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Old 09-07-10, 03:40 PM   #1
RiverHills
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Mixing steel chainring bolts with alu chainrings...

I needed a new set of chainring bolts for my standard Sram Force crankset. Local shop only had chrome plated steel bolts, which was fine with me since standard alu chainring bolts tend to strip easily.

However, I'm concerned about contact corrosion (or galvanic reaction) between the two dissimilar metals. Does anyone have experience using steel bolts with aluminum chainrings?
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Old 09-07-10, 03:50 PM   #2
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I think steel bolts with alu rings is basically standard for most cranks so should not be a problem. As always, grease or anti-seize compound on the threads and contact areas is a good idea.
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Old 09-07-10, 03:54 PM   #3
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Agreed - it will be fine as long as you use an anti-seize compound (available at any auto parts store).

-Sam
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Old 09-07-10, 03:57 PM   #4
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Agreed - it will be fine as long as you use an anti-seize compound (available at any auto parts store).

-Sam
I did put anti-seize on the threads, but that's not what I'm worried about. I'm worried about the interface where the outside of the steel bolts contact the aluminum chainrings.

And btw, the bolts that came with my crank where aluminum.
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Old 09-07-10, 04:02 PM   #5
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the bolts usually get some form of protective coating, like chroming, that keep it from rusting.
actually, the part that will rust first in a chainring bolt, is the spot where the tool comes in contact with the bolt.
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Old 09-07-10, 05:19 PM   #6
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the bolts usually get some form of protective coating, like chroming, that keep it from rusting.
actually, the part that will rust first in a chainring bolt, is the spot where the tool comes in contact with the bolt.
+1
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Old 09-07-10, 07:30 PM   #7
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Galvanic corrosion also requires the two dissimilar metals to be immersed in an electrolyte, like saltwater. For typical cycling environments. I wouldn't worry about it.
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Old 09-07-10, 08:02 PM   #8
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Every crank I've ever worked on, including models from Shimano, SR, Sun Tour, Suguino and Campy, have steel bolts and aluminum chainrings. They have never caused any problems even though some of the cranks were in service for 30,000 miles and used in all types of weather.

Do use grease or anti-seize on the bolt threads but don't worry about corrosion between the chainrings and bolts. It's not a problem
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Old 09-07-10, 08:56 PM   #9
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Every crank I've ever worked on, including models from Shimano, SR, Sun Tour, Suguino and Campy, have steel bolts and aluminum chainrings. They have never caused any problems even though some of the cranks were in service for 30,000 miles and used in all types of weather.

Do use grease or anti-seize on the bolt threads but don't worry about corrosion between the chainrings and bolts. It's not a problem
Ditto. It worked for Eddy Merckx- are you better than Eddy? I think not. 8-)

I've had more issues with aluminum chainring bolts not holding torque or stripping out. Steel bolts work fine. I grease the threads on mine.
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Old 09-07-10, 10:49 PM   #10
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You should do some maintainence occasionally , take stuff apart to thoroughly clean it.. at least ..
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Old 09-08-10, 07:36 AM   #11
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+100 Steel bolts and alloy chain rings are pretty much the standard.

On steel bikes, you will have several places where aluminum and steel meet, like the stem and seat post. That's where the corrosion can be a real problem.
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Old 09-08-10, 07:47 AM   #12
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I'm still not convinced. I have seen plenty of rust on drive train components. Even with lubrication and maintenance, that area still collects more than its share of road grime, salty sweat, etc.

There is about 0.30 V of potential between aluminum alloy (anode) and chrome plate steel (cathode). It is not recommended to combine dissimilar metals with greater than 0.25 V difference in "uncontrolled" environments. However, in indoor climate controlled environments, you can get away with as much as 0.50 V. The chainring is probably somewhere between uncontrolled and indoor conditions so perhaps by that criteria 0.30 would be ok. But to me, it's inevitable that the galvanic reaction will occur over time. The questions is how much time.
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Old 09-08-10, 09:02 AM   #13
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I'm still not convinced........But to me, it's inevitable that the galvanic reaction will occur over time. The questions is how much time.
OK, do what you want. Several of us with years of experience have said that we have never had the slightest bit of problems with steel bolts in long term use with aluminum chainrings. Maybe the problem is inevitable but it will not happen in any time frame that will cause you problems.

As I said, I have cranksets with over 30,000 miles that have shown no corrosive reaction between the chainrings and bolts even with exposure to rain, snow and salted roads. If that isn't long enough......
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Old 09-08-10, 09:03 AM   #14
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I'm still not convinced. I have seen plenty of rust on drive train components. Even with lubrication and maintenance, that area still collects more than its share of road grime, salty sweat, etc.
So buy some steel chainrings. Or stop worrying, and just ride the bike. You'll wear the chainrings out before they corrode. I've seen lots of bikes with all sorts of galvanic corrosion. (Seat post to seat tube, and stem to steerer usually) Never one with chainrings corroded.
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Old 09-08-10, 09:06 AM   #15
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Maybe I put too much emphasis on the bolts. Since aluminum is the anode, it will do the corroding. So you shouldn't have experienced any problems with the bolts. Ever examine the aluminum around the bolt holes to check for corrosion, wear, pitting, loss, excessive play, etc.?
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Old 09-08-10, 11:47 AM   #16
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Maybe I put too much emphasis on the bolts. Since aluminum is the anode, it will do the corroding. So you shouldn't have experienced any problems with the bolts. Ever examine the aluminum around the bolt holes to check for corrosion, wear, pitting, loss, excessive play, etc.?
You should probably just get some aluminum bolts and store it in a vat of dielectric fluid to prevent this possibility.

Or you could get the hint that it is NOT a problem and go enjoy your bike.
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Old 09-08-10, 01:00 PM   #17
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Actually, there has been no HINT given. Everyone has responsed to my question of time by citing how many miles they got out of their steel bolts. Mileage has nothing to do with it. I could build a bike and leave it sit i my garage and never ride it one time and it will be just as susceptible to galvanic reaction (minus the salty sweat drops).

Mileage is irrelevent. If you put 30,000 miles on your bike in 2 years, yeah I would expect the chainrings to wear out before galavanic corrosion set in.

If you put 1000 miles a year on your bike and want it to be in good condition 20 years from now, totally different situation.
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Old 09-08-10, 01:02 PM   #18
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Actually, there has been no HINT given. Everyone has responsed to my question of time by citing how many miles they got out of their steel bolts. Mileage has nothing to do with it. I could build a bike and leave it sit i my garage and never ride it one time and it will be just as susceptible to galvanic reaction (minus the salty sweat drops).

Mileage is irrelevent. If you put 30,000 miles on your bike in 2 years, yeah I would expect the chainrings to wear out before galavanic corrosion set in.

If you put 1000 miles a year on your bike and want to be in good condition 20 years from now, totally different situation.
What, did you just finish an Intro To Chemistry class or something? In the real world, this is NOT a problem. Chalk it up to anodized parts, chalk it up to fewer salt drops than you think, but your supposed problem simply does not exist.

God knows what will happen when you find out about all the other places steel bolts are used on aluminum throughout your bicycle.
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Old 09-08-10, 01:28 PM   #19
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Galvanic corrosion also requires the two dissimilar metals to be immersed in an electrolyte, like saltwater. For typical cycling environments. I wouldn't worry about it.
+100

But if you are really that worried about it then hang a 10# magnisium anode from your cranks or use an impress current cathodic protection system, just insulate all points of contact with your bike (especially if you have a Brooks saddle with copper rivits)

But on a serious note, you really need an electrolytic solution to have the problem.
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Old 09-08-10, 02:06 PM   #20
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My understanding is that electrolysis in these situations is more of an issue if one uses stainless steel bolts with aluminum. The Nickel content in the stainless is more electically reactive. Any Metallurgical or Electrical engineers, on the forum, care to weigh in?
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Old 09-08-10, 02:09 PM   #21
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Galvanic corrosion is an issue more with seatposts and quill stems getting stuck,
if left in a long time..

Sweated upon profusely on the trainer, indoors.

In the shipyard we welded Zinc ingots inside the tanks that were a sacrificial metal
so salt ate away that rather than the hull.

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Old 09-08-10, 07:56 PM   #22
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My understanding is that electrolysis in these situations is more of an issue if one uses stainless steel bolts with aluminum. The Nickel content in the stainless is more electically reactive. Any Metallurgical or Electrical engineers, on the forum, care to weigh in?
Yeah, that's true. Wikipedia of all places actually does a pretty good job with galvanic reaction (so all the nay-sayers can see that I'm not making this up)

http://en.wikipedia.org/wiki/Galvanic_corrosion
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Old 09-08-10, 08:28 PM   #23
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My understanding is that electrolysis in these situations is more of an issue if one uses stainless steel bolts with aluminum. The Nickel content in the stainless is more electically reactive. Any Metallurgical or Electrical engineers, on the forum, care to weigh in?
B.S., Materials Engineering. Theoretically, anything dissimilar will eventually corrode. In practice, the anodizing, lack of electrolytic solution, and grease used pretty much eliminate this as a problem within the usable lifespan of the product.
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Old 09-08-10, 08:37 PM   #24
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Yeah, that's true. Wikipedia of all places actually does a pretty good job with galvanic reaction (so all the nay-sayers can see that I'm not making this up)

http://en.wikipedia.org/wiki/Galvanic_corrosion
No one said you were making it up. What we said was it is NOT a problem in bicycle use. Yes, I have examined aluminum chainrings after YEARS of use with steel bolts. Repeat: It is NOT a problem.
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Old 09-09-10, 05:09 AM   #25
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No one said you were making it up. What we said was it is NOT a problem in bicycle use. Yes, I have examined aluminum chainrings after YEARS of use with steel bolts. Repeat: It is NOT a problem.
Then stay tuned for my next thread: "What happens when valve stem isotope atoms swap neutrons?"
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