Exhaust manifold nuts

[EricH]

While separating the downpipe from the exhaust manifold, I twisted off one of the manifold studs.:sigh: So now I get to pull the manifold too, so that I can get what's left of the stud out of it. :sigh: :sigh:

Of course this only happens because the nut is be frozen to the stud so they won't separate, AND the stud is be frozen to the manifold so that it breaks instead of unscrewing. There's got be a better choice of hardware for this application than ordinary steel nuts torqued onto ordinary steel studs set into the cast-iron manifold. What I should I use when I go to reinstall the downpipe on the manifold?

 

[haywood j]

I drilled my broken studs out and replaced with nuts and bolts

 

[TonyK]

Well there are a few choices.

My 79 I have had apart so many times that the nuts always come free. But, as time went on I always coated the threads of the stud with Never Seize compound. On many of the USA vehicles steel studs with brass nuts were the OEM choice. When I rebuilt my 87 Exhaust system I used stainless bolts and nuts but coated with anti-seize compound. Don't waste your time with stainless studs in a manifold unless you use the anti-seize compound, Stainless is softer and will shear off easier than Steel studs.

My 87 had 1 broken stud and 2 that were rusted and then stripped so I had to remove the lot. I did it on the car from the trunk. It took me 3 hours to do it.

The problem isn't what you are replacing it with, but what was done from the factory or other repairs and no one coated the threads for the next guy. Do the next guy and yourself a favor, coat the threads and know if you ever have to remove a nut or stud again on this car you CAN!

TonyK

Grimsby Ontario Canada.

 

[///Mike]

The problem isn't what you are replacing it with, but what was done from the factory or other repairs and no one coated the threads for the next guy. Do the next guy and yourself a favor, coat the threads and know if you ever have to remove a nut or stud again on this car you CAN!

Spot on Tony. Excellent advice.

For what it's worth, BMW uses copper nuts with integral washers that are slightly ovaled when new so as to provide a bit of locking. Think I'm going to use these along with stainless studs, combined with some high quality anti-seize.

///Mike

 

[Chris Obert]

While separating the downpipe from the exhaust manifold, I twisted off one of the manifold studs.:sigh: So now I get to pull the manifold too, so that I can get what's left of the stud out of it. :sigh: :sigh:

Of course this only happens because the nut is be frozen to the stud so they won't separate, AND the stud is be frozen to the manifold so that it breaks instead of unscrewing. There's got be a better choice of hardware for this application than ordinary steel nuts torqued onto ordinary steel studs set into the cast-iron manifold. What I should I use when I go to reinstall the downpipe on the manifold?

I always just use the standard hardware, but I double nut every exhaust thread. And when it comes to removing them, my first tool grabbed is the heat wrench.

 

[Rupunzell]

One thing I simply do not like or tolerate is frozen or rusty exhaust hardware. To deal with this, I used M8 studs from ARP which is made of A286, a high temp stainless steel alloy designed with a service temperature of 900 degrees F along with matching M8 ARP nuts. The exhaust flanges are held together with 5/16" dia bolts and nuts made of Inconel 718 (more aerospace hwd), another stainless steel alloy designed for high temperatures. This hardware simply works.

It should be noted that conventional steel hardware should have a service temperature limit of 450 degrees F.

Those copper plated self locking nuts common on a number of European cars today work quite well.

And, SAAB used an interesting solution to the large temperature changes experienced on turbo engines. They use a long spacer and stud that expands with temperature to take up the dimension differences due to expansion / contraction with exhaust manifold temperature. It works, the hardware stays in place and the parts don't rust stuck on.

While separating the downpipe from the exhaust manifold, I twisted off one of the manifold studs.:sigh: So now I get to pull the manifold too, so that I can get what's left of the stud out of it. :sigh: :sigh:

Of course this only happens because the nut is be frozen to the stud so they won't separate, AND the stud is be frozen to the manifold so that it breaks instead of unscrewing. There's got be a better choice of hardware for this application than ordinary steel nuts torqued onto ordinary steel studs set into the cast-iron manifold. What I should I use when I go to reinstall the downpipe on the manifold?

 

[bbrown]

I'm using a brass nut that

mimics the original steel nut. Not sure the durability but at least they won't rust.

 

[Rupunzell]

It may surprise you

Brass nuts on the exhaust is a very reasonable choice. This has been done a piston engine aircraft engines in the past and some still use brass nuts on the exhaust to this day. Those nuts look to be about three thread diameters long which should be plenty strong.. and the durability might surprise you.

Problem with commercial stainless steel screws, most every one of them I have seen in recent years have thread finish that is close to a saw blade than a properly finished thread. This finish causes the threads to lock up when assembled better than Loctite green (RC609). Using anti-seize helps, but does not always fix this problem, heat makes the problem far worst. They are generally made of 303/304 SST with a tensile strength of 75Ksi or about 60% of a Grade 8.8 bolt.

Seems like screw producers in Asia and elsewhere don't understand how to roll threads properly and are focused on cost reduction and cheap parts.

It's all part of cost cutting of just about everything made these days... I have been told some commercial, industrial screw/bolt/nut manufactures just break even on selling what they produce and a good part of the profits come from selling the metal scraps that come from production.

This is why I stay away from most commercial stainless steel hardware these days. Heck, I strongly avoid any commercial hardware in the shop unless it's metric.

Back in the 1990's there was a number of aircraft commercial and military including the Space Shuttle that got caught with imitation aero spec hardware (early China, US of A garage shoppe, Taiwan and etc). It's no laughing matter if there is a fastener failure on aircraft or any space craft. This little episode cost NASA (tax payers) many millions of dollars to remove and replace all the imitation hardware on the Shuttle alone. The imitation suppliers were forced out of business and incoming inspection and source inspection of this stuff got a lot tighter.

mimics the original steel nut. Not sure the durability but at least they won't rust.

 

[///Mike]

Bernice...

Do you recall the lengths of the ARP studs you used?

Got a good source for Inconel fasteners in small quantities?

I've always thought of exhaust work as like plumbing repairs-- just about everything you touch needs to be replaced. Unless it was good stuff to begin with, that is.

///Mike.

 

[Rupunzell]

Hello Mike,

It been a while since that engine was put together, if I did some digging it's possible to find the ARP invoice for the studs and nuts. It would be easier to measure the studs and order the lengths required. If the stock exhaust manifold is used, the long center exhaust manifold stud might not be available from ARP. They are all M8 x 1.25. Here is a link to ARP, look at page 75.
http://www.arp-bolts.com/Catalog/Catalog.html

As for Inconel hardware, these are not easy to obtain unless you're near what once was Boeing's surplus or So Cal or other places where there is a good amount of aero surplus available. Every so often this stuff appears on evil-bay. I purchase this stuff when available and squirrel it away in shop stock.

There are a number of aircraft hardware suppliers on line such as Coast Fab:
http://www.coastfab.com/

Genuine Aircraft Hardware:
http://www.gen-aircraft-hardware.com/

And many others... The cost might be a problem.

Of the A286 bolts that are some what common surplus, it would be the NAS1003 to NAS1020 series. This part has been around for a long time and shows up often enough surplus. Use this drawing as a guide to what might fit your needs.

Note 4 on sheet 2, shows a call out for this bolt to operate to 1200 degrees F.







Here is what a NAS1005 bolt and matching A286 silver plated nut looks like. The other bolt is a Boeing spec part (B30UU5)made of Inconel 718. Note the smooth, ground finish on the bolt's grip length.


Put these on the exhaust system and they won't rust, seize on, break off unless improperly sized or installed and makes the exhaust system easily serviceable for a very, very long time.

Keep in mind Bob's suggestion of using brass nuts is a good and very reasonable one and in many ways easier to do than source and modify the metric threads to inch standard which is what most aero spec hardware is.

Do you recall the lengths of the ARP studs you used?

Got a good source for Inconel fasteners in small quantities?

I've always thought of exhaust work as like plumbing repairs-- just about everything you touch needs to be replaced. Unless it was good stuff to begin with, that is.

///Mike.