SUMMARY:  We got into this discussion to understand what was the best way to deal with the corroding header bolt problem.  The whole issue of steel bolts in aluminum threads is filled with misinformation and lack of understanding (just try a web search), even among many professional maintainers.  It runs the gamut from many maintainers saying "Just do it!" to discussions of how the new U.S. Navy ship USS Liberty has been nearly ruined by it.

Turns out our bolt corrosion was not really a "problem", but a form of solution that just was not explained by Suzuki.  Their zinc plated bolts corrode as deliberate sacrificial anodes to save the aluminum threads, and are intended to be replaced when the zinc is mostly corroded off them. 

To get around that regular maintenance, and just ugly corroded bolts on our bikes, Sledge has had what seems to be good long term results (18 years) with stainless steel studs in his particular riding environment (salty water exposure not known).  The aluminum threads may be corroded inside (they are galvanically sacrificial to stainless), but so far they have held.  It is likely that the highest temp version of Loctite available (650 deg F) can seal them fairly decently so that corrosion is limited.  We have measured the temp on the outside of the bolt carrier farthest from the pipe at a little over 400 deg F, though it may exceed 650 on the side of the bolt closest to the pipe.  But, exceeding the temp spec by a moderate amount does not immediately destroy the Loctite as a sealant--it just renders it weak in grip force.  The makers of Loctite have not measured the "burn temp" of the Loctite to say for sure when the Loctite is destroyed and will no longer even function as a sealant.   So, using stainless studs with 650F Loctite is likely, but not guaranteed, to be a sound long term solution.  If the hottest any part of the seal gets is not more than 750 deg F, then the seal almost surely holds. 

There are a few things left we could do to get better understanding:
1.  Measure the temp on the inside of the bolt closest to the pipe (my electronic temp probe won't handle it).
2.  Consider aluminum bolts or studs to match to aluminum threads.  Aluminum bolts and screws are made, but they are much less available.  There is a company in the United States, Aluminum Fastener Supply, that specializes in this.  They claim the reason aluminum is not more used is not the strength of the bolts, but just an historical mistake that has not yet been fully corrected.  They say their business is rapidly growing, being strongly driven by the use of aluminum engines in cars and more use of aluminum fasteners on those American cars.  Unfortunately, they don't make metric products. 

Sledge, the discussion is not a shot at you.  It's just physics, buddy.  But, if you want to see just how fast and bad the stainless to aluminum corrosion can be, look up the "lasagna cell".  Lasanga (or any salty tomato based food) in a stainless steel pan with aluminum foil on top will corrode holes into the aluminum foil overnight.  This is shown with pictures at https://amazingribs.com/more-technique-and-science/more-cooking-science/beware-lasagna-cell-how-some-metals-can-ruin-your
     

Quote from: qcbaker on August 24, 2018, 05:44:34 AM
Rich is right, there aren't any Phillips screws on these bikes from the factory. Suzuki uses JIS screws, not phillips. If you try to remove a JIS screw with a phillips screwdriver, you will almost certainly strip the head.

Come on...

I though there was just philips and PZs slots... JIS.... JEsus.. F#$$%  Christ.

Either way I hate this kind of drivers....  really.. and now.. more then ever.

You got me good Rich.. thanks for teaching me this one!

Well, it is not a guarantee that you will ruin a JIS screw head by attempting to use a Phillips screwdriver on it. I have done it hundreds of times on my own GS without any problems at all. Using too-small Phillips screwdriver or a badly worn bit will likely screw up the heads. Trying to remove it at a weird angle where you can't get enough force downward into the screw head will also improve the likelihood that you screw it up. But it's certainly not assured that you will screw them up.

However, if the screw is stuck due to corrosion, and if it's weakened because of rust, then no matter what type of screwdriver you use, you will likely damage the head.

FWIW I have never damaged a JIS screw with Phillips screwdrivers on my own 26 year old GS500. But I have snapped off numerous 8mm-head case screws, rounded the inside of an allen-head bolt holding the heel protector on, and in many cases I've elected to replace JIS screws with allen screws when I have to work on that part. I kind of have the sense that this JIS screw thing is a lot more Cliff-Clavening by GS500 owners. Look how smart everybody will think I am when I can point out some trivial thing they are all wrong about!! nyah-nyah!

It may have been a placebo-effect, but I felt that my JIS driver is what helped remove a lot of my carb's screws (but still not all), in comparison to the good quality Phillips driver that seemed to cam out at any opportunity. Maybe not so coincidentally, JIS is mostly mentioned alongside carb topics online (in my research), so it seems that's where the issues are most prevalent.

I much prefer hex key drives to JIS/Phillips/Pozidriv too, but even they're still easy to round out in mildly corroded fasteners. I rounded a allen head footguard bolt the other day too mr72, but luckily managed to cut a slot in it and use a slot drive. Hence my preference for stainless, because as with Kito, I'd rather have a solid head in a potentially corroded thread, than a corroded head and thread. (Stainless Torx drives would still be my ideal!  )

MaxD, I've also considered aluminium fasteners before but just shrugged it off. I suppose they're usually ignored due to their insufficient strength in many circumstances, but the GSs low recommended torque of 9-12 Nm for these headers should be fine unless I'm missing something glaringly obvious? Aluminium and its alloys all obviously have lower Young's moduli and yield strengths than the steels we use, but they must be capable of a measly 9 Nm? I suppose you'd just have to be extra careful not to over tighten them as you'd already be borderline (maybe a lack of redundancy is the issue and reason for not being used? or fatigue?)


Edit:

Pro-Bolt, a UK aftermarket fastener company, sells M8 size aluminium bolts and suggests maximum torque values of 8 to 12 Nm (https://www.pro-bolt.com/torque-information/). Although unsurprisingly they suggest to "not use aluminium bolts in any stress areas e.g. Brake Caliper Fixings, Suspension Mounts, Footrest Hangers, Grab Rails etc."

Max, I tried a search on why aluminum screws and bolts are not more common, and I did not get any authoritative results.  The lady I talked to at Aluminum Fastener Supply was the wife of the founder, and though she was knowledgeable, she was not very technical.  She has a tech guy, but he was out this week.  She did point me to a larger company, Bossard (HQ Switzerland), that I left a tech support request with.  I'm guessing it is not JUST history and standard practice that are holding back aluminum fasteners.  The head is pretty soft and easy to strip, and there may be corrosion effects as theorized below. 

Aluminum has a very slow oxidation process.  Bare aluminum develops a coat of aluminum oxide a few nm thick in a few months, which is an electrical insulator.  When this coating is developed on purpose, it is called anodized aluminum.  Whether nature does it or a deliberate process, once it is on there it inhibits further corrosion, which is why aluminum can last many decades (if not galvanically mismatched) even when exposed to weather.  I had an unpainted aluminum 1946 Cessna 140 light aircraft that was over 60 years old and had no corrosion. 

My guess is that the main reason aluminum threads do not almost instantly corrode away with stainless bolts is that they are often coated with aluminum oxide when the bolt goes in.  It's fairly tough stuff, and if the bolt does not scrape it off, then there is probably some protection provided by that (since it is an electrical insulator, it should inhibit the galvanic process).  However, if a new, not yet oxidized aluminum bolt or screw is set into new aluminum threads, then the oxidation process MIGHT fix them together pretty firmly.  Trying to remove the bolt/screw may then round off the bolt head or screw slot, since the aluminum is pretty soft compared to steel.  Similarly, if an aluminum bolt/screw is set into steel threads, then the aluminum becomes galvanically sacrificial and is weakened, and might be pretty easy to break off. 

I don't really know, but my guess is that some combination of these potential problems has prevented aluminum bolts and screws from becoming more popular.  I'm an electronics engineer, and don't belong to any mechanical or material engineering professional organizations that might have professional articles on the subject.  If we have any mechanical engineers here on the forum, perhaps we could get them to explain it, or use their professional membership article access to get to the bottom of it. 

Take a Phillips screwdriver, one closest to the JIS screw you wish to undo. Grind/file about 0.050" off the point. Ok it doesn't make it a JIS screwdriver but it will fit the JIS head a lot better and reduce the chance of camming out and rounding off the head.

Ask any half decent Engineer 

I do see where you are coming from...

Quote from: qcbaker on August 24, 2018, 06:02:13 AM

Quote from: sledge on August 24, 2018, 03:06:06 AM
Anyone else remember Dennis?
He thought he was an Engineer too!

http://gstwins.com/gsboard/index.php?topic=68354.0

I really hope that one of these days you learn that being right isn't an excuse for being an @$$hole. You have a useful wealth of knowledge and experience that we all could learn from if you would just share it politely. However, instead of doing that, you always seem to insult people and seek to destroy everyone else's credibility. Dennis might have been wrong about honing cylinder walls, but he was right about you when he said you're arrogant, nasty, and mean.

Arrogant, nasty and mean?
Nahhhh......You have got me wrong. I am just allergic to bullshitters 

Quote from: sledge on August 24, 2018, 12:34:32 PM
Ask any half decent Engineer 

Naaaa, we got engineers these days who don't know how to hold a wrench (spanner - translated just for you sledge)
We need to ask an engineer with some grey in their hair ...
And yes shaving the point a bit helps - not just with the JIS crap but also most screwdrivers start necking at the point and a tiny bit up from there.
Cool.
Buddha.

Checking Amazon for useful books on corrosion and material selection, I find that the professional books run $100 to $200 each.  It's quite a complicated subject, and the professional books get quite detailed on the theory (many are graduate level engineering text books).  There is quite a selection since corrosion is such a problem, costing about 4% of GNP and about $1000 per person per year.  Checking inside them as far as Amazon lets you does not seem to turn up the information we need on selecting best fastener materials and methods in easy user guide form.   

This downloadable free book seems to do about as well:
http://dl.iran-mavad.com/pdf95/Corrosion%20Control(Casti%20Guide)_iran-mavad.com.pdf

The author seems a solid pro (BS, MS, PhD) with over 30 year of experience in corrosion control.  There is one short but applicable chapter for us, which is Chapter 17 "Designing to Control Corrosion".  He does not get into a lot of detailed guidance here, perhaps because he makes his living providing additional detail and does not give it away for free.  But, the basic strategy of practical corrosion control from the product designer and user point of view is described as:

1.  Control the Environment (chemical exposure, heat, etc)

2.  Metal Choices
A. Make allowance for inevitable corrosion and its rate.
B. Ensure galvanic compatibility.

3. Inspection and Maintenance (As 72 points out, the designers really intend certain fasteners to be periodically replaced)

I am still stuck trying to get the original ba***rd things OUT of my GS...The allen hex heads are rounded totally and so far all attempts with sawed slots in them or get vise-grips on have failed totally. I have a mate who is going to help me weld some bar onto them to try to get them turning, or maybe just grind the heads off and drop the whole engine onto a drill press to get stud extractors into the remainder on the bolts. Not even going to bother considering what to replace them with till after, but my tentative options are simple A4 stainless allen bolts or stainless studs with brass nuts if I feel fancy.

What we really need is an authoritative article directly on the subject of best fasteners and practices for aluminum engines.  I have not been able to find that, but I have found a bit more useful information. 

Racetech Titanium is an American operation that makes mostly titanium fasteners, but also some aluminum.  Their website is:
https://racetechtitanium.com/index.php?main_page=index&cPath=143_36&zenid=f5a28c27a93720aad02bb9790955dc4d

I talked to them hoping for information on aluminum bolts for the GS500 headers, but they don't make anything that fits.  Their specialty is titanium bolts aimed at motorcycle racing for weight reduction, mostly motocross, where they say they are in almost all the equipment.  Titanium is even harder on aluminum than stainless, but in in this application that is acceptable because:
1.  They don't expect long service life from racing engines.
2.  While that engine is in service, it gets a ton of maintenance.  The titanium bolts are in and out all the time, and every time they go back in they get a new application of anti-seize, which should provide at least a period of corrosion inhibition by blocking water penetration. 

For general purpose corrosion information, the British operation "Corrosion Doctors" is excellent.  In particular one page on their site has a number of downloadable pdf's on different aspects of corrosion control.  That page is:  http://www.corrosion-doctors.org/InternetResources/NPL.htm#Control

I still have found nothing to indicate that Suzuki's strategy of a zinc plated sacrificial anode bolt that is periodically replaced was not a sensible approach.  Sealing off a stainless stud may do fine also, but we don't have any data.  Sledge has had unsealed stainless studs in one machine for many years, but we don't know how the aluminum threads are really doing (they might just crumble to pieces if the stud is ever removed). 

Quote from: sledge on August 24, 2018, 03:06:06 AM
Anyone else remember Dennis?
He thought he was an Engineer too!

http://gstwins.com/gsboard/index.php?topic=68354.0

Wow blast from the past.

BTW I dingle balled those walls, and it's still going strong. I think like 120PSI on the cylinder. 

Don't tell Dennis, he will throw a fit 

The main professional organization for corrosion engineering is the National Association of Corrosion Engineers at:

https://www.nace.org/home.aspx

Lots of good material here, but I did not see anything specifically aimed at fasteners for aluminum engines in the main material or public white papers.  However, since I am not a member, I don't have access to the thousands of articles published in their several journals over the years.  More authoritative answers on best material and practices for aluminum engines are probably in there, if we can locate someone with access. 

The recommended provider for the stainless steel exhaust studs in the U.S. was referenced via eBay link as "Jon's Auto Shack", where I ordered the studs I now have.  I pinged the owner for his understanding of the corrosion problem and the particular stainless he used.  He provided the thoughtful reply below:

"Good morning,

I would like to apologize for the few days late reply as things didn't go as planned on Friday and I wasn't able to get back to you as I said.

The 'off road only' reference is just as you said, legality. Since this item (along with others that I make/sell) can be construed as being part of the emissions system, I need to include it so I don't get in hot water with anyone doing modifications of their vehicle.

As for the quality of the studs, these are A2-70 stainless. This means they have a composition of approximately 15%-20% chromium and 15%-19% nickel, which is higher than your typical 304 stainless.

I completely understand your concerns with the galvanic concerns. This comes up almost every time someone goes to replace their OE studs with what they are hoping to be longer lasting stainless. This is one of the reasons I include the copper anti-sieze with the kits. The combination of both the copper flecks (an inert metal that helps isolate the stud from the threads) combined with the solution that it's suspended in, helps act as a dielectric barrier to further help prevent this galvanic issue.

Typically speaking, unless you don't ride often enough, let the vehicle sit for extended periods of time, or live in a high salt water area, the hot and dry environment of an exhaust system helps drive water based electrolytic liquids out of these areas.

If you still have concerns with using these in your GS500, A4-70 studs would be the next option as they have an even higher resistance to galvanic corrosion.

I hope this helps and if you have any further questions, concerns, or really anything, please don't hesitate to ask!
- Jon"

This horse has just about been beat to death, but here are a couple of significant inputs to get the issues nailed down for good (I know I've had enough).

First, you guys might be interested in what a PhD level mechanical engineer and materials scientist I used to work with years ago, and tracked down to ask about this issue, has to say about it.  This guy is a great mechanical engineer, who specialized in high temperature materials and design and thus had four graduate classes in corrosion (most ME PhD's have maybe one or two), and here is his opinion:

"Interesting and accurate analysis. You are using the galvanic corrosion theory correctly. The Electromotive forces (EMF) tells a lot about a metals stability/reactivity.  When you compare the standard reduction potential (as you did)  Al vs SS you will find that the Al is most likely to be attacked (higher negativity - thus the anode).  So, when your case is out of Aluminum the stainless steel bolts will essentially be inert because ions from Al will flow to the SS screws.  Hence, the set-up (Al Case and SS screws) will be very benign especially in the absence of a liquid.   The oxide formation on Al is another challenge.  Al will form an oxide layer as soon as it is exposed to air.  Al is very reactive to O2. 

What you have to watch out for is Al+3 ions flowing towards the SS threads which may make it difficult to remove the SS bolts later.  For this to happen, the electrons have to flow from the SS bolt head via a medium onto the Al surface.  The "galvanic cell" is complete when the ions from the Al are deposited onto the SS threads.  Hence, pitting will occur on the Al threads against the SS bolt threads.  Oxidation and reduction bi-products only serve to complicate what is going on.  With respect to Loctite and other barriers, I have read many corrosion documents that say these barriers work great EXCEPT when the barrier is damaged and the "galvanic cell" can be completed.  In doing so, the amount of electrons flowing from the SS bolt to the Al housing will remain the same, but the ion transfer will increase at the defect.  In essence, Al+3 ions must balance the flow of electrons (1 Al for every 3 electrons).  We were taught to not count ions but consider them charged holes.  The number of holes has to balance the number of electrons.  So, when you get to the complexity of oxidation and reduction reactions occurring at the same time as positive ions and electrons flowing, you balance the holes and electrons first, then you balance the charged ions to account for all the potential species forming using a ratio based on the EMF values. 

In short, you are right, the Al engine block is being protected by the sacrificial zinc coated steel screws.   SS screws will have a "long" term negative effect on engine blocks.  The reason I brought up balancing holes and electrons is that as the temperature increases more holes and electrons are flowing in opposite directions to complete the galvanic cell when a medium is present.  The problem is exacerbated when Loctite or a barrier is used which fails and focuses the ion transport within the failed site.  We were told (30 yrs ago), that your better off not using a barrier to inhibit corrosion, because if the barrier fails you localize the corrosion."

Second, Bossard, the large Swiss fastener company, also got back in touch with me today.  I spent about 15 minutes on the phone with the senior applications engineering manager who handles their corrosion resistant fasteners in North America.  He confirmed also that the zinc plated steel is a deliberate sacrificial anode that is widely used in the automotive industry with aluminum engines.  He says anodized aluminum fasteners would have longer service life, but the problems are that the cost is 8X as much, and people tend to forget they are aluminum and over-torque them.  Between the two problems, aluminum has just never caught on, even though in an engineering sense there are many low-torque spots where it would be the ideal solution.   

I guess that pretty well settles the questions.  It's stay with the zinc plated bolts and regular replacement as Suzuki intended, or throw the dice on the aluminum thread corrosion rate that will inevitably occur with stainless.  Aluminum could work, but getting the hardware that will fits and remembering to be careful with it are the issues.   

Thanks MaxD, I really did appreciate reading all of that.

From a practical point of view, it seems that the zinc-plated steel hardware is sufficient to do the job but may require more frequent replacement to prevent failure due to over-corrosion of the steel part. So again it's neglect of maintenance (unintentional for sure) that creates the perception amongst GS500 home mechanics that these bolts are "weak". OTOH a stainless stud or bolt would be a far longer-lasting fastener but you may wind up corroding the aluminum head which is much more difficult and expensive to replace. In the end the result from a maintenance perspective may be the same: the bolt breaks when you try to remove it.

So the moral of the story is: do frequent inspection of zinc-plated steel bolts and replace once they show any signs of corrosion and your bike will be happy and easy to work on for years to come. Failing that, you likely will break the corroded bolt and have to work to extract it, but resist the temptation to replace the bolts with stainless steel bolts, but rather replace with equivalent zinc-plated steel bolts and reduce your inspection interval to ensure the replacement bolts don't corrode and then fail.

That said, I did put SS bolts in my engine block when the originals broke. I suppose I should revisit that decision. Maybe I need to order a bunch of OEM Suzuki case bolts.

Thanks for working on this very informative thread MaxD!  I have also heard folks saying that they would never use stainless fasteners or parts as stainless is brittle and can fail due to fatigue in motorbike like environments but have never been able to confirm that in my own research.

72, I personally will probably be laying in a stock of the zinc plated Suzuki OEM bolts, even though they are overpriced at $3 each.  Bike Bandit sells a set of 12 Vance and Hines for $5.99 (V&H part number V22533) that their search engine takes you to for GS500 header bolts, but Bike Bandit tells me they are unplated.  That may not be right, so I tried to check with V&H directly, but they say they did not intend those bolts as exhaust header bolts, and they could not confirm the plating either.  Since so many guys here have reported breaking off these bolts, I'm wary of substitutes.  I don't doubt there are zinc plated M8-1.25 substitutes out there that are as good or better than Suzuki OEM for lower cost (bags of 100 in grades 8.8-8.9 are around $0.30 per bolt), but we would need to be quite sure of the quality of the steel.  After talking to K&L about their valve shims, I had good confidence their half price substitutes were good quality (their apps support was really alert).  I don't have a substitute here that I have reason to trust.  Maybe some of the other guys are aware of the steel grade issues involved, and can recommend a cheaper/better substitute.