Originally Posted by
coffeesnob
if it gets that bad a little kroil and a pipe wrench will unfreeze it
Kroil and a pipe wrench aren’t going to do anything. The problem isn’t with lubrication but with the seatpost expanding. An aluminum post that oxidizes will increase in diameter and there isn’t any room. The material formed, aluminum oxide, is harder than aluminum and it’s volume is greater. Too large a peg in too small a hole and it won’t come out.
Originally Posted by
Maelochs
I have heard it called "galvanic welding" or something .... but a seat post can bond electrically with the seat tube, and you will go through all kinds of backyard mechanical improvisations and uncivil vocabulary exercises before you get the sucker free ... and sometimes you will do irreparable harm in the process.
From what I hear .....
Yup. Or just galvanic corrosion.[size=14px] The metals can exchange electrons so there is a flow of electricity between the two metals. One will act as an anode and one will act as a cathode. Ya got a battery.[/size]
Originally Posted by
veganbikes
Because every single mechanic on the planet will want to kill you for allowing parts to seize.
For aluminum or steel posts in aluminum or steel frames use grease
For titanium use anti-seize/copper paste
For carbon posts or posts in carbon frames use carbon paste
Don't let your seatpost or any other parts get seized on any of your bikes.
Yes but for different reasons. Steel in steel aren’t dissimilar and won’t galvanically corrode. There are other issues but I’ll address them in a second. Aluminum in steel or steel in aluminum will set up a electrical potential and will corrode. A layer of grease between them is enough of an insulator to stop the flow of electrons. Aluminum in aluminum won’t corrode either. Nor will titanium in titanium nor titanium in much of anything else. Titanium is fairly inert.
Carbon paste is used with carbon posts to keep them from sliding. They won’t corrode but they are slick and will slide. The carbon paste has grit in it to keep the post from sliding.
For steel in steel and aluminum in aluminum, grease keeps another kind of corrosion down. We live in a world of salt...sweat, salt used for road clearing, and seawater being the main culprits.. The chloride ion in the salt is very reactive with both aluminum and with iron. It plucks the atoms from the metal, forms a chloride, and then exchanges the chloride for oxygen forming rust (iron oxide) in the case of iron and alumina (aluminum oxide) n the case of aluminum. The oxides formed have a greater volume than the neutral metal so the seatpost effectively expands.
The chloride, by the way, is released to go back and pluck out more metal. The whole process starts over again. Chloride also helps speed up the corrosion process when two dissimilar metals are used. Aluminum will oxidize and the steel will reduce.
Originally Posted by
bg18947
Specifically lithium grease creates a barrier between aluminum and steel (iron alloy). Whenever the outside electrons of two elements adds up to 7, an ionic bond occurs (galvanization). Same reason why you put Never-Seize on spark plugs.
Except the outer electrons for aluminum and iron don’t add up to “7”. Aluminum has an electronic configuration of [Ne[color=#000000]] 3s2
3p1, and iron has an electronic configuration of
[Ar] 3d6
4s2. Those don’t add up to 7.
Originally Posted by
50PlusCycling
The bike won't rust, but the seat post will corrode. My carbon fiber Kestrel has a seat post which is permanently frozen; corroding aluminum can bond to carbon fiber quite tenaciously.
It doesn’t “bond”. The aluminum oxide expands as noted above.
Bottom line: grease the post. It won’t hurt and it will save a lot of headache down the road.