Plating and restrengthening suspension bolts

[Flat 6]

Hey all,

I'm refurbishing my suspension and was planning on getting all the fixings and some other parts yellow/gold plated as per some of the resto threads on here.

I note from Jamie's thread that the metal is made brittle by plating and needs to be heated again to 200°c to return original strength properties (can't quite recall the proper engineering/materials - is it tempering? ).

I am weighing up my preference for using original parts with buying new fixings which I did for my SC resto. Few of my new fixings came from Porsche with the yellow/gold finish, most were grey or silver. Don't think bolts are galvanised are they?

I haven't spoken to the plater I will be using about post-plating heat treatment but presumably they will be very familiar with this requirement. Is it something I can do in a home oven or should I trust them to do it?

Cheers!

Al.

[Bruce M]

Hydrogen embrittlement

Check the plater know about it. Don’t assume.

[inaglasshouse]

Hydrogen embrittlement

Check the plater know about it. Don’t assume.

Indeed...

Also please note that, to avoid embrittlement, the "baking" needs to be done immediately after the hydrogen exposure (the plating). So your plater needs to do it, it can't wait until later.

It's only higher strength steels that really suffer, but you are talking about suspension where some of the bolts are 10.9 and most are 8.8, so they definitely need baking after plating.

[911hillclimber]

All above so true
They will fail under load, and mine failed 24 hours after torquing tight, all pro plated too.
IMHO just buy new ones, nobody will see the heads to check!

[Flat 6]

Thanks all, definitely need to get this right, hence the post.

I'm leaning towards new. Presumably I can specify yellow passivated bolts specifically for 'structural' areas like suspension and drivetrain?

What have others done?

I'm hoping to achieve the same top end look as many of the superb looking restorations on here. Been through most of them in recent weeks and they all have the yellow passivated look. Hope Bigfoot doesn't mind me using his photo as an example...



If any of you guys are tuned in, did you replate or buy new? As I said above, stuff I bought from my OPC for the SC wasn't generally yellow passivated so maybe I need to hunt elsewhere?

Al

[Guy]

I had read about the possible embrittlement so have used new from Porsche for my Carrera 2.7 restoration. I would say most have come with the original yellow passivate finish but a lot have not.

If you want the original look the sizes are listed in the parts catalogues and you can then search for the size with the yellow zinc finish.

I haven't ordered from here but seems to have original yellow zinc finish bolts, etc and also references the Porsche part number from the catalogue.

https://www.ebay.de/str/missing-parts-d ... 7675.l2563

Postage seems high but would be fine if he does combined postage for multiple items.

[911hillclimber]

The yellow colour comes from using Chrome 6 in the plating, known as Yellow Passivation.
The 'silver' finish is the modern plating without the use of chrome which is a very polluting heavy metal and generally has been banned by many countries a long time ago, hence the fasteners from Porsche are prob pre and post this legislation.

I know many find platers who will do the chrome passivation (yellow) finish, but most fastener suppliers only sell clear pass finish.

I have used a company called Namrick for decades on all my 2 and 4 wheel projects, all high tensile, all clear (silver) finish, and NEVER had a failure ever.

Suspension integrity is crucial of course, but all fastenings are, hence I simply use new clear pass. though accept the yellow finish is very period.
You need to find a good plater who works to correct standards, but I had a bad experience when I/ had cap head bolts for my hotrod suspension plated and every one broke because of hydrogen embrittlement.
You normally cannot buy plated cap heads for good reason. High tensile bolts have a high carbon content and that is where things can go wrong.

Since then I simple used new and have no worries.

[Flat 6]

Thanks all,

I have looked at the heads of the bucket of bolts I was going to get plated and they all look to be 8.8.

There seem to be plenty of eBay suppliers offering yellow passivated 8.8 and even 10.9 so I’m thinking it’s not really worth taking the risk with getting stuff replated.

Now for some fun evenings measuring and ordering bolts...

Al.

[Cookie]

I looked into this at length. I read an article which said failures will occur in the first 24 hours or so as someone has already said. I use new bolts mostly but zinc yellow is getting harder to find.

[911hillclimber]

Yes, that is typical of hydrogen embrittlement, failure within 24 hours after tightening.
However, how would you know it had failed?
A crack can be there and the fastener looks fine, ultimate failure is when you least want it....60mph into a 90 deg left lets say.

My experience was with cap head screws, M12, nyloc nuts.
Used them on the front suspension of a hot rod I was building (Model A Ford, V8 etc) and all the bolts were exposed.
Day after fitting found 6 of the 8 had lost their heads on the garage floor, 2 a long way away from the car, so failure could have been a real shock failure, and the other 2 came off in my hand when I touched them, but they looked intact.

Why risk any of this when you can buy good clear plated fasteners in any size you need?

[911FVD]

Wish someone would explain to the Chinese fastener companies about hydrogen embrittlement as the number of times now the heads break of self tappers when screwing up has lead me now to just throw them and most often now I buy stainless steel from a UK supplier. For some technical reason and I know not why the weakest and most concentrated area ends up at the kneck of the bolts or screws. I have had them break off even before fully torqued up.
My car was rebuilt totally with all new fastenings (Porsche supplied) and the only items replated were the odd part those that either could not be found available or brackets that the cost of new was horrendous against the cost of plating.
I do a lot of classic cars and for many parts I have to get plated as unavailable and have my own small plating set up and can do yellow too but I never bother with bolts, nuts or springs. I also have a little mini caravan oven I can bake them if considered 'at risk'

Steve

[Flat 6]

Thanks Steve,

Where did you get your bolts for your spring plates?

Al

[deano]

I tried so hard not to let the materials scientist in me wade in

I'm not an expert on H embrittement, but a couple of interesting and hopefully helpful figures came out of my short analysis.

Yes, plated parts absorb H
Yes, H causes emb, but only when under mechanical stress (not in storage), therefore:
Yes, if your bolts have microfractures, which they might well have especially if used, they could fail under load
Yes, you can bake them at home at 190 C, and you might want to, even if the plater did so, because:

Look at the baking times versus stress capability curve on Wiki: https://en.wikipedia.org/wiki/Hydrogen_ ... ent#Steels

An 8.8 bolts have a yield strength of about 850 MPa (N/m^2) - Google search tensile or yield strength values
- the curve shows that you need a 7 hour bake (the horizontal flat line denotes no failures at that stress value)

A 10.9 bolt needs something like 10 hours (1000 MPa)

Consider these questions though:

- Did your plater bake for at least those periods?
- Did the manufacturer of your shiny new plated Ebay bolts?
- How about those that you purchased from Porsche?

[911FVD]

Hi,

Flat6 all the body, chassis and trim final assembly new parts came from Porsche Centre Colchester.
The engine gearbox and brakes etc were all stripped and sent to CTR Racing. The PO who had all the work done appears to have had some special relationship as I have no documents or invoices for this work other than the pictures when everything was returned 6 months later with everything looking as new. The whole final assembly has over 200 pictures showing everything part by part being assembled and masses of invoices for the parts. Although the labour was done by Chaplane (then a Porsche approved body specialist) the PO appears to have purchased all the parts and supplied to Chaplane...........obviously through contacts or backhanders or money laundering who knows. My Ferrari 308 has a sort of similar history and when I researched the PO was an accountant who did the books (cooked ) for the company that did the nut and bolt restoration............hence I have a posted here asking if anyone knows any history on the car as it has always been registered from new as 911FVD and despite many owners, thankfully, no one tried to make something from the reg plate and split the two.

Deano I don't think baking parts works after the event............it has to be done within a few hours of plating or other heat treatment where subjected to hydrogen.

https://www.boltscience.com/pages/the-s ... teners.pdf

For sure from one old scientist to another like Covid we can all have our opinions but nothing like hands on and having the heads of screws and bolts break off while actually fitting something.........thankfully never experienced failure in service and I used to do a lot of fault analysis intensive teardowns and support as a subject matter expert on forensic investigations after serious accidents occured with our products.

Steve



Steve

[deano]

Deano I don't think baking parts works after the event............it has to be done within a few hours of plating or other heat treatment where subjected to hydrogen.

https://www.boltscience.com/pages/the-s ... teners.pdf

An interesting point that comes from that magazine article, which you might not want to rely on for anything mission critical, is that it states :

- 8.8's are not susceptible to HE...

That just leaves the 10.9's to deal with then