Corrosion

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mikenixon
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Corrosion

Post #1 by mikenixon » Sat Dec 17, 2016 4:59 pm

Image

Corrosion. Endemic to the GL1000. In fact, this more than anything, even more than broken float pivot stantions, junks a carburetor. Because broken stantions is repairable. Corrosion, in all but the mildest examples, is not.

The GL1000 is susceptible to corrosion not because of ethanol fuel, not because of dissimilar metals, and really for no other reason than its metal. Until the late 1970s, Keihin made all their carburetors with an aluminum alloy that was rich in zinc. Production engineers will tell you when something is made of this alloy it is either for cost reasons (when it is almost all zinc, such as in children's toys of the 1950s), or due to the lack of advanced casting technology. Manufacturers with still-developing casting technology used alloys heavy in zinc because it flowed well into molds. It was easy to cast. Look at 1950s and 1960s BMW carburetors, Triumph carbs, and others.

A few years ago I compared a GL1000 single carb body, stripped to the bare casting, with a similarly prepared GL1100 carburetor. The two are very close in size (though the 1100 has a slightly smaller bore). Guess what? The GL1100 carb casting was lighter, much lighter, than the heavier GL1000 carb body, demonstrating the high zinc content of the GL1000 carburetor. The GL1100 carb alloy appears identical to that used in the DOHC fours, CBX, CX500 and others. Much more aluminum and less zinc.

GL1000 = 2 lbs.
GL1100 = 1 lb.

What does this have to do with corrosion? Just this. Remember what boats have on them? Sacrificial zinc annodes. The annodes take the brunt of electrolytic corrosion, theoretically leaving the other metal in the boat relatively free of corrosion.

So your GL1000 carbs are basically huge sacrificial zinc annodes. A little overstated, pethaps, but not far from the truth. After 40+ years these carbs are showing up very eaten up around their jet towers, as depicted in the image above. For this reason, I keep in stock a number of good replacement bodies for my customer's projects. More information at the links below.

http://www.motorcycleproject.com/text/zinc.html
http://www.motorcycleproject.com/text/c ... epair.html
Last edited by mikenixon on Mon May 14, 2018 11:05 am, edited 1 time in total.
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77Gowing
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Re: Corrosion

Post #2 by 77Gowing » Sun Dec 18, 2016 12:26 pm

another way of stating the difference in weigh of the two materials is to compare their respective densities.

Zinc: 7.140 g/ml
Aluminum: 2.70 g/ml

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mikenixon
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Re: Corrosion

Post #3 by mikenixon » Sun Dec 18, 2016 8:11 pm

77Gowing wrote:another way of stating the difference in weigh of the two materials is to compare their respective densities.

Zinc: 7.140 g/ml
Aluminum: 2.70 g/ml


Hey, yeah! Scientific, that! Visitors to my shop are always amazed when I hand them the two carbs. The difference is startling felt in your own hands.
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Re: Corrosion

Post #4 by 77Gowing » Mon Dec 19, 2016 6:32 pm

[/quote]
Hey, yeah! Scientific, that! Visitors to my shop are always amazed when I hand them the two carbs. The difference is startling felt in your own hands.[/quote]

For sure, often the best lessons are learned by physically experiencing it like you suggest. Like Dr. Thomas Sowel says in one of his articles titled, "Experience Trumps Brilliance." (trump being used as a commonly used verb in this case)

Mike, I respect your knowledge and your experience. :!: ;)

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Re: Corrosion

Post #5 by mikenixon » Tue Dec 20, 2016 7:54 pm

:)
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salukispeed
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Re: Corrosion

Post #6 by salukispeed » Wed Dec 21, 2016 1:03 pm

I too see the lower portions of so many Zinc carbs . I believe it takes some sort of an electrolyte siting in there such as water to carry on the process. Ones with water in them are destroyed pretty quickly. Does the affinity for moisture of the alcohol blended fuels ad to the water concern if left in unprotected environment. The alcohol is not directly the problem as much as its love of moisture.

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Re: Corrosion

Post #7 by mikenixon » Thu Dec 22, 2016 12:00 pm

salukispeed wrote:I too see the lower portions of so many Zinc carbs . I believe it takes some sort of an electrolyte siting in there such as water to carry on the process. Ones with water in them are destroyed pretty quickly. Does the affinity for moisture of the alcohol blended fuels ad to the water concern if left in unprotected environment. The alcohol is not directly the problem as much as its love of moisture.


Agreed. No doubt ethanol contributes to the issue, but I think it happens nearly as badly apart from the ethanol.
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Re: Corrosion

Post #8 by salukispeed » Thu Dec 22, 2016 12:33 pm

So true. Water is not our friend.

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Re: Corrosion

Post #9 by Toehead » Thu Dec 22, 2016 2:07 pm

I've got a bunch that look like that too.

At least they don't seem to get the zinc pest that the toys used to get :)


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