Friday, August 8, 2008

Reason #1 why you need to gease your seatpost...

I picked up this old Merlin bike recently. Full complement of WTB Grease Guard bits (hubs, headset, rollercams, bottom bracket) and size XL made the decision pretty easy. Not often in find such a rare bike and even rarer parts in my size. After I cleaned it up a bit, I went to raise the seat to my position and ... nope, post wouldn't budge. Put a junk seat on the post, smacked the nose with a hammer to see if it would turn. Nope, it was firmly ensconced in the seat tube. Galvanic corrosion of two dissimilar materials (aluminum and titanium in this case) had made the post and frame one. What to do?

There are a lot of "remedies" to unstick stuck seat posts available on the net. Bike upside down, coke in the seat tube is supposed to eat away at the corrosion and free the seat post. Somehow, I'm not sure if something that is supposedly safe to consume will eat away at the corrosion between two materials.

Pretty much the only reliable source of methods to unstick a stuck seat post comes from Sheldon Brown (WWSD - What Would Sheldon Do). I actually didn't read Sheldon's "15 Ways to Unstick a Seat Post" until just now, but had to chuckle because reading down the list, they were the exact methods I used in pretty much the same order.

Method: Remove seat binder completely.
Result: Seat binder removed.

Method: Slightly pry ears apart and try to twist post.
Result: Hurt my shoulder.

Method: Drip penetrating oil down slot. I had high hopes for this one because I got the bike to sit in the stand with the slot facing 12:00 and the oil was seeping into the seat tube between the post and frame a little at a time.
Result: Sheldon was right, penetrating oil is useless on aluminum corrosion.

Method: Drip ammonia into frame between seat post and seat tube. Sheldon says this method works like "magic".
Result: Didn't have ammonia so didn't try. The seat post is also an IRD and the top of the post is not liquid-tight so any liquid would have just leaked out. Would have liked to see "magic" work, though.

Method: Heat seat tube area.
Result: Using a propane torch, I heated the seat tube area slowly and evenly. At first, the penetration oil started burning off and then there was some creaking which I assume was the titanium expanding from the aluminum post essentially freeing itself from the grasp of the corrosion. I also blasted a 16g CO2 cartridge at the seat post (actually 4 of them). As the CO2 cartridge is expended at the post, the air coming out is really cold. The idea here as the heat expanded the material, the CO2 contracts it. Post procedure, I see on Sheldon's website that this procedure is useless on aluminum posts stuck in titanium frames becasue aluminum expands at as much as 2.5 times the rate of titanium effectively making the aluminum post even tighter in the frame. Maybe, but after shooting off 4 cartridges, and smacking the nose of the seat with a hammer, the post moved! After it moved I wondered if it was actually the top of the seat post (which is bonded/pressed into the shaft on an IRD post) was twisting in the shaft. I used a Sharpie to make a line across both parts to see if I'd broken the post. Nope, the whole seat post was turning! A few more whacks and I was then able to use my hands and twist the post out. Finally!

I'm not sure if it was the heat, the cold, or the combination that eventually freed the post, but at this point, it's out and that's all that matters. Probably should have tried just the cold first, but I really wanted to fire up the torch.

Method: Cut the seat post about an inch above the seat tube (Sheldon says 1/2", but I like to have a bit more post exposed to grab after the next step), and then using just the blade, cut into the inside of the post length-wise making a slot in the post.
Result: With the slot cut in the seat post, you can effectively collaps the seat post to a smaller diameter and pull it out. I know this one works because I've had to do it on on a few bikes. It's a pain and takes a while, but it's the last resort. I really wanted to avoid this method on this bike, not because I wanted to save the vintage IRD seat post, but because there was well over half of a 350mm seat post down in the frame - that's a lot of seat post to cut with a hack saw blade held in your hand.

The tools of the job and the end reslut.


Nope, the top didn't turn.


The corrosion was so bad on the post, that there are some pretty good "holes" in the post.


(What's playing: Colin Linden Spirit of the Golden Tone on KPIG)

4 comments:

Jim G said...

photos of the bike! photos of the bike! ;)

blackmountaincycles said...

Soon. I've got to do some more clean up. The old grease guard bearings in the bb have bitten the dust. I need to put in some Phils since the GG bearings are long gone. And I need to install a more respectable forged type crank. I'm not a fan of spindly CNC cranks.

Guitar Ted said...

Nice find, butyeah....definitely need to see this when you are ready.

So, you resorted to the ol' "hot wrench", eh? I don't suppose that's an option with an aluminum or carbon fiber frame.

In a similar manner to yours, I read once where some mechanics dropped some dry ice down through the bottom bracket shell which (I suppose) made its way into the open end of the seat post while they used a heat gun on the outside. The story goes that it popped right out.

Nice story at any rate. :-)

blackmountaincycles said...

Dry ice or amonia through the bb shell wasn't much of an option since the bearings are pressed in and I didn't really want to mess with those until I figure out what crankset I ultimately want on the bike.