Exhaust Hardware Questions

[da Vinci Dan]

I am trying to take my exhaust back to factory condition (w/o spending $5.50/nut at Porsche Classic). I have sourced new bolts and am confused on the specs for the nuts and washers.

1) Can someone confirm the manifold to cylinder head nuts were locking? Also, were they m4,m6 or m8, plated or steel? Porsche classic has all types listed.

2) Were the all the washers plated or stainless steel?

3) Were the nuts and washers used on the crossover pipe, cat and muffler connections plated non-locking with washers? This is how mine was was put together.

My exhaust has a bypass pipe and current hardware is so corroded I can not tell.

Thanks for all the help - any factory references or pics would be great.

[Harpo]

Exhaust studs & nuts are M8-1.25. Most likely yellow zinc. IMHO I would replace with stainless

[HaroldMHedge]

I agree with Harpo M8x1.25.

The PET can be your friend in matters like these - Porsche Classic Genuine Parts Catalog, Illustrations: 202-00 and 202-05.

1. The heat exchangers connect to the head with 6 ea. M8 nuts non-locking 900-076-064-02 and 6 ea. M8 barrel nuts 999-085-001-02. I believe these were originally plated with cadmium. Yellow zinc has typically replaced cadmium.

2. Washers are not used at the head to heat exchanger, crossover pipe, catalytic converter and muffler connections.

3. The crossover pipe, cat and muffler connections use a M8 lock nut (conical style) 900-910-097-02 revised to 900-910-097-0C.

Instead of yellow zinc plating a number of Pelicans use copper coated nuts for the exhaust system.

[Quicksilver]

Save yourself a world of trouble. Use copper plated lock nuts. There is a reason there are all those posts about how to remove exhaust nuts and what to do after you snap off an exhaust stud.

Also a lot of people have a knee jerk response of "Use stainless" for all sorts of stuff. You do not want to screw a stainless fastener into aluminum. It will cause galvanic corrosion which will damage the aluminum over time.

[ClickClickBoom]

Originally Posted by Quicksilver

Save yourself a world of trouble. Use copper plated lock nuts. There is a reason there are all those posts about how to remove exhaust nuts and what to do after you snap off an exhaust stud.

Also a lot of people have a knee jerk response of "Use stainless" for all sorts of stuff. You do not want to screw a stainless fastener into aluminum. It will cause galvanic corrosion which will damage the aluminum over time.

The stainless solution people have no clue. Stainless has a place, 99% is in other applications, not cars.

[Walt Fricke]

Even better, use the copper plated reduced head 12mm socket M8x1.25 flange nuts (the base of the nut widens out to a 13mm circle). Ditch the barrel nuts. If a stud is too long, a flange too thin, a gasket too thin, the barrel nut can screw so far in that the hex tool will no longer fit in far enough to torque them. With a regular nut, no problem, and (as I recall) a 12mm socket is small enough to fit through the holes in the heat exchanger.

And use some anti-seize.

[Harpo]

Thanks

Originally Posted by ClickClickBoom

The stainless solution people have no clue. Stainless has a place, 99% is in other applications, not cars.

[da Vinci Dan]

I appreciate all the thoughtful and well educated responses. I am going to be a bone head anyway. My goal in taking the exhaust apart was to 1) prevent the continuation of rust I know was happening since the rebuild using old fasteners 6 years ago and 2) take it back to as stock as possible.

I plan on using Cooper lube and removing and re lubing the exhaust every few years. My experience is it is not that bad if you stay on top of it with an OCD maintenance excuse.

IMO the original stock exhaust with the stainless exchangers, black crossover/visible pipes with cadmium plated nuts and bolts was just so beautiful.

If anyone has pics of a factory correct restored 3.2 or factory pics of the original engine, I would greatly appreciate it. I have a few still shots from youtubery videos and some Peterson Museum pics of turbos top ends. However, I am still looking for more info. Thanks to all!

[ClickClickBoom]

Originally Posted by Harpo

Thanks

You are welcome, stainless steel is for spoons and forks. A few other applications far away from cars. Research dissimilar metal corrosion, I have and that's where my perspective comes from. Simply uttering a concept keeps it alive. Follow the science.
I had a customer who thought that using stainless screws would "fix" the corroding screw "problem" Turns out from one Annual Inspection to the next year the steel corroded the nutplates and aluminum to the point of they tore out of the aluminum and repairs had to be fabricated. I fabbed 8 or 9, inspection hole repairs in the wing and fuselage. The plating on the fastener is intended to be sacrificial, saving the fastener. If the plating is gone, replace the fastener, because the system is consumed and therefore compromised. All because he thought he was solving for a problem, he solved the corroding screw problem, by sacrificing his planes airframe. The Periodic Table of Elements is your friend.

[ClickClickBoom]

Originally Posted by da Vinci Dan

I appreciate all the thoughtful and well educated responses. I am going to be a bone head anyway. My goal in taking the exhaust apart was to 1) prevent the continuation of rust I know was happening since the rebuild using old fasteners 6 years ago and 2) take it back to as stock as possible.

I plan on using Cooper lube and removing and re lubing the exhaust every few years. My experience is it is not that bad if you stay on top of it with an OCD maintenance excuse.

IMO the original stock exhaust with the stainless exchangers, black crossover/visible pipes with cadmium plated nuts and bolts was just so beautiful.

If anyone has pics of a factory correct restored 3.2 or factory pics of the original engine, I would greatly appreciate it. I have a few still shots from youtubery videos and some Peterson Museum pics of turbos top ends. However, I am still looking for more info. Thanks to all!

The stuff to use is Nickle Anti-Seize:
https://www.permatex.com/products/lubricants/specialty-lubricants-anti-seize/permatex-nickel-anti-seize-lubricant/?locale=en_us
I have all 3 types of anti-seize. Chemicals can make one's life easier. Not just ETOH

[ClickClickBoom]

Originally Posted by da Vinci Dan

I appreciate all the thoughtful and well educated responses. I am going to be a bone head anyway. My goal in taking the exhaust apart was to 1) prevent the continuation of rust I know was happening since the rebuild using old fasteners 6 years ago and 2) take it back to as stock as possible.

I plan on using Cooper lube and removing and re lubing the exhaust every few years. My experience is it is not that bad if you stay on top of it with an OCD maintenance excuse.

IMO the original stock exhaust with the stainless exchangers, black crossover/visible pipes with cadmium plated nuts and bolts was just so beautiful.

If anyone has pics of a factory correct restored 3.2 or factory pics of the original engine, I would greatly appreciate it. I have a few still shots from youtubery videos and some Peterson Museum pics of turbos top ends. However, I am still looking for more info. Thanks to all!

While not stock, it's just cool.......

The only stainless steel hardware is the 4 nuts and bolts holding the muffler to the SSIs.

[Harpo]

I'm familiar with stainless and aluminum in wet environments. In high heat applications we use stainless due to it's ability to retain clamp load over many heat cycles.

Originally Posted by ClickClickBoom

You are welcome, stainless steel is for spoons and forks. A few other applications far away from cars. Research dissimilar metal corrosion, I have and that's where my perspective comes from. Simply uttering a concept keeps it alive. Follow the science.
I had a customer who thought that using stainless screws would "fix" the corroding screw "problem" Turns out from one Annual Inspection to the next year the steel corroded the nutplates and aluminum to the point of they tore out of the aluminum and repairs had to be fabricated. I fabbed 8 or 9, inspection hole repairs in the wing and fuselage. The plating on the fastener is intended to be sacrificial, saving the fastener. If the plating is gone, replace the fastener, because the system is consumed and therefore compromised. All because he thought he was solving for a problem, he solved the corroding screw problem, by sacrificing his planes airframe. The Periodic Table of Elements is your friend.

[famoroso]

I have an M&K 321 Stainless Steel pre-muffler & muffler ready to install on a 1987 3.2 (now a 3.4) with stock heat exchangers and crossover pipes.

They came with stainless steel bolts, washers and nuts. I also have standard steel bolts and copper nuts. Additionally, I have Permatex anti-seize, Wurth CU 800 and Castrol Molub-Alloy (i.e. Porsche NR-Optimoly paste).

I was going to go with steel bolts, copper nuts and Optimoly anti-seize (no washers), but after this thread now I'm not so sure.

So what permutation of bolts, nuts, washers and anti-seize do I want?

[da Vinci Dan]

Nuts and bolts were cad plated steel. Permatex does not last more than two years in the Northeast I have had more luck with copper anti-seize but am willing to try the nickel stuff.

[911pcars]

According to this galvanic reaction chart:
https://www.engineersedge.com/galvanic_capatability.htm

Quoting and paraphrasing the web link:

Each metal has an Anodic Index (volts).
1. For harsh environments, such as outdoors, high humidity, and salt environments fall into this category. Typically there should be not more than 0.15 V difference in the “Anodic Index”. For example, gold and silver would have a difference of 0.15V being acceptable

2. For normal environments, such as storage in warehouses or non-temperature and humidity controlled environments. Typically, there should not be more than 0.25 V difference in the “Anodic Index”.

3. For controlled environments, such that are temperature and humidity controlled, 0.50 V can be tolerated. Caution should be maintained when deciding for this application as humidity and temperature do vary from regions.


Aerospace electrical contacts are gold or gold plated for a purpose. Their Anodic Index is 0, an ideal anti-corrosion match in whatever environment they co-exist.



Here’s a typical Porsche example: Steel fasteners in contact with magnesium (engine case, cooling fan, fan housing, early valve covers, gearbox housing, Mg race wheels, etc.). The Anodic Index of steel is 0.85 (1.25 if zinc plated). Mg has a Anodic Index of 1.75.

When plain steel and Mg are in contact, the difference in the Anodic Index is 0.90 (0.85 vs 1.75). Zinc-plated steel vs Magnesium results ina lower difference of 0.50 (1.25 vs 1.75).

Refer to environment conditions 1, 2 or 3 for acceptable range differences. If those materials are in contact in a harsh environment condition (no. 1), where the Anodic Index difference exceeds 0.15 V, corrosion will be faster.

Thus, Mg, a more active element becomes the sacrificial material (Anodic) and it will corrode faster than the less anodic (more cathodic) steel. The Anodic Index differences become less of an issue as the working environment becomes less severe (indoors, low humidity and less salt) and/or as the difference between Anodic Indexes become smaller.

Fortunately, those Porsche parts are typically not directly exposed to atmospheric conditions and usually operate in high temperature and low humidity conditions, usually. Mg. wheels, on the other hand.....

If you love charts:
https://www.google.com/search?q=galvanic+reaction+charts&sxsrf=ALeKk025-zHODf2nyl2OJY861awij1aM6A:1601100346781&tbm=isch&source=iu&ictx=1&fir=Q0X2JlN3mfR-4M%252C98IahBuavrFJbM%252C_&vet=1&usg=AI4_-kR45eMXbWGITAiaWl7LBfa3beAv1Q&sa=X&ved=2ahUKEwiaoa3Lk4bsAhXYrJ4KHQZAAgwQ9QF6BAgKEEc#i mgrc=Q0X2JlN3mfR-4M

As for protective films that help reduce the contact surface of assembled parts; Dielectric grease as well as anti-seize compounds. Look it up for proper use.

Sherwood

[ChrisHoover]

The galvanic corrosion chart is very helpful. I'll reference it when choosing fasteners. After watching a ton of plating and rust removal videos anode and cathode are clear to me.

Here is another link for folks who filter google

https://www.monarchmetal.com/wp-content/uploads/Galvanic-Corrosion_2.png

[famoroso]

This is what I went with this past weekend for my M&K Active Exhaust pre-muffler and single in / out muffler install (ignore the SS nuts & bolts on the left, I was harvesting the SS washers from them)...



I figure, the SS washers were ok to use adjacent to the SS M&K components.

Also, the Optimoly HT paste is good to 2,012 degrees F. From the MSDS... "For screw connections and other connections in the high temperature range up to +1100°C/+2012°F."

I haven't tightened down the hardware yet tho, Walt, where can I source the copper plated reduced head 12mm socket M8x1.25 flange nuts, where the base of the nut widens out to a 13mm circle, that you referred to? Got part number?

[1979-930]

I installed steel Time-Serts for all the exhaust studs to be done with it. Half broke off on disassembly anyway.

[GH85Carrera]

Originally Posted by ClickClickBoom

The stainless solution people have no clue. Stainless has a place, 99% is in other applications, not cars.

Stainless Steel heat exchangers and mufflers are great. Now Porsche even sells Titanium exhaust systems in the really high end cars.

As I recall the stock muffler on a G body 911 is stainless steel. My muffler is 35 years old with 176,000 miles and looks and works great.

My El Camino has a lot of Stainless trim parts, they look great and no rust after 371,000 miles.

But yea, stainless steel studs in the heads is not a good idea.

[Walt Fricke]

Frank - these aren't Porsche parts. My Buckley headers came with them. Made installation easier - saved weight (though insignificant) too. Who knows - if you replaced every 13mm nut and washer on an engine and transmission with a flange nut maybe you'd save a whole pound? Start your search with flange nuts. I usually start with Maryland Metric, but there are quite a few hardware sellers.

I'm pretty sure Porsche has used copper coated non-flange nuts, maybe 8mm thread but 12mm wrench, for some purposes, like holding carburetor manifolds or other manifolds to heads. The ones I am thinking of have a horizontal slit, which serves to reduce the tendency of a slightly loose nut to back off farther. These, too, have copper coating (or whatnot - one just sees the surface color, and I don't have personal knowledge of what is coating and what is not, but tend to believe those who say it is a coating).