Is there a checmical reaction betweel brass and iron? - PeachParts Mercedes-Benz Forum

strelnik · #1 03-27-2010, 05:02 PM

I am cleaning up the 220D of 1973 vintage and I have not yet pulled off the nuts holding the exhaust manifold to the motor.

My plan is to remove and clean up this manifold, even paint it, because the surface looks so god awful rusty and ugly.

I replaced the bolts holding the head pipe to the exhaust manifold and didn't need heat to do it, just some penetrating oil.

I have replaced the head pipe to manifold fasteners with stainless steel nuts and bolts. Am letting the oil soak a day before I try anything else on the studs on the engine block that are holding the exhaust manifold.

But this made me think: What about brass nuts on the studs?

A while ago I got a 1951 Citroen Traction that had the original nuts on the exhaust manifold. They are very unique-looking and BRASS, which is how I know they are original. I was able to take them off with just abit of coaxing with a propane blowtorch, I didn't need MAPP gas or acetylene.

That makes me wonder: Is there a chemical reaction between brass and iron? I know Citroen used brass bolts in certain areas of the car and a lot of them on non-engine parts near coastal areas because they were easier to use before stainless steel, and more available.

Anyone know anything about how brass nuts would fare on a MB 220D exhaust? I might make some brass nuts for the 240D if it prevents shearing off the studs, that's why I would do it.

Thanks

Brian Carlton · #2 03-27-2010, 05:13 PM

There won't be much, if any, of a chemical reaction between brass and steel. The brass, being an alloy of copper, is fairly inert. Although, it has been mentioned that copper fittings should not be used in conjunction with iron pipe on domestic heating systems if you want the system to last forever.

The only drawback that I can see is the available torque. Brass is very soft and won't take much torque...........might be OK........might not.

strelnik · #3 03-27-2010, 05:41 PM

Quote:

Originally Posted by Brian Carlton

There won't be much, if any, of a chemical reaction between brass and steel. The brass, being an alloy of copper, is fairly inert. Although, it has been mentioned that copper fittings should not be used in conjunction with iron pipe on domestic heating systems if you want the system to last forever.

The only drawback that I can see is the available torque. Brass is very soft and won't take much torque...........might be OK........might not.

Thanks. The torque on the Traction exhausts is about 45 lbs-ft. I can see not using the brass to hold cylinder heads in place, am just thing of the convenience thing.

Maybe I need to go hunting for stainless steel nuts and bolts in popular sizes.

Brian Carlton · #4 03-27-2010, 06:28 PM

Quote:

Originally Posted by strelnik

Maybe I need to go hunting for stainless steel nuts and bolts in popular sizes.

Don't do it.

Stainless is usually very soft and has a miserable tendency to seize onto the mating threads.

I've had two stainless fittings seize to the point where no amount of force would break them loose. Even a torch couldn't break the bond.

my83300cd · #5 03-27-2010, 06:30 PM

When I replaced the muffler on my VW I used copper nuts.
8 months later I developed an exhaust leak from one of the exhaust pipes and had to take it all apart- no problem with the copper nuts at all. Maybe the anti-sieze on the studs helped.

strelnik · #6 03-27-2010, 06:37 PM

Quote:

Originally Posted by my83300cd

When I replaced the muffler on my VW I used copper nuts.
8 months later I developed an exhaust leak from one of the exhaust pipes and had to take it all apart- no problem with the copper nuts at all. Maybe the anti-sieze on the studs helped.

Good to know-- did you make or buy the copper nuts?

JEBalles · #7 03-27-2010, 06:40 PM

Couldn't you just put some anti-seize on the steel nuts and threads?

smiffy6four · #8 03-27-2010, 06:48 PM

I've seen and used brass nuts for exhausts on lots of vintage cars over the years. Works for me. :-)

layback40 · #9 03-27-2010, 07:02 PM

X2 with Brian on the stainless. Putting stainless nuts on steel studs is a guarantee of a seizure.
Brass nuts were very common on exhaust manifolds and flanges of English cars in the 1950's & 60's. They were generally UNF, I have never seen a UNC or Witworth thread in a brass nut. That maybe because of the softness of the brass, its still stronger than copper. If you can get them, they are good on exhaust applications.

strelnik · #10 03-27-2010, 07:56 PM

Quote:

Originally Posted by layback40

X2 with Brian on the stainless. Putting stainless nuts on steel studs is a guarantee of a seizure.
Brass nuts were very common on exhaust manifolds and flanges of English cars in the 1950's & 60's. They were generally UNF, I have never seen a UNC or Witworth thread in a brass nut. That maybe because of the softness of the brass, its still stronger than copper. If you can get them, they are good on exhaust applications.

Thanks for the info, I have a lathe, I'll buy brass hex stock and make them!

vstech · #11 03-27-2010, 10:58 PM

what about bronze? would it be stronger than brass? and would there be a diff between yellow and red brass?
I had some alt spacers modded out of bronze for me, I'm sure I could get nuts done.
and Yeah, SS and Iron don't play well together.
you could get SS studs made to replace the iron ones, but then the head would lock onto the SS stud, and if you ever broke one, you'd be SOL...

Rudolf_Diesel · #12 03-27-2010, 11:16 PM

SS studs and nuts do not play well together, but I have used SS studs/bolts with brass nuts for exhaust and that combo works well. Even on non heat cycling applications, SS has a tendency to gall up and sieze.

barry123400 · #13 03-28-2010, 12:11 AM

For the members that do not have a set of torches. A cheap set of nutcrackers/splitters from harbour freight even will last you a lifetime for occassional use. I figure less than ten dollars in the states for a cheap set.

If there is room to get them around a nut once split it will remove easily and the threads of the stud or bolt are undamaged. Some nuts will remain very difficult even with real heat on occassion. Or if you round them off you can still split them.

Up here in the rustbelt with no serious heat on site you can not do a lot of jobs. Or it is just too painful to attempt otherwise. So we tend to use a combination of aproaches.

Diesel911 · #14 03-28-2010, 12:40 AM

Quote:

Originally Posted by JEBalles

Couldn't you just put some anti-seize on the steel nuts and threads?

X2 on the above. I would use anti-seize on the exhaust Nuts/Bolts/Studs no matter what metal you plan to mate togethet.

Lycoming-8 · #15 03-28-2010, 01:09 AM

As both Brian and Rudolph D have mentioned stainless steels have the very unfortunate metallurgical propensity to Gall which is basically microscopic welding of the threads between nut and bolt or stud. If I remember correctly, the Galling phemenon is even worse at higher temperatures, so exhaust service would not bode well for SS fasteners.

The use of SS and brass would likely work fairly well, but as was already mentioned even the use of brass nuts on plain steel bolts or studs works pretty well. One other thing to think about is the fact that some stainless steels tend to suffer stress corrosion cracking and this is severely enhanced by the presence of chlorides such as winter use salt in the presence of water!!