole »

"self-coloured" black bolts last about 1/2 hour before going rusty! They are for use in engines etc.. where they don't need corrosion protection.

Pete

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Re: Which grade bolts do I need?

Post by CID »

Hello Alan,

Yes 12.9 will be more then enough. The black ones are mostly chemically blackened. Not so protective as plated.
But after mounting the new bolts spray some bitumen to cover the whole thing. Will be enough.

Do not forget to use a slightly bigger washer on the bottom side and apply some sealer around it to make it water prove... Some IP67 like :lol:

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Re: Which grade bolts do I need?

Post by Sirclip »

I would imagine that the main 'safety critical' component is actually the safety belts and their mounting bolts, rather than the seat bolts themsleves.

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Re: Which grade bolts do I need?

Post by DavidOliver »

The strength of seat runner bolts IMO is not critical. In a front end crash the body leaves the seat behind, the safety belts take the load
and in the Excel, front belts are anchored laterally, no shear, and backseat by a large external plate. In a crash from behind the two front
runner bolts will try and rip out of the fibreglass, so use very large and thick washers on the underside. Our seats have a good headrest to stop
whiplash and it might be preferable to allow the seat to rotate backwards. We also have crushable rear body and spare wheel to cushion a rear shock.

On bolts, I like the Jag bolts with very sturdy hex heads, zinced, incorporated washer and fine thread for greater load application.

Here´s a pic I hope, new found toy!




Image

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MetBlue
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Re: Which grade bolts do I need?

Post by MetBlue »

Here´s a pic I hope, new found toy!
Me thinks you need a bit more practice with you new toy. I think you've pasted it AFTER the second [ not before.
Tony
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Re: Which grade bolts do I need?

Post by DavidOliver »

Image

Photograph of Jag type bolt.


Has this worked?
Dave the cog.

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MetBlue
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Re: Which grade bolts do I need?

Post by MetBlue »

That's better. Easy once you've done it a couple of times. :D :D
Tony
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Alan_M
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Re: Which grade bolts do I need?

Post by Alan_M »

Pete Boole wrote:
Sat May 23, 2020 19:57
"self-coloured" black bolts last about 1/2 hour before going rusty! They are for use in engines etc.. where they don't need corrosion protection.

Pete
Thanks - I will avoid those then.

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Alan_M
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Re: Which grade bolts do I need?

Post by Alan_M »

CID wrote:
Sat May 23, 2020 20:01
Hello Alan,

Yes 12.9 will be more then enough. The black ones are mostly chemically blackened. Not so protective as plated.
But after mounting the new bolts spray some bitumen to cover the whole thing. Will be enough.

Do not forget to use a slightly bigger washer on the bottom side and apply some sealer around it to make it water prove... Some IP67 like :lol:
Cheers - I will be using some nice big penny washers and spraying with underseal .

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Alan_M
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Re: Which grade bolts do I need?

Post by Alan_M »

Sirclip wrote:
Sun May 24, 2020 18:53
I would imagine that the main 'safety critical' component is actually the safety belts and their mounting bolts, rather than the seat bolts themsleves.
DavidOliver wrote:
Mon May 25, 2020 10:53
The strength of seat runner bolts IMO is not critical. In a front end crash the body leaves the seat behind, the safety belts take the load
and in the Excel, front belts are anchored laterally, no shear, and backseat by a large external plate. In a crash from behind the two front
runner bolts will try and rip out of the fibreglass, so use very large and thick washers on the underside. Our seats have a good headrest to stop
whiplash and it might be preferable to allow the seat to rotate backwards. We also have crushable rear body and spare wheel to cushion a rear shock.


On bolts, I like the Jag bolts with very sturdy hex heads, zinced, incorporated washer and fine thread for greater load application.

Here´s a pic I hope, new found toy!

All sounds very logical.

As to JAG bolts, I’m trying to stay away from hex head type as you can’t get a socket onto the bolts in the runners to stop them turning so end up trying to wedge them with a screw driver. Ideally, I would like to find a source of flanged hexalobular bolts, but they are hard to find. Hence the reason for probably going for a torx or Allen headed bolt.

Ps Dave, congrats on your new picture posting skill :D

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