What is the curent thinking on exhaust stud nuts, Copper or regular? Options

[thomasotten]

Are the copper coated nuts the way to go, or is using regular bolts, double bolting the way. I read something yesterday that said the copper nuts should only be used once...why?? Should I coat the studs with anything?

[Jake Raby]

Those copper nuts are evil.

I throw them away.

Who ever had the idea to use them has obvilusly never had a class on the effects of dissimilar metal corrosion.

This post has been edited by Jake Raby: Oct 10 2007, 11:19 AM

[rhodyguy]

what is the prefered fastener jake?

[914Sixer]

I prefer the factory nut but they are not cheap. Last I heard they were about $8 each.

Has anybody tired the 911 barrel nuts? I know they have an allen head but they have a some meat to them.

[brer]

Copper plated objects are rated differently than pure copper.

copper plated items are nearly in the same location as steel on the galvanic table and as such are excellent match for stock studs.

[URY914]

I've used stainless steel nuts in the past. Problem is they work loose over a short period of time. The stainless doesn't "grip" the stud too well. Sometimes a little rust is a good thing.

[solex]

I switched to SS nuts and washers as the copper lock nuts were pulling out studs

[davep]

Jake has said in the past that he uses stainless steel nuts in pairs (double-nutting). I've seen them on his web-catalog. Pretty cheap if you buy a bag of 25. Then use more for the muffler. I assume they also work well for the HD rocker studs and the regular intake studs, so you can use up a bag or two very quickly.

[Jake Raby]

The double nut trick also keeps rust off the protruded portions of the studs reducing other issues down the road.

Milk of Magnesia and double nutted stainless fasteners are what you'll find on my personal cars.

[thomasotten]

Found these two items in CB:

http://www.cbperformance.com/catalog.asp?ProductID=373

http://www.cbperformance.com/catalog.asp?ProductID=379

[thomasotten]

The double nut trick also keeps rust off the protruded portions of the studs reducing other issues down the road.

Milk of Magnesia and double nutted stainless fasteners are what you'll find on my personal cars.

Jake,

Is that bag of nuts in my kit "stainless steel"?

[brer]

its worth noting that SS nuts on stock studs is pretty much a waste.
they will rust along with the stud.

if you use SS nuts then SS studs would also be a must.

[Jake Raby]

Thats not been my experience.

Milk of Magnesia works wonders.

[URY914]

its worth noting that SS nuts on stock studs is pretty much a waste.
they will rust along with the stud.

if you use SS nuts then SS studs would also be a must.

You're saying a SS nut will rust because it is on a SS stud?

Really? They don't where I live.

Please explain.

[Rand]

its worth noting that SS nuts on stock studs is pretty much a waste.
they will rust along with the stud.

if you use SS nuts then SS studs would also be a must.

You're saying a SS nut will rust because it is on a SS stud?

Really? They don't where I live.

Please explain.

Not what I thought Brer said. Are stock studs stainless?

But I figure some Milk of Magnesia on the threads and double SS nuts is the way to go. The biggest trick is getting a hold of the top nut well enough to tighten the two nuts against each other enough to lock them.

[brer]

ok, in my experience with boats and cars. rust on normal steel will migrate onto Stainless Steel if they are touching. I know because i've put SS nuts onto normal steel bolts and watched it happen.

SS is not impervious to rust.
carbon steel can "contaminate" stainless.


Milk of magnesia I have not tried yet.

[Pat Garvey]

Regardless of the Milk of Magnesia concept (which I would love to hear some rationale too), or the double-stainless nutting thing (which I can sorta undertand), how are torque settings affected by these tchniques?

Pat

[Rand]

The first nut should be torqued properly, then held still while the second nut is tightened against it enough to keep them from moving (as opposed to just reefing on the second nut, which would affect the torque).

[Jake Raby]

The Milk of Magnesia is the worlds best super high temperature anti-seize, I learned the trick from using it on ignitor plugs and exhaust flanges on Turbo haft jet engines. Our exhaust flanges saw temps of over 3,000F for hours at a time.

The most odd part of that was the fact that a stainless steel double locking nut was used on a mild steel bolt for those flanges and they didn't rust or seize into place when the MOM trick was used. I also use MOM on spark plugs. MOM has a high concentration of pure magnesium in it's composition, with it comes a non lubricant based anti-seize that doesn't burn off or go away with time.

Sometimes on test engines we can see EGT of 1400F for hours at a time, and then change exhaust systems as much as 6 times in one day. After you have tried everything in the book to avoid issues when doing this and one thing repeatedly works over and over again you tend to note the trends and give the engine what it wants. There is nothing worse during development than a pesky exhaust system change that takes more than 15 minutes to do, the whole time you are losing the weather and inviting variables- I avoid this at all costs.

There is also a difference in staniless nuits, some are pure stainless (what I use) and others are just stainless coated nuts, with temperature these will rust.

The double nutting keeps the nuts from relaxing on the studs after heat cycles and falling off because of lost torque from heat cycling. The double nuts also keep thread protrusion from occuring where rust will form and then jam between threads when the fastener is attempted to be loosened. If you have ever loosened an exhaust nut, broke torque on it and then it got tighter you have experienced the effects of crusty threads that cause more snapped studs than anything else combined.

The second nut serves dual purpose as a loking device for the primary nut as well as avoiding thread protrusion, resulting in nice clean threads that are easy to remove years later.

The 911 nuts also avoid thread protrusion with their design.

Remember, at the port exit (flange) temperatures stay over 1000F most all the time with spikes to over 1200F on most all engines daily. That heat will cause issues over time if given the opportunity.

BTW- I have tried full stainless studs in this area coupled to stainless nuts. What was the result? The studs EXPLODED as soon as the car got 3 laps under it's belt and the exhaust system damn near fell off on the track before we could get it back to the pits.

So, whats the significance of this picture? This is a picture of the missing fence bolt that I robbed at the track in July when during a test day with the FP car a stainless steel flange bolt that Len used to fasten the stub pipe to the header also exploded. I robbed this crappy galvanized grade two bolt from the fence along with it's nut and we finished our test work. Len came off the track, we heard a small metallic pop and looked under the car to find the bolt and the nut shattered in 3 pieces laying under the car.


Improvise, Adapt and Overcome.

[Cap'n Krusty]

There's an interesting article on stainless steel hardware (and it's appropriate uses) in last month's issue of Motor Magazine. Non-geek that I am, I dunno how to get you the pages from the PDF, so I'll give you a link. Once you have the PDF, go to page 26. Perhaps we can end this clueless insistence on the use of SS hardware. Here's the link: http://ct.emeraldmail-usa.com/rd/cts?d=7-1...25-0-0-0-1-2-23

BTW, the factory used one kind of exhaust nut on the 1.7/1.8s, and another on 2.0 cars. BOTH were steel with a SS insert. A Helicoil, or whatever brand they use in Germany. I save and reuse them as often as I can, as they work just fine unless/until they get rounded off. They are the best thing I've found to maintain the torque in the hot/cold environment of the exhaust system. I also paint the studs with anti-seize.

Maybe someone can get the contents of the article into an e-mail so we'll have it here for all to see.

The Cap'n