Galvanic corrosion ?

commandofastback

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Nov 29, 2004
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After reading the exhaust nut thread and watching Jims heat expansion tests, i ordered a set of aluminium exhaust nuts from Andy Molnar now.
Aluminium in Aluminium is prone to seize and Andy states that the nuts should be inserted with copper anti seize.
I am somewhat unhappy with the though of using copper on aluminium because as far as i know the copper would act as a cathode and the aluminium as an anode.
Meaning the copper would eat the aluminium and maybe ruin the threads.

On the other hand, the galvanic corrosion also needs an electrolyte to work between the two metals.

... and lots of people use a blob of copper paste on the spark plug threads.

The galvanic potential difference between Nickel and Aluminium is even higher.
Zinc would be the other way round (Aluminium would be the cathode and Zinc the Anode)
In the end i will go for ceramic antiseize now.

Whats your opinion ?
Or am i just a natural worrier ? ;)
 
Nothing wrong with doing it right now to keep from having to fix your repair later.
Good call on the ceramic based anti-seize.
 
I Used copper grease on the (steel) exhaust nuts for the last 40 odd years, never seen a sign of corrosion on the alu cylinder head.
 
I use copper high temp Permatex Silicone on the threads and have never had a back-off this way . Stuff's amazing , we smear it all over our pancakes in the morning before a ride . I can't see copper being any sort of problem re : galvanic corrosion . I have seen aluminum magically start to degrade into thin air using nothing . ( Usually evidenced with barn finds or outdoor abandoned vehicles ) . Enjoy .
 
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Aluminum, copper, saltwater and add a little electricity, now that is were you would have problems and you can't use cooper coat antifoul on alloy boats.
 
ashman said:
Aluminum, copper, saltwater and add a little electricity, now that is were you would have problems and you can't use cooper coat antifoul on alloy boats.
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Just reading about it on the internetty thingy . Dissimilar metals connecting bad . Insulating from them good . Grease , anything , copper silicone , blood , cheese ( French of course ) to prevent direct contact . Electrically .. good grounds , failing that , how about a ground strap from the rear flapping to the pavement . Anyone remember ground straps ? Or chains ?
 
Torontonian said:
I use copper high temp Permatex Silicone on the threads and have never had a back-off this way . Stuff's amazing , we smear it all over our pancakes in the morning before a ride . I can't see copper being any sort of problem re : galvanic corrosion . I have seen aluminum magically start to degrade into thin air using nothing . ( Usually evidenced with barn finds or outdoor abandoned vehicles ) . Enjoy .
Click to expand...
Collectors of old german model trains from the 1920s know a phenomenon called "zinc pest". Turned out that, because of the metal shortages after WW1, they used a zinc alloy that was contaminated with other metals. Those parts simply deteriorate to dust. It also happens to some old BING carburettors made of pot metal.
 
Torontonian said:
Just reading about it on the internetty thingy . Dissimilar metals connecting bad . Insulating from them good . Grease , anything , copper silicone , blood , cheese ( French of course ) to prevent direct contact . Electrically .. good grounds , failing that , how about a ground strap from the rear flapping to the pavement . Anyone remember ground straps ? Or chains ?
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I think I still have an unused rubber one somewhere.
 
They became popular when women's dresses and slacks were made of man made materials (remember crimplene) and seats were man made velour. Lots of static which earthed with a crack when you exit the Farraday cage. I remember, when I was a child, rubbing my hair in my dad's crimplene safari jacket, to make my hair stand on end :D
 
This is all good, provided there's a potential difference between the cylinder head and exhaust.

I was told that using stainless fasteners would cause galvanic corrosion with the crankcases.
40 years later I'm still not seeing those symptoms.
 
commandofastback said:
Collectors of old german model trains from the 1920s know a phenomenon called "zinc pest". Turned out that, because of the metal shortages after WW1, they used a zinc alloy that was contaminated with other metals. Those parts simply deteriorate to dust. It also happens to some old BING carburettors made of pot metal.
Click to expand...
An old Bing carb from my old NSU Quickly turned to dust after many years left in the garage
 
I use nickel anti-seize rather than copper everywhere for three reasons.
1) It is higher temp.
2) Considered better than Copper for Stainless Steel.
3) It is much closer in color to the metals in our bikes.

For exhaust nuts, it only takes (and you should only use) and tiny amount. You can tighten the about 1/4-1/2 turn more with the anti-seize.
 
Aluminium nuts? I wouldn't do that. Just because I wouldn't do that. They are cheap, and they are light. But, does the weight saving add up to much?

What I have done is used stainless nuts from Pat Seager. And I just bought a second set. Really, they aren't heavy. See below link. Scroll down for a lot of Commando stuff. What they aren't is cheap.

And I still tend to put on a bit of copper anti seize, mainly because the nuts are sometimes hard to start. Rigid mounted engine and fairly rigid mounted exhaust impacts that, Commando should be easier,


1706457147487.jpeg
 
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Lineslinger said:
Nice fabrication on the pipes.
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Nigel Parker, NRP Exhausts, Bilsthorpe, Nottingham, UK. Good race performance.

Thinking about having a 'noisy' exhaust made by Raysons! Traditional sand bent pipes. But probably a project too far! Too many other things to do, too little budget!

Galvanic corrosion ?
 
ashman said:
Aluminum, copper, saltwater and add a little electricity, now that is were you would have problems and you can't use cooper coat antifoul on alloy boats.
Click to expand...
Yes, the missing piece in the commando head scenario would be the electrolyte (any fluid capable of carrying charged particles). In marine scenarios, lumps of zinc alloy are bolted to outboard engines near the propeller to act as sacrificial anodes. Over months or yrs they need replacing as they corrode away...but only if left in the water. This does not happen at any noticeable rate out of the water.

So copper slip on alu into alu threads should not be a corrosion issue for our heads.
 
Copper is the main alloying element in higher strength aluminium, where it is about 4%. Those alloys cannot usually be anodised successfully. Marine auminium usually has magnesium as the main alloying element. 6000 and 7000 series aluminium have a bit of everything. Your aluminium cylinder head is probably high in silicon to get the casting properties. - I suggest any galvanic effect from a copper insert in aluminium in a motorcycle cylinder head would be very minor. The difference in expansion rates might be more important. But copper might deform better to stay put where it belongs.
 
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