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Discussion Starter · #1 ·
hi guys,

I am quite new to posting here but I have been following this forum for quite a while now. I have a pressing question that I have not found the answer to yet.

I am rebuilding a 1600cc 105.26 engine for a Giulia super and its finally in bits after 2 months struggling to pull the head out.

The Question is have any of you tried to machine the engine studs out of stainless steel? and why it may be a good or bad idea.

thanks

Neville
 

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Richard Jemison
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Studs

Stainless (the alloy in general) does not have adequate tensile strength.
 

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There is also a problem with a galvanic reaction between stainless steel and aluminum which will corrode the studs into the block to the point of becoming unremovable. I just went through an ugly problem with a steel water pump stud and apparently the problem is even worse when stainless is used.

Finally stainless threads can gall and jam the nuts while damaging the studs.

So, weaker, easier to damage the threads, and potentially difficult get out of the block.

Conclusion: probably not a good idea.
 

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Discussion Starter · #4 ·
Finally stainless threads can gall and jam the nuts while damaging the studs.
can you explain this part again please?

I was under the impression that stainless steel is highly resistant to corrosion I was planning to use food or marine grade stainless steel 18/10 or the like.
On the other hand the harder the steel the less it can stretch therefore tensile strength may be a problem.
Another preoccupation that I have in mind is that if the studs do not corrode some other part of the engine might corrode resulting in greater damage.

thanks for the replies guys. I will probably not risk it on this build.

Neville
 

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Finally stainless threads can gall and jam the nuts while damaging the studs.
Lokki is right. I can't explain the metalurgy, but put a ss nut on a ss thread, expose the assembly to heat, and the nut "galls" to the thread. It isn't corrosion - I can't explain the process - but the two become quite stuck together.

I know from experience that this happens on exhaust hardware - I once tried all ss hardware for the three bolts holding the downpipe to the center muffler assembly. After a year or so of service, the nuts could not be unscrewed from the bolts.

My guess would be that head nuts wouldn't get quite as hot as the exhaust system, but I don't know the threshold temperature for galling to occur.

Maybe you could avoid galling by using a conventional steel nut on a ss stud. That question, plus the tensile strength and thermal properties of ss versus conventional steel studs are beyond my knowledge.
 

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I worked in the marine industry all my working life. When you are working with aluminum in that environment, you use ss fasteners to minimise corrosion. Brass and aluminum are an absolute no.

As has been mentioned, ss will gall on ss, also aluminum will gall on aluminum. (we did use some aluminum fasteners in non-magnetic applications)

Stainless is not the end all be all as mentioned. The other thing with stainless you can not burn it with a torch (just melts) so in areas where is is difficult to remove you just can't just blow it off with a torch.

So I would suggest just stay away from non stock applications of stainless in the automotive world, not worth the trouble.

Keep in mind, there are many different alloys of stainless as is true with most metals. Regards, Ian
 

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Another thing to consider: If you put it together right the first time, do you think you'll ever have to take it apart again in your lifetime? If you change the coolant when your regularly you shouldn't have this problem again. Just my 2cents.
 

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The black nitrate coating on my head studs at 45 years old is as good as new. I get a bit of rust on the threads occasionally. If do-it-once is good enough, the OEM set up is fine. I wire-brushed the studs once when the engine was apart, and renewed the coating with a black nitrate solution form Caswell.

;)

Robert
 

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Discussion Starter · #10 ·
The black nitrate coating on my head studs at 45 years old is as good as new.
so from what I can understand you don't change the studs in a rebuild ?

when you need to change them do you think its a good idea to machine them or buy them from the likes of alfaolics and similar shops ?

I hand no idea they had any special coatings.
 

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In fact, it is VERY hard to remove these studs. No, I've never seen them changed unless one got broken somehow. You are as likely to damage the block as to cleanly remove the studs; replacing the block is more likely to happen!

ll the studs in the Alfa block are black nitrate coated, even the little 6mm ones for the water pump.

Robert
 

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Discussion Starter · #12 ·
Thanks for the info. :) however I have something interesting to show you. have to take a picture first. I think one of my studs got repaired somewhere in its life. It's a fairly good job I think, but will post a picture as soon as I find time.

Neville
 

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As pointed out by other posters, the following is very important in determining whether or not one should use a stainless steel alloy in the questioned application.

Some stainless alloys, such as 13-8PH, 17-7PH, 17-4PH, A286, or the 400 series, do have high tensile allowables with tensile strengths as high as perhaps 220ksi; however, some, such as the 400 series, may be susceptible to stress corrosion, leading to tensile failure.

Stainless alloys are generally regarded as gummy steels, and as mentioned, can gall in situations such as threaded joints, or sliding applications, thus basically increasing the friction, potentially locking the joint. Specific coatings are called for to reduce/prevent this galling.

Galvanic corrosion between aluminum and stainless steel can occur, as the anodic index of cast aluminum is around 0.90-0.95, whereas stainless steel is about 0.50-0.60. This is a significant potential difference in a "wet" environment of engine oil (with condensate acids), and coolant, which in many cases is more acidic water than not (due to the lax maintenance by many car owners). Once again, specific coatings are called for.

Doesn't mean certain stainless alloys such as 13-8PH or others are not used as fasteners or nuts, esp in the aerospace industry. Even titanium (generally aluminum coated) is used; however, the aerospace applications for higher strength materials are always design specific, and the fastener materials and their strengths are strictly specified and controlled. Specific coatings for both bolts and nuts are also called for, such as cad plating, aluminum coating, chrome plating, etc. Should be noted that the 400 series stainless steels can corrode because of their low content of chromium.

An interesting site is the following:

http://www.designnotes.com/companion/manual-1.html

So, as advised above and by other posters, the use of consumer available (meaning much less expensive and unspecific) stainless steels for use as automobile engine studs certainly wouldn't be advised, regardless of the available tensile strength of certain alloys. The OEM material applications should be entirely suitable for a long term common usage engine environment, except perhaps for racing (where the engine might be disassembled/inspected/renewed between competitions, thus allowing exotic material short term usage). Provided, of course, that proper maintenance routines, ie, suitable coolant with required renewals, and regular lubricant changes as specified (or more often), are done.
 

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What I have seen is that in engines where the coolant was not well maintained the studs corroded with the head where the stud goes thru the head. It makes pulling the head very difficult sometimes. The coolant on aluminum engines really needs to be changed every 2 years or less to prevent these type of problems. Usually the stud is OK but very grungy; the head corrosion makes sealing at the steel washers a bit iffy, and the head bolts get over-torqued trying to seal the coolant leaks. Lots of bad things comes from that!

Robert
 

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Yup. A Ferrari mechanic I know once spent about 6 months to remove a head from an uncared for v-12 engine because the studs and aluminum head had corroded and filled in the head stud holes with corrosion byproducts. Ferrari had neglected to take into account that owners could be quite negligent in using proper coolant, and changing it regularly.
 

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Many years ago someone made a magnesium anode to replace one of the casting plugs that go-between the cylinders on the Alfa head. I got one, but have well maintained the coolant, changing it about yearly. The anode is still in good shape, but it's nice having an extra layer of protection.

Robert
 

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Discussion Starter · #18 ·
As promised I took some pictures today. Let me know what you guys think about this:
This guy is 2mm longer than the others. It had 2 extra washers on the head to compensate for that.

Galvanic Action
This link will help explain the incompatibility between aluminum and stainless steel.
Galvanic Action - archtoolbox.com
that explains it quite nicely thanks :)

In fact, it is VERY hard to remove these studs. No, I've never seen them changed unless one got broken somehow. You are as likely to damage the block as to cleanly remove the studs; replacing the block is more likely to happen!

ll the studs in the Alfa block are black nitrate coated, even the little 6mm ones for the water pump.

Robert
thank for highlighting that. In fact I have 5 non original studs(with no coating) and the difference is very obvious.
This is the non original one:

and this is an original one:


I am quite amazed myself :eek:

on the bright side its very easy to identify the bad ones because they look like this:


They have obvious machining marks on them.
 

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One thing I've seen with stainless fasteners is that they are not strength rated as are the carbon steel fasteners....think grade 5, grade 8, etc.

Also when machining stainless (316 ss in particular) the material grows alot with heat compared to carbon steel(mild steel or 4140 or etd150). If you use a stainless stud I have a hunch that it may grow enough to allow the head gasket to leak.

To stop stainless fastener galling we use lots of never seize. I'm a machinist in an acid plant, I use LOTS of anti seize.
 
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