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goldgunner's Avatar
 
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REBUILD: 3rd ADVICE REQUEST - PLATING CASE THRU BOLTS

Now well into the case...will be removing the crank, rods, etc. shortly. 1980 911SC 3.0 Bought in May 2005; 188K Miles

In the meantime, looking at the case thru bolts (930.101.173.02):

I'm already stripping, cadmium plating and baking all of the fasteners and hardware from the chassis and external fasteners on the engine (even though I'm also buying new fasteners for the most part).

Question:
I'm inclined to cad plate and bake these case thru bolts. I don't see any cause for concern for having cad plated bolts 'internally' to the degree these thru bolts are internal...I would expect no flaking of the plating.

Same concept to other bolts that do generally 'intrude' into the case and oil environment: examples being - the chain ramp bolts.

So, any concerns to consider?

As always, opinions and perspectives appreciated.

Thanks!
Jim
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1980 911SC - 2nd Rebuild in Process - 2005 Porsche Cayenne Turbo - 2013 VW R
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Old 08-31-2005, 07:47 AM
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What does CAD plate and bake mean? I had most of my external fasteners CAD plated. What is baking?
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Old 08-31-2005, 02:55 PM
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Rule of thumb. Only re-cad fastners that were originally cad plated. I've seen first hand the carnage in an engine that had flywheel bolts cad plated for god knows what reason. CAD does expose the metal to caustic chemicals that can undo heat treating and chemical coatings that reduce fatigue stress. Just my 2 cents.
Old 08-31-2005, 03:08 PM
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No need to all-caps, it is not an acronym. "Cad" is slang for cadmium plating. As the plating is electrochemically bonded and only microns thick, I would not have any concerns about flaking.

The key concern is to make sure, as you mention, that the parts are baked afterwards. Any spring or hardened steel part will be prone to fail if not outgassed in an oven. My local plater told me some great horror stories about customers that, after swallowing $0.87/lb for plating, were too cheap to spend another 50 bucks to bake out the parts. It is absolutely critical that the parts are baked out within an hour of plating, or the whole process is a waste of time and your fasteners are scrap steel.

I'm definitely plating all my hardware, including the through bolts, next time I build up a motor.
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Old 08-31-2005, 04:32 PM
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Dave

Is there any reason (other than looks) to cad plate case through bolts?

Walt Fricke
Old 08-31-2005, 05:15 PM
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The heads of my thru-bolts exhibit corrosion ('rust').
The stripping, cad plating and baking cycles will result in a smooth, deep gold appearance - looking as if the bolts were brand new. Versus new thru-bolt cost, it's an obvious choice.

The cad plating will not only look good for a very long time, but no corrosion will occur for a very, very long time.

Cadmium plate is also recognized for being quite lubricious. In combination with the cad plated cap (acorn) nuts and a small amount of lubricant, to get highly accurate torque installation.
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Old 08-31-2005, 05:30 PM
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Our man from Foat Wuth (love it, its funny 'cause it's true) nailed it. Besides excellent appearance, superior protection and excellent lubricity are offered.

Get a few sets of nuts and bolts together - some old rusty ones, some new zinc plated ones, and some cadmium plated ones. The old rusty ones will feel...well...old and rusty. The zinc ones will feel 'decent' and the cadmium plated ones will feel like they were dipped in machine oil.

Cadmium also completely eclipses zinc plating on corrosion resistance. I've got 30 year old hardware from the undercarriage of my car that still has a beautiful shiny cad finish, while I've got brand-new zinc dichromated parts that have lost all plating qualities after six months.

The drawback to the enthusiasts like us is that cadmium plating is extraordinarily expensive, over 4 times the cost of zinc plating at least here locally. This is due to the low volume of cad plating these days. The reason behind that is EPA regulation - cad plating involves some really nasty chemicals (like cadmium for example, ha) and in most areas now requires expensive closed-loop systems to protect the water supply.
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Old 08-31-2005, 06:50 PM
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Cadium v Zinc plating issue is addressed. The appearance of the Zinc certainly is acceptable, but I would like better longevity from Zinc. Who does Cad in Florida?

Thank you.
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Old 09-01-2005, 07:01 AM
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Bling. No reason other than cosmetics.
Old 09-01-2005, 08:25 AM
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Hmmmm....Let's see...

Supertec cadmium plates the engine baffles on their high end rebuilds; my engine baffles going into my rebuild have significant rust in some areas - cadmium plate would prevent that rust...

My case-thru bolts have rust on the bolt heads and some under the heads, beginning to form on the filet radius under the head - cadmium plate would prevent that rust, and thereby preclude intergranular stress corrosion in that critical head to body filet radius area...

My case has many studs with mild to very severe rust and corrosion, some of which has propogated all the way to threads that were within the case - cadmium plate would prevent that rust...

Bling? Cosmetics only? I don't think so...
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Old 09-01-2005, 09:07 AM
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QUOTE: "As always, opinions and perspectives appreciated."

That doesn't appear to a true statement, does it?
Why did you bother to ask if you already had an answer stuck in your head?
Your engine is 25 years old. So are the fasteners.
After 25 years they are starting to show corrosion. Who'da thunk? If you really want to, go ahead and spend the money for the bling.
A wire wheel and some rustoleum or never-sieze will get you the same amount of protection 5 years from now.
Old 09-01-2005, 01:50 PM
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err sorry Sammy, I really wasn't being combatative (I leave that to my wife - mostly).

Please recall my original question was regarding using the cadmium plate in INTERNAL (case) locations - where bling would have no context.

In answering your bling thing, I was changing the subject to the EXTERNAL (case) locations - where bling would have a context.

Anyways, thank you for your opinion and sorry I sounded confrontational - not my intentions at all.

Jim
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Last edited by goldgunner; 09-01-2005 at 02:01 PM..
Old 09-01-2005, 01:58 PM
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Hmmm, if bling were the only factor, I think I'd be paying 1/4 the price and getting zinc...
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Old 09-01-2005, 08:11 PM
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Be careful if you Cad plate 911 hood and trunk lid hardware. The collar or plunger that retains the large spring is made of pot metal, and when it's put in the acid bath, it disintegrates without leaving a trace. You can't buy that part separately from Porsche -- or anywhere. I lost four of them when I did a batch of plating recently. I suppose you could have some made, but it would be a big pain. Be sure to hold those parts back in your shop...
Old 09-06-2005, 05:38 PM
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Quote:
Originally posted by Rob 930
Be sure to hold those parts back in your shop...
As well as any AL MFI linkage. I made that mistake.

Back to baking. Only cad requires heating, or both cad and zinc? I know the guy who did my cad did not heat the parts and some suspension bolt broke while I was reinstalling them. I read here about the heating and threw the stuff away. Next batch I did the zinc. Not too many bolts that hold anything important in that batch, but what about heating yellow zinc?
Old 09-08-2005, 07:43 PM
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Baking

Baking applies to both zinc and cadmium plating.
Actually applies to any plating 'bath' where there are free hydrogen ions.

Typically baking applies to alloy steel with a hardness of Rc37 or harder and ferritic stainless steels (eg 17-4PH). Grade 8 and Class 12.9 fasteners are of this level hardness. Grade 2, Class 8.8 and Class 10.9 are not - but it doesn't hurt to bake and be sure.

Typical specifications require a 4 hour minimum bake at 350 degrees F within 1 hour following plating.

Fasteners and components that are 'high reliability' - like flight safety items - require a 24 hour bake cycle.

All post plate baking is to minimize the potential for hydrogen embrittlement - baking the hydrogen out before intergrannular embrittlement occurs on a crystalline level that would create a weak point for material failure to occur.

Note that the key operative word is 'minimize'. Despite close adherence to the complete baking regimen hydrogen embrittlement and potential failure can still occur. Sometimes the bear wins...

Additionally, some specifications call for a pre-plate 'stress relief' bake. This is in high strength materials to 'relax' crystalline areas stressed in the component formation / machining that are thought to be more susceptible to post-plate hydrogen embrittlement.
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Old 09-09-2005, 04:03 AM
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Old 09-09-2005, 07:17 PM
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Wow, I almost understood that! I love seeing the knowledge on this board.
Old 09-09-2005, 07:49 PM
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