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MG MGA - Stainless Steel Nts, Bolts & Screws

I am putting on a new top. The screws from the old rail were all totally rusted to the point of not doing much good. When I re-attach the rail I am thinking of using stainless steel screws. (Also thinking of them for other parts of the car as I replace things.) Is there a down side to using stainless?
(I am not concerned about concours condition.)
Thanks,
Steve
SJ Berg

Into the wood rail, I don't see a problem. Some disadvantages of stainless, are that it is generally softer than carbon steel, so a given stainless fastener may not be suitable in a given structural application. Also because it is softer, when threading stainless fasteners into carbon steel threads (or vice-versa), anti sieze lubricant should be used to prevent galling. Also, if stainless fasteners are used where they contact aluminum parts, a galvanic reaction can be set up which causes the aluminum to corrode.

Conventional wisdom is that stainless is harder than carbon steel, but conventional wisdom in this case is wrong. It only appears that way, because stainless work hardens, which can make cutting or bending it into an exercise in frustration.
Del Rawlins

To add to Del's comments, don't thread stainless into stainless, the two will almost always gall, even worse than stainless into carbon steel.
David DuBois

Hi Steve

Further to Dels comments, using stainless steel fastenings in areas prone to wetting etc can lead to accelerated corrosion of the surrounding mild steel also due to galvanic action.

In this application, better to use zinc plated bolts. (unless you never drive in the wet of course)

Cheers
Ian F



Ian Fraser

Greetings:

I've always used fasteners in the following order:

1. grade 8 (alloy, plated, tempered)
2. grade 5 (alloy, plated, tempered)
3. stainless (alloy, no plating)
4. cad plated carbon steel (gray-ish plated)
5. zinc plated carbon steel (blue-ish plated)

I chose in this order when originality was not at stake (hidden fasteners e.g. floorboards, etc.). Usually grade 8 & 5 are for load bearing applications (suspension, etc.) Most of the fasteners I've used have come from Todd Clarke and most of them appear to be cad plated, but I've seen several parts from Moss, etc. (heater valve, heater box spring clamps, e.g.) in the yellow-ish plating which is probably a less expensive relative of zinc. Original BMC data shows all fasteners being plain, zinc or chromium (really, chromium?). Based on my experiences with these platings, I think what BMC supplied may be different than what's available today.

Ten years after my restoration, I'm seeing that my picks (see list above) were basically sound because most of the rust and other nasty stuff has happened toward the bottom of the list and the top of the list is holding up pretty well.

Can any of you engineers refer us to a resource where a material or plating choice can be made based on resistance to weather? Can you help straighten me out as to what BMC originally supplied (what is "plain" and how do you spot it, and how do you spot chromium plating?). Barney's site is great, but I don't see this type of information listed.

I'm probably mislead - please straighten me out.

Thanks

Gary Hattwick
Gary

Hi Ian,
I intended to put my floorboards back using stainless fasteners. Not a good idea then?
Cheers
Tony
Tony

Hi Tony

Electrolysis is a bit like gravity - you can put it off for a while, but it will always win eventually.

There are surface treatments available for SS fastenings, and you can spread all sorts of other coatings on both the body parts and the fastenings that will delay the onset of corrosion for perhaps the lifetime of the rest of the vehicle, but if there is a 'holiday' in the protection system, corrosion of the mild steel will start near the fastening.

A quite common example of this type of electolysis is the corosion that takes place in the vicinity of the swivel pin (often SS) on the backing strip arrangement that holds replaceable windscreen wiper blades. Both my Toyota ute and out recently departed Mazda Capella suffered from this, and I have seen it on other vehicles.

For your floor boards? Well my choice would be to go for zinc plated steel screws in conjunction with lanolin or fish oil, the problem is the quality of the plating. Some manufacturers have managed to make a coating of a couple of atoms thick look like the real thing. See if you can get some with a 'proper' coating. Another way is to get the screws plated by an electroplater, then you will know what you have got.

Cheers
Ian F



Ian Fraser

I used stainless steel fasteners to put the body of my pickup truck back together about 5-6 years ago, and have had no problems to date (truck sits out in the weather). I was very careful to apply anti sieze coating wherever stainless threaded into carbon steel. Corrosion is more of a problem between stainless and aluminum because they are farther apart on the galvanic chart than stainless and carbon steels. Problems are commonly seen on light aircraft, where owners replace plated carbon steel screws holding panels, etc. in place with stainless screws. They even sell kits for this purpose. Problem being, that the aluminum structure becomes the anode in the galvanic relationship, and corrodes away around the stainless fasteners. The original type carbon steel fasteners are plated with a sacrificial metal (on aircraft, usually cadmium) which eventually corrodes away. They would be better off just buying new fasteners every few years as the plating is used up.

Hardware store bolts these days are generally zinc plated, regardless of their grade or color, which is added in a different process in the case of the golden yellow colored (usually grade 8) fasteners. Due to the toxicity of cadmium plating when heated or welded manufacturers have pretty much switched to zinc out of liability concerns. Zinc will make you sick for a while, but it doesn't do permanent damage like cad will. Cadmium is still heavily used in the aircraft industry, however, so avoid welding on or torch heating any AN or MS standard fasteners you may have around.
Del Rawlins

Hey guys:

I don't mean to belabor this thing but zinc plated anything rusts!! The stuff you buy at the hardware store that is zinc plated will rust. I'm living this experience every day. It's the first of the platings to deteriorate. BMC fastener charts show zinc as one of three original finishes, but I have not found a zinc plated fastener that won't rust. Ian: what kind have you found that don't rust? I may be shopping in the wrong stores, but (IMHO) cad holds up better with ss being better yet. This is regardless of hardness which is another issue altogether.

The points made about coating with fish oil or another material is great if you can maintain that coating - personally, I don't crawl under often enough to inspect and "top up" applied coatings.

Del's point about galvanic action causing corrosion is undoubtedly correct, so I'd avoid a ferrous metal against aluminum, no question. I have not had any issues with shiny chrome plated connectors against unplated ferrous metals, but I am seeing corrosion (not rust) between cad and stainless in exposed applications.

To answer Steve's question about the header rails: My suggestion (FWIW) is cad plated or ss hardware. Since you're screwing into a painted frame, metal to metal contact should be minimized and your assembly should last a good long time.

To answer Tony's question about floorboards: SS should work fine. I used stainless nyloc nuts with stainless flat washers and screws but I used cad plated finishing washers inside (couldn't find ss)- 10 years so far with minimal corrosion at the screw head/finishing washer boundry. SS everything should be excellent. Since you're up against paint, galvanic action should not be a factor. Note: it's not original, but no one has looked under my carpets yet.

I think we need the guru to chime in here.

Best of luck,

Gary Hattwick
Gary

IMHO I don't thing using stainless fasteners for the floor boards is a good idea. I'm sure that your car will be well maintained and not subject to many outings in poor weather, but given the corrosion possibility of any fastener and the difficulity in removing a stainless bolt if siezed (harder to drill out) I'd stay with conventional zinc plated fasteners in that area. Since this is not a 'high stress' area, perhaps bronze bolts would serve the purpose and provide resistance to corrosion. Seem to work for the boating crowd.
Bill Young

The biggest problem with the floorboard area is damp carpets.
If you are careful not to leave damp carpets covering this area just about any fastener will perform just fine with minimal corrosion.
This is great for garage queens but cars that are driven daily in a wet climate or stored outdoors are more difficult to keep dry.

BTW: My plater calls the gold coloured plating "Cad II"

Cheers,
Rich
Rich McKIe

It is my understanding, that the gold color comes from a conversion coating done prior to plating, and can be present with both cad or zinc plating. In my work on aircraft I am seeing more new fasteners that are silver in color, instead of gold, but they are still cad plated. This caused some concern at first, and inquiries were made, but word came down from above that the new bolts were correct.

I've been thinking of ordering one of these tin plating kits for restoring fasteners for my car:

http://www.caswellplating.com/kits/tin_plate.htm

The main appeal of the tin plating kit is that since it is non hazmat, I should be able to get it shipped to Alaska. Everything short of massive shipments generally comes here by air.
Del Rawlins

Hi gary

Essentially the problem as I see it is that with any fastening or metal to metal connection involving different metals galvanic corrosion will take place if the area is wet (or subject to wetness) and there is a loss of insulating coating on both metals surrounding the area where metal to metal contact occurs.

If two pieces of steel are fastened to gether with a SS bolt, you can almost be certain that there will be metal to metal contact between the bolt and the steel within the fastening somewhere.

If there is no protective coating on the steel and bolt close to the fastening, in wet conditions a galvanic cell will be set up and the mild steel will be subject to corrosion.

If in the same joint a plated steel bolt is used, under the same conditions the plating of the bolt will be sacrificed rather than the parent steel. Eventually however the plating will be all gone and rusting of the parent metal and the bolt will take place, but there is a period where thae sacrificial plating will protect both bolt and parent metal.

Choosing between SS and plated bolts comes down to - sacrifice the car or the bolt?

Even if all steel parts are protected by a properly applied paint system, it is inevitable that some damage to the paint system will occur when the bolt is tightened up, and some flexible and penetrative sealer can be used to advantage. There are various products, I use fish oil because I have it in a spray can, it penetrates well, and it dries to a jelly like state that adheres well to the joint.


Cheers
Ian F

Ian Fraser

Hi Guys
Thanks for all the responses, I guess I have around six months to ponder which way to go - at present work rate.

To come really clean on my idea, I had decided to use 20mm long SS M6 countersunk socket head screws with lock nuts on the underside. I have made a small die to produce SS shaped washers for the inside, made from standard large flat 6mm washers.

I know the above will offend the purist but 1/4 unf SS screws are very difficult & expensive to obtain. Whereas M6 SS screws are "tuppence a bucketful" and the compatibility in terms of thread form is close - hence the use of locknuts + it covers all those ugly long exposed screws. And removing all those socket heads with a cordless driver is a doddle.

Thanks again
Tony
Tony Mitchell

Hi Dell

Tin is pretty good at protecting steel as long as the coating remains intact, it similar to aluminium, chrome, (and stainless steel) in that it forms a thin oxide layer on its surface that protects it from further oxidation.

Sadly however, if the coating is breached, the underlying steel will corrode at the expense of the tin.

IMHO you would be better uing a zinc plating kit.

Cheers
Ian F

Ian Fraser

1/4-28 flat head Stainless screws are available.
Start here: http://www.mcmaster.com
Under Fastening and Sealing Click on "Machine Screws".
Then start clicking on:
Socket Head Cap Screws
Flat head
Hex Socket
Stainless steel
1/4-28
18-8 material is fine for floorboards.
Then pick the length you want.
1 inch long is $9.04 pre pack of 25.

They also have countersunk finishing washers in stainless steel for $5.63/100

Not only does McMaster Carr have nearly any fastener available, but they sell to anyone, no minimum order, and shipping is reasonable price. I also buy welding supplies there, and lots of other things.
Barney Gaylord

Thanks, that tells me what I need to know. It may be possible for me to get a zinc kit shipped up by barge, or by somebody driving up through Canada later this year, but it adds another level of complication since it will have to change hands once or twice extra. It's the downside of living in paradise.
Del Rawlins

Ian:

I completely agree with your suggestion that paint stinks as an insulator! I also agree that there will always be galvanic action especially when there's an efficient conductor like water present (physics, doncha love it?).

It sounds like we're fighting a battle that can be won, however and your fish oil may help delay the inevitable for the hidden fasteners. I know I've seen it refered to elsewhere on this bb, but does anyone remember a US source for this wonderful stuff?

The visible fasteners will just need to be replaced periodically.

Sounds like I need to crawl under and try to save my stainless, cad and zinc fasteners before they all go away.

Thanks to everyone,

Gary Hattwick
Gary

Another look shows that I may have had their zinc kits confused with the nickel kits, so I should be able to get it shipped here through normal means. Now I just have to decide if it is worth bothering with, instead of sending those fasteners and parts for which original style replacements are no longer available to a plating shop.
Del Rawlins

Hi Barney I have to disagree with your statement that "McMaster Carr sells to anyone." I tried purchasing some threaded inserts from them, and after receiving an email shipping confirmation from them, waited patiently. After a month of waiting, and having received no parts, I contacted McMaster Carr and was subsequently informed that they "do not sell to Canadian customers!" Needless to say that I was not very happy with McMaster Carr, or their treatment of this potential repeat customer! Cheers, Glenn
Glenn

Thanks to all. Silly me assumed stainless would be the way to go because it doesn't rust but now I realize that using it may encourage the metals around it to rust faster than otherwise.
I too have purchased from McMaster and they are great!
Steve
SJ Berg

Just a note on plating. All plating is not equal. Zinc plating is either hot dipped or electroplated. Electroplating is beautiful and shiny, but it is the plating that is an atom or two thick. If you would like some permanence in your plating, go for hot dipped.
mike parker

This thread was discussed between 08/01/2007 and 11/01/2007

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