Main things to look out for?

[Endopotential]

Going for the eBay penny pinching prize, I'm gonna try this...

https://www.ebay.com/itm/263307585860
https://www.ebay.com/itm/253539179260

Stainless studs and acorn caps for about $12 

[max]

He also used anti-seize and not Loctite on those header bolts. 

Don't put anti-seize on header bolts, or any other torque critical fastener


If you lubricate threads it reduces the amount of torque needed before they yield meaning if you do apply the recommended amount of torque you will weaken the bolts or strip the threads because of the now reduced amount of friction between the male and female. If you do then reduce the amount of torque applied you also reduce the clamping force between the port and flange meaning the gasket will be prone to leak and the bolts themselves may even loosen off due to the heat cycles.

I had this argument with him when he was alive, he wouldn't have it. I hate to think how many people took his advice on board and went on to have problems because of it 

It might be the wording, but I disagree that reducing the torque will reduce the clamping force (assuming higher torque dry threads vs lower torque lubricated threads).

Tensile clamping load and fastener torque are usually empirically related by Load = Torque / (Thread diameter * K), where K is basically a friction coefficient (K_dry > K_wet). So you can obtain the same clamping force for a dry vs wet thread by respectively increasing or decreasing the torque on the fastener.

Of course we're assuming all parts are within their elastic ranges and ideally we would just be measuring bolt strain rather than torque in the first place etc etc.

Completely agree re anti-seize increasing the chances of bolts loosening due to vibration and heat-cycling, and let's not forget that thread locker will also initially act as a lubricant so any torque values used should also be marginally reduced.

I'm of the opinion that the stainless hardware should be fitted dry into the head as the galvanic corrosion is unlikely to have any significant impact - in fact a small amount would be beneficial in ensuring the fasteners don't work themselves loose as discussed.

A closing note for completeness sake, but stainless shouldn't be used for any high-torque fasteners anyway. A2-70 stainless only has a ultimate tensile strength of 700 N/mm² which is much lower than than the grade 8.8 or 10.9 steel fasteners used in the more heavily loaded components.



Related to this, but more on-topic to the thread, I've been slowly replacing the non-critical fasteners on my bike with stainless ones because of my pure hatred for rounded and/or Phillips drive fasteners! I'll be slowly updating the wiki (http://wiki.gstwins.com/index.php?n=Restoration.BoltSizes), with my measurements as I progress if anyone ever fancies doing the same.

[MaxD]

I'm not a mechanic, so can't easily sort out the conflicting advice from experts like Sledge and Adidasguy.  What they have done has worked out well for them. 

I do like seeing the math presented by Max, which seems to indicate that if you are careful with torque the anti-seize is OK.  I would assume that if you check your header bolt torque pretty regularly, like every time you lubricate your chain, that anti-seize or nothing at all (as preferred by Max) are probably OK.     

But, here is a pretty professional reference that leans to using Loctite:  https://www.bmw2002faq.com/articles.html/technical-articles/engine-and-drivetrain/installing-exhaust-manifold-or-header-studs-r30/

This is a BMW car article, but it makes a good case as follows for how to best install header studs. First, tighten the stud only finger tight, but use Loctite.  It then goes on: "So, why is it wrong to tighten the stud into the hole? Unfortunately, I have even seen it done by supposed "professionals". The way a stud can outperform a bolt in clamping efficiency has to do with the even distribution of stress across the engaged threads. If you torque a stud into a blind hole, you lose that benefit, and concentrate stresses at the first thread in the hole. If you torque the shoulder of a stud against the edge of a threaded hole, you lose the benefit & usually distort the mating surface. It's not as if there is a suitable bearing surface to take the load. Just don't do it. Loctite threadlocker is the answer for securing the stud (for most of our situations)."

So, what this BMW author is saying is that if the stud is tightened down, then when the nut over the clamp is tightened it pulls only against the first one one or two threads on the stud.  I assume this could pretty easily bend them for aluminum threads.  But, if the stud is a little loose, then the nut exerts an outward pull on the stud that is engaged over most of the threads in the aluminum cylinder head, with much less likelihood of bending the threads. 

Based on that, I think I'll go with Sledge and BMW on using the Loctite.  For the OEM bolts the Loctite may later increase the risk of breaking a badly corroded bolt, but for higher quality stainless steel studs that corrode slowly and where that rate is further reduced by the Loctite, they can probably be gotten out later if need be.   

[MaxD]

Endopotential, I looked at those ebay studs, and they are 40mm.  It was reported earlier in this thread that for stock headers you need 60mm.  I measured on my own stock headers, and if the hole is 25mm earlier reported, then I measured a need for 55mm minimum on the stud.

[Kilted1]

He also used anti-seize and not Loctite on those header bolts. 

Don't put anti-seize on header bolts, or any other torque critical fastener


If you lubricate threads it reduces the amount of torque needed before they yield meaning if you do apply the recommended amount of torque you will weaken the bolts or strip the threads because of the now reduced amount of friction between the male and female. If you do then reduce the amount of torque applied you also reduce the clamping force between the port and flange meaning the gasket will be prone to leak and the bolts themselves may even loosen off due to the heat cycles.

I had this argument with him when he was alive, he wouldn't have it. I hate to think how many people took his advice on board and went on to have problems because of it 

I see what you're saying and agree.  To re-state, since there seems to be some dispute on the point:  Clamping force of a bolt is a direct function of turning, of which torque is simply a relative measure.  Lubricating the threads makes them turn easier, no brainer there.  With a lubricated fastener, the same clamping force will be achieved with the same amount of turning but at less torque.  To achieve the same torque requires more turning.  The potential for over-clamping (warping parts), stretching or breaking the fastener, and/or stripping threads is quite real.

Torque specs are always assumed to be dry unless otherwise specified.

If you're concerned about it, maybe the best solution is to add it to your annual winter maintenance.  If you insist on using compound to save yourself 15 minutes a year, you should reduce the torque.  By how much?  I have no idea!  Swapping out the exhaust studs for stainless does sound like a great idea though.

[Endopotential]

Endopotential, I looked at those ebay studs, and they are 40mm.  It was reported earlier in this thread that for stock headers you need 60mm.  I measured on my own stock headers, and if the hole is 25mm earlier reported, then I measured a need for 55mm minimum on the stud.

I have stock exhaust headers, and took out my bolts to check.  The threaded section on them is 40mm long, which seems like plenty.  I can't image there's an extra 20mm of threaded hole in the cylinder head.

I'll let you know once the mail from China arrives in 2 weeks or so...

[MaxD]

Endo, I took this measurement again.  From the face of the hole in the cylinder outward through the collar to the TOP of the bolt head I measure 32mm (I had 30mm the first time I tried this).  I measure the bolt head as 8mm, so the collar is thus about 24mm.  The hole (which I have not measured) is reported as bottoming at 25mm, though it is not a given that the threads go all the way to 25mm.   

So, your 40mm thread should go about 40 -24 = 16mm into the cylinder.  That seems like plenty of mated thread to me.  So, I retract the link to the Amazon 60mm bolts--I was wrong to assume that 60mm studs also meant 60mm bolts. 

The stud situation would seem a little different.  The minimum length of the stud IF the stud screwed all 25mm to the to the bottom (I don't know yet if it can) and if the nut used is as thick as a bolt head would seem to be 25 + 32 = 57mm.  The members here have several times quoted 60mm, which would then let about 3mm of stud thread come through the nut after it was tightened.  That 3mm would allow a washer under the nut if desired. 

But, if the stud is only screwed in about the 16mm that your bolts apparently go in, then the minimum stud would be 16 + 32 = 48mm.  If the 60 mm stud goes in only 16mm like the bolt, then the stud is going to protrude about 60 (total) -16 (into cylinder) - 32 (collar + nut) = 12mm above the nut.   

We have about 10mm variation here depending on how far the new stud is screwed into the cylinder.   If it only goes 16mm in, we could probably get by with a 50mm stud.   

[sledge]

http://www.zerofast.com/proper-bolt-torque


Explains it better than I can

[MaxD]

Sledge, the torquing issue as described in your article pointer above is obviously critical for the case of header bolts. 

But, what is your advice on header studs?  I assume you saw the pointer to the BMW article above that recommends just tightening header studs finger tight, but with Loctite to prevent them coming loose, and then allowing the tightening of the nut to tension the stud against nearly the full length of the cylinder threads.  Did you agree with that?

[J_Walker]

all this talk about bolt torques, Just use the grunt system.. soft grunt, 20ft.lbs. medium grunt, 45ft.lbs. heavy grunt, 70ft.lbs. Swift kick, 200ft.lbs. 

[ShowBizWolf]

IIRC, when I installed my studs, they wound/threaded in the full 25mm and bottomed out there.

J_Walker, that's funny stuff

[MaxD]

Thanks Showbiz.  It seems we have all the information we need to do a perfect job on studs replacing bolts, with the exception of just how tight those studs should be torqued in.  BMW says finger tight, but unless I hear otherwise I'll do 'em a little tighter than than, with Loctite on about the first 12mm of the 25mm so that the chore of possibly getting them out later is not severe. 

[MaxD]

One more piece of information could be useful here--which version of Loctite so that it holds but you can still get it out later.  Here's a mechanical engineer's posting on this issue:

"There are different type of thread lockers that are used to basically 'lock threads' of the bolt from loosening due to vibrations. Depending on the thread locker used and the size of the bolt to be loosened, the method to loosen the bolt varies.

If it is a low strength or wicking type thread locker (ex. Loctite 222), simply applying some extra torque using a spanner or screwdriver would do the job. (Generally used for small size screws and bolts)

If it is a medium strength or 'blue' thread locker (ex. Loctite 243) , simply applying the breakaway torque with a torque wrench or pipe would loosen the bolt. (Generally used for medium sized bolts )

On the other hand if it is a permanent strength 'red' thread locker (ex. Loctite 270), you would need to heat the assembly and then apply torque to loosen the bolt. Should do your job "

Apparently if you using the "red" stuff, Loctite 270, better have a torch handy to get that stud out. 

[MaxD]

Holy cow, the red stuff is like welding it in.  Posted directions for removal as follows.

"Attempt to remove the bolt first with the correctly sized end wrench or socket. Purple 222 will break free with 20 foot-pounds of torque or less, while Blue 242 will hold to about 50 foot-pounds. If you've got red Loctite, don't bother trying to break it free; Red 271 is rated for about 3,000 psi of shear strength.

Break out your propane or acetylene torch. If you're using acetylene, you need little more than a smoky, yellow "starter" flame to heat the Loctite to its 550-degree-Fahrenheit melting temperature. The yellow starter flame provides more than enough heat to do the job.

Apply heat to the bolt head or stud with your torch, just touching the metal with the end of your flame. The trick here is to keep the torch moving around the bolt or stud to evenly heat it, and not to get in a hurry. It's best to avoid heating the bolt up any more than necessary, and to give the heat a little time to work its way down through the metal and to the Loctite. Some like to heat the bolt to a dull red to be sure, but that's a bit overkill.

With the bolt still hot, extinguish your flame and immediately fit the proper socket or wrench with a long breaker bar attached. Apply steady pressure, and the bolt should come free with little more than the amount of torque it was originally tightened to."

[max]

http://www.zerofast.com/proper-bolt-torque


Explains it better than I can

That article's conclusion is the same as how I was trying to, maybe badly, articulate my understanding, so looks like we're in agreement after all!

... https://www.bmw2002faq.com/articles.html/technical-articles/engine-and-drivetrain/installing-exhaust-manifold-or-header-studs-r30/
...

... BMW says finger tight ...

Just for clarification, I'm not sure that article is written or endorsed by BMW in any way? "Collinster742002" seems to just be an enthusiast like us all posting this "John Aho"'s article. I take anything online with a pinch of salt so was just wondering whether there was a source reference behind this as I couldn't find one.



Re loctite, the main controversy is the fact that even the "high temperature resistance" LOCTITE 272 still only has an upper service temperature of 200^oC. Its technical data sheet also claims only needing to heat the fastener to 250^oC for disassembly. Both of these temperatures are much lower than the exhaust manifold can reach which brings into question whether the thread locker will be doing its job or just burn.

However, I like the idea suggested in John Aho's article of using Loctite for "just one drop on each clean, dry, new stud", and hand screwing in the studs, then allowing it to set before tightening the nuts. This should stop the stud from rotating as the nut is tightened.

[MaxD]

Max, with the issue of whether the Loctite even works for this application on the table, I ran an experiment on the temperature.  I used a DMM with a temp probe to find these temperatures on the header bolt and collar:

After 2 minute of idling: 168degC / 336 degF
After 5 minutes of idling: 203 degC / 396 degF
Then 10 minutes of riding, hop off and measure while idling: 202degC / 394degF

The data sheets I have for both Loctite 271 and 272 say a service range of up to 149 degC / 300degF.  But, they also say the removal temp is 250 degC/ 482F. 

So, it seems that after the temp settles we're typically a little over 200 degC and are out of spec on the high temp Loctite.  But, we're still about 45 deg C below the removal temp.  We seem to be in a gray zone where it is sort of working, probably relaxing and then re-hardening every time we run the bike.   

[MaxD]

We have these other options instead of the marginal 271/272:

https://www.lawsonproducts.com/lawson/246-High-Temp-Medium-Strength-Blue-Threadlocker/1383604.lp
Loctite 246 medium strength to 450 deg F (we're at about 400 degF)

https://www.lawsonproducts.com/Loctite/2422-Ultra-High-Temp-Blue-Threadlocker/1383606.lp
Loctite 2422 medium strength ultra-high temp to 650 deg F (might be pretty hard to ever get off)

[Endopotential]

Wow, this thread has definitely wandered off from general maintenance, to a graduate level discourse on studs and Loctite!

Still fun and learning a ton regardless 

[MaxD]

Endo, sorry for it to get so long.  That's happened because Sledge reported this header bolt severe corrosion problem as probably the most serious design flaw on the GS500, but one that should be correctable with stainless steel or chromed hardware.  He's an expert and I believe him.  But, then it gets deep because we have galvanic corrosion material choice issues because the cylinder head is aluminum and does not really match up with anything, there are different grades of stainless steel to be aware of, the decision as to whether to use bolts or studs/nuts, the decision as to whether to use Loctite or anti-seize (hotly contested among experts), the decision on how much torque to use for each of studs and bolts with nothing, Loctite, or anti-seize (can cause over torquing since you don't really know how much to back off on the torque spec), and then finally the fact that the common 271 grade Loctite does not apparently meet the temperature range needed (good to 300F with us at a little over 400F), and the much less available 450F Loctite 246 being expensive and carcinogenic. 

I've ordered a set of SS studs, but am still not sure if that's the best decision or what grade of Loctite (or nothing or anti-seize) to use.  If I use available high temp Loctite 271, it's apparently loosening every time the bike is ridden.  I don't know how many cycles it can go through before it's ruined and effectively does nothing, so that when the header nuts are periodically tightened it may end up over-torquing the studs in because they are moving also (that would tend to happen with anti-sieze also), which can damage the fragile aluminum threads in the cylinder.

It seems like a simple problem, but really is not.  Allow corrosion, bolt breaks.  Too tight and may strip threads.  Too loose and may burn an exhaust valve.  Expensive repairs in each case. 

It's making me wonder if the safest thing is to go back to stainless steel bolts, nothing on them to avoid over-torquing them, and just periodically loosen them to break corrosion and then re-torque them to spec.   At least then I know what I'm putting on those aluminum threads, unless the aluminum to stainless steel galvanic corrosion is spoiling that!  It then leads to thinking again about anti-seize, which may be more consistent for torque than corrosion even though different sources report the need to reduce torque for given clamping by a loose and undependable range of 25% to 50% when using anti-seize.   

[max]

Those temperatures are interesting, I thought it'd get hotter than that - I love a little experiment. Those Loctites also have better potential, but strangely I can't find a reasonably priced supplier for them in the UK.

When I originally said thread locker and anti-seize on headers were an ongoing controversy that was no joke haha. It's been thought provoking at the very least!