Re: Removing a roll pin that is seized in an adjustable...
Had the exact same problem. It seems some models use a solid pin that is very difficult to remove, whereas later models us a split pin that is relatively easy to remove. I had the older model that I couldn't budge. Ended up removing the saddle clamp mechanism and taking it to a machine shop. Several forceful hits with a large hammer, a proper punch, and a table-mounted vice and it eventually moved! My advice would be to find your local machine shop and see if they can do the same for you.
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Hi, 27.2mm is a standard size for a seatpost, popular sizes includes 30.9mm om newer mountain bikes and 31.6mm on older since it stadardized to some extent. There are still many other odd sizes out there on mostly older bikes.
If you can, get a seatpost that is 27.2mm that fits directly into your frame, with no shim if possible. that will only add weight and creaks.
Also keep in mind that the length is important when you specify a seatpost. You can use websites like this to see what is possible/available before you order: Seatposts Chain Reaction Cycles
You will also have to consider if you need some setback, if the seat clamp is directly on the post, it is called a zero setback post like this:
the seat is attatched to the seatpost...the seatpost goes into the frame...just behind where it goes into the frame, there is a bolt, loosen it and the seat should move (you might have to play with it) raise it to where you need to and retighten the bolt. But make sure you don't go higher than the maximum height, it's marked on the post or you could damage the frame.
Bicycle seatposts are measured in tenths of millimeters. A typical size might be 26.4mm. Because of this you should either A) remove your old seatpost and saddle and bring it to a bike shop or B) measure the diameter of your seatpost with a pair of metric calipers, preferable digital. You can buy them for under $20 from someplace like Harbor Freight. Suspension seatposts tend to come in one (smaller diameter) size and are fittted with the appropriate size shim. Another possibility is an adjustable shim, make just for bicycle seatposts. I highly recommend your local bike shop.
Loosen the seatpost clamp and raise the seat. There is a safety line for maximum height, do not go beyond this point. If needs to be higher than safety line, get a new longer seatpost. Maybe a time for upgrade to a 16" or 20" bicycle. Lots of used ones out there and very cheap in cost.
You will have to buy a seatpost, either pivotal or railed depending on your seat. A railed seat has two rails underneath it, and needs a railed seatpost. A pivotal seat has a prism with teeth cut into it on the bottom, and requires a pivotal seatpost.
If you have a rubber mallet remove the seat from the post and loosen the bolt that secures the post in the frame. Bang the post from different angles around the top end with the mallet. Eventually you will get a small space happening where the post goes into the frame and you can spray some penetrating oil or lubricant around this gap. Eventually it will penetrate down and break the bond between the two parts. Install the seat and tighten it down enough so you can use it to twist the post back and forth or use vise grips or pliers. Remember though that if you use vicegrips or pliers that you might have to buy a new post. Keep twisting and banging the post and applying the lubricant and you should be able to get the post out. Aluminum does not rust it anodizes. It is a chemical reaction that occurs like rusting. Hope this helps.
take it to a bike shop and get a new seatpost. bike shops have manuals that they can check to find a seat post that fits the bike frame and has the proper size rails to fit your new saddle. this is a good time to upgrade the seatpost, you can get one that is lighter and more adjustable that your old one.