We just went though a long discussion and quite a bit of research about improving on the fast corrosion and breakage risk of the zinc plated header bolts on the GS500.  The result seemed to be that either stainless steel bolts, or stainless studs fixed in place with grade 272 Loctite, were a step forward.  Loctite did not recommend any of their threadlockers for this application, but confirmed that a lot of people use it for header studs and it generally seems to do OK despite the heat probably being well over spec on the side of the bolt closest to the pipe.  Professional engineering articles on exhaust system materials leaned strongly to stainless and did not even mention zinc (see http://dergipark.gov.tr/download/article-file/318350)  A lot of modification shops are also using stainless hardware.  So, we could feel good about that shiny stainless steel hardware that was much less prone to corrosion, and conclude that Suzuki was using zinc plated steel as a cost reducing measure when they should have paid a little more for stainless. 

OK, continuing to read up on this, it is turning out that Suzuki probably deliberately selected zinc plating to prevent corrosion of the aluminum threads in the cylinder wall.  Yes, the bolt corrodes badly when exposed to salty water and heat, but it is deliberate "sacrificial" corrosion of the zinc in order to PREVENT galvanic corrosion of the aluminum threads.  If the bolt is not replaced quickly enough, then the steel under the zinc starts rusting and the bolt can break during removal.  That seemed to be a design problem that we wanted to fix.     

As a quick technical summary of why the physics actually favors zinc plating, aluminum has galvanic potential of -0.9.  Zinc is -1.25, so with aluminum it becomes the "anode" or "less noble" side that turns to ions and corrodes away.  Stainless steel is about -0.5, so it "more noble" than aluminum and it is the aluminum that corrodes (the more negative always corrodes).  So, Suzuki's strategy here is that the bike owner should be inspecting those head bolts pretty regularly and replacing them.  They're disposable, the aluminum cylinder is not.  They should explain that in the service manual, but my Clymer does not.  Some guys in Tokyo know, but they're not explaining their deliberate use of the zinc bolt as a sacrificial anode.  They probably figured we would have retired our GS500's and moved on to bigger bikes by now, so why waste time explaining every little thing we want to know to keep these low cost bikes in service for decades. 

Stainless steel studs that are well sealed with Loctite to keep out water and in dryer environments may only be causing mild aluminum corrosion, but it's there.  It might be a few years in a wet environment or 40 years in a dry environment, but eventually the aluminum threads get corroded away while the stainless still looks good.  This probably happens faster with stainless bolts that are not sealed or that just have anti-seize. 

If you want further technical details, see https://en.wikipedia.org/wiki/Galvanic_corrosion and the corrosion engineer discussions of stainless bolts in aluminum at https://www.finishing.com/271/67.shtml.

My new stainless studs are going on the shelf, and I'm laying in a supply of zinc plated bolts for regular replacement.  It's a hassle, but that seems to be the way Mother Nature wants it. 

With the greatest of respect...........I think you worry too much 

Maybe so, Sledge, but I did owe it to the members to tell them that the zinc plated bolts were almost certainly deliberate and actually smart.  Too bad--I was looking forward to my new SS studs to sort of "Harley-up" this bike.   

I fitted stainless studs and nuts without threadlock 18 years ago. Nothing has become loose or corroded and the last time I checked the nuts are still free to turn, dunno about the studs but if they have seized.........so what! They don't need to come out and that's the whole point of them.

Your bike, your choice, do what makes you feel warm and fuzzy 

I usually Bitccth a lot about the quality of the screw on GS... I am not talking about the finishing on them.. But they are very soft.. especially the Philips bolts.

I saw many of them breaking and seizing in my " bare hands" many times... as soon I have the opportunity I always put some allens (stainless steel or regular steel).

I prefer to get my chances with a good screw bolt in an perhaps oxidized screw hole.. then a crappy bolt in a "theoretically" sound ( saw a bunch of OEM screws pretty rusty) screw hole.

Maybe I will change my mind in the future....  but not for now.

I liked your post... very interesting. But I will keep substituting mines.. too.

Applaud.

Sledge, at least what seems to be the full story of aluminum, zinc, stainless, and threadlocker is out on the table for the members to consider when deciding what to do. 

It's great your studs are doing fine after 18 years.  If they are corroded in place as you mention to be possible, it's not a problem since they are studs and the exposed threads are not corroding.  So, I could certainly see that being a nice permanent solution, especially if the threads are effectively sealed by corrosion or threadlocker, and salt water cannot penetrate and cause so much further corrosion of the threads that they come loose.   If I were to change my mind and put these new stainless studs on, I'd probably use a LOT of the 650 degF Loctite 2620 and really seal those guys up.  Even with the dissimilar metals and the aluminum being the anode, if the electrolytes (water, salt, and combustion products) cannot get between the metals, there will be little or no corrosion. 

But for someone else using stainless steel BOLTS, if they are in a wet salty environment and their aluminum threads are corroding away, then the time comes when they won't hold a new bolt.

I don't really have anything to add but wanted to say how much I've enjoyed reading this thread and the one that began the debate.  I plan on doing a bunch of non-scheduled maintenance over the coming winter on my '93 and exhaust studs are on the list.  I think I'd rather replace zinc studs now and then than deal with corroded/eroded threads in the head.

Thanks MaxD for the detailed information here. Keep it up! 

One thing I'll point out to the naysayers: usually the complaint is that the Suzuki/stock bolts are weak. This is an observation usually due to them breaking or being subjectively easily damaged during a repair or maintenance. There are few complaints about the factory bolts failing while in use. To me this says they are not weak or too weak for the intended purpose.

It seems to me that corrosion is likely to happen in a couple of places that impact one's perception that the bolt is weak. First is the threads, either corrosion on the bolt or the threads, second is corrosion usually beneath the zinc forming rust between the portion of the bolt/screw that's engaged in the thread (chassis, engine block, a nut, etc.) and the head of the bolt, and thirdly is the head itself. If neglected, then corrosion in the threads where they are engaged will increase the amount of torque required to loosen or remove the bolt. It will also increase the amount of torque required to achieve correct clamping due to increased friction at the thread interface. Rust in the bolt's shank beneath the head weakens the metal there directly making it less resistant to torque. So if you have a bolt with 1mm of rusted shank beneath the head AND corrosion on the threads as installed into the block/head/etc. then it stands to reason that when you begin to remove the bolt or screw one of two things is likely: either the bolt will break in the rusted area beneath the head (happened to me a dozen times), or, particularly on a Phillips-head (or JIS) screw, the head will strip due to excessive torque required to loosen it. In both cases the typical GSTwin forum member will conclude the bolt or screw is "weak" and insist that it's because the bike was "cheap" and Suzuki are just being cheap. The reality is that the bolt or screw was doing its job just fine until you tried to remove it; more regular maintenance might have been in order, like earlier in the lifetime of the bike, remove and inspect bolts and screws and replace when there is any corrosion.

Of course then the shadetree mechanic know-it-alls will replace these corroded screws with stainless screws, and then in another decade when someone goes to remove those they may find that upon reinstallation the hole where the screw goes, into the head or the block etc., has the threads stripped easily. In this case it's because the corrosion has been moved to the aluminum part as you pointed out due to use of a stainless screw. Then said know-it-all will further conclude this is because Suzuki used "cheese" or some other non-quality material for their cast parts. Certainly not because the person doing the modification was misinformed about the side effects.

I agree that Suzuki probably should tell the owners that removing and inspecting zinc-plated steel bolts and screws that are installed into aluminum parts should be a part of regular maintenance if this risk of corrosion is really very high, and maybe the do in the factory manual, IDK. Maybe this is one of the many things that separates the pros from weekend warriors like myself. Or maybe really Suzuki cared mostly about selling the new functional motorcycles and isn't being negatively affected by these kinds of maintenance issues on decade-plus old motorcycles.

GS500s seem to be generally (anecdotally) regarded as pretty bullet-proof and reliable by users and home-mechanics. Maybe this degradation of hardware is just normal wear and tear and there's really no reason to suspect that these bikes are any different than any others. I seriously doubt Suzuki used different hardware material on a GS500 than they did on a Katana or a Bandit or a GSX-R or a Boulevard. It would just make no sense from a supply-chain standpoint. We're not talking about Tesla here, or a company cutting their teeth on manufacturing of big mechanical items. Suzuki has been at this for a long, long time.

Mr72, I've think you've nailed it with describing the physics and human chain of dominoes here and how they can fall leading to the header bolts breaking.  It's a good engineering failure analysis, and reminds me of what the Nobel winning physicist Richard Feynman had to say in his analysis of the O-ring failure that destroyed the space shuttle Challenger.  It's the human tendency to deny physics and statistics that is often the greatest cause of failure.  BTW, I see from your blog that you are in Austin, a great city.  I went to the EE school there at UT, and am in Dallas now.

On this particular issue, the success Sledge reports still has me considering using the stainless studs and really sealing them up.  The Suzuki guys knew what they were doing with the zinc plated bolts, but they did not have the newer higher temp threadlockers available to them at the time they did this design.  Nor did they fully appreciate that they actually did such a fine job in defining and designing this machine that it was going to be so well loved that a lot of guys were going to get into trying to keep them going till Earth runs out of crude oil.  The bike seems to represent the peak of mid-sized parallel twin carbureted motorcyles. I might like to have a new Honda water cooled fuel injected CB500X with 16k mile valve adjustment interval, but I just can't justify it when my GS500 is almost like new, actually does everything I need, and only cost me $70 per year to insure.   

Quote from: MaxD on August 23, 2018, 10:03:08 AM
Mr72, I've think you've nailed it with describing the physics and human chain of dominoes here and how they can fall leading to the header bolts breaking. ...It's the human tendency to deny physics and statistics that is often the greatest cause of failure. 

Yes, I agree with this, however I will point out the counterpoint with an example. I once owned, at the same time, a BMW 530i (70s) and a Datsun 240Z. It so happened that both cars alternators failed at the same time. I changed the alternator in the Z in literally 15 minutes, and the remanufactured part cost about $30. The BMW, on the other hand, took me several days to get properly replaced due to extremely poor design, and a used (and as it turned out, bad) part cost over $100. Both cars had about the same mileage and the BMW was 6 years newer car, and a far more expensive vehicle to begin with. But the Z was designed to be easily maintained while apparently maintenance was an afterthought for the BMW.

So if such maintenance of bolts etc. is required in a GS500 to prevent damage then I believe it's incumbent on Suzuki etc. to instruct users to perform this maintenance routinely just as they do with valve clearances and engine oil. They had to know there was a risk of corrosion that would make repairs (not maintenance) difficult or costly.

I haven't investigated it but I'd have to truly guess that Suzuki probably does instruct (in the FSM) the inspection of bolts on some kind of interval, but it seems like excessive maintenance to those who don't know the cause (like me) and it's often skipped. Heck, my 2015 Jeep sits out there in my driveway anywhere from 2K to 26K overdue for various "inspect" and "replace if needed" maintenance because my experience from owning other cars is that those things should not be at risk of failing this soon... I mean, really, I should "inspect" the exhaust system and belts and hoses in the cooling system on a brand new vehicle with 6K miles? Well my guess is when I finally get around to it I'll find a bunch of degraded and corroded stuff making life a lot harder on me... like I will likely have to cut exhaust bolts that I could have replaced at 12K miles when they started to corrode (and every 12K thereafter) if I maintained it like a race car.

Jeez!
This is a cheap low quality mass produced motorcycle designed for a limited lifespan, not the space shuttle or a nuclear submarine!

If you are all going to get your panties bunched
about a few bolts that in all likelihood will only ever be undone once or twice in the bikes lifetime heaven help you when something far more significant decides to become stuck or shear off.

Mr72, we'd all like to see better design for maintainability in a machine we like, so it is a small kick in the rear that Suzuki did not spend just a little more on the materials in the bike, and provide better maintenance information.  When companies do that, it sometimes really works out great.  The first fighter plane deliberately designed for maintainability was the Northrop F-5.  Designed in the late 1950's, it is so easy and cheap to maintain that it is still widely used today.  This is the plane they were calling a "MiG-28" in "Topgun", and it still holds its own against modern fighters.  A real classic whose chief designer was also the lead engineer for the P-51 Mustang that won the WWII air war over Europe, which shows the influence one engineer can have.   

I've got an old jeep Wrangler also, and like the GS500 it is an enthusiast vehicle.  Even if there are a few places the design and materials are lacking, the nice thing about them is that the interest in keeping them going leads to aftermarket parts and great sources of maintenance information, like this forum.  Forewarned is forearmed, which is what we are getting the benefit of here. 

   

Sledge, 72 and I are engineers, so it has been whipped into us to try to get to the bottom of things.  Sorry if it seems overly detailed. 

Don't remind sledge that I'm a(n) [former] engineer. Please.

Quote from: Kito on August 23, 2018, 04:27:00 AM
I usually Bitccth a lot about the quality of the screw on GS... I am not talking about the finishing on them.. But they are very soft.. especially the Philips bolts...

There are no Phillips screws on your bike. If you're using a Phillips screwdriver, it's very likely that the heads will strip.

Anyone else remember Dennis?
He thought he was an Engineer too!

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

I have been trying to recall past issues I have had relating to stuck/seized fasteners with the GS5s I have worked on over the years. In addition to the header bolts
The list runs to......

Front mudguard fixings
Fork brace fixings
Front disc mounting bolts
Suspension linkage bolts
Fork caps
Form clamp bolts
Chain guard fixings
Fuel cap bolts
Front brake reservoir lid screws
Engine mounting bolts
Banjo bolts going into the brake callers (front and rear)
Air box mounting screws (inserts spinning in the plastic)
Mirror mounts.
Carb inlet boots.

All of which became stuck to the extent that they could not be removed in the way they were intended to be.

I sincerely hope you will not loose too much sleep worrying about yours 

Quote from: RichDesmond on August 23, 2018, 05:48:05 PM
There are no Phillips screws on your bike.

I think maybe we got lost in translation...

I already had problems with screws on the carbs covers, on the ignition sensors fixtures, at the cam chain tensioner cover, front brake fluid reservoir.. well the list can probably go bigger with more brain effort.. ( I bought my gs about  14 months and I already experience bad things with screws..).

Not all got completely destroyed.. but as soon I realize that the screw fitting is not sound and perfect .. I try to change it.

Quote from: Kito on August 24, 2018, 04:48:23 AM

Quote from: RichDesmond on August 23, 2018, 05:48:05 PM
There are no Phillips screws on your bike.

I think maybe we got lost in translation...

I already had problems with screws on the carbs covers, on the ignition sensors fixtures, at the cam chain tensioner cover, front brake fluid reservoir.. well the list can probably go bigger with more brain effort.. ( I bought my gs about  14 months and I already experience bad things with screws..).

Not all got completely destroyed.. but as soon I realize that the screw fitting is not sound and perfect .. I try to change it.

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.

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.