peripatetic

The seatpost on my Trek was in the seattube quite tight, and in the process of taking it out in order to grease it, the alloy got scraped up, with all those unsightly scars criss-crossing it.

Is there some special grease to use to avoid those scar lines? Why is it almost inevitable that they show up on a beautiful, shiny new seatpost?!

And is there any way to polish such ugliness away? I've tried filing before, but it just made the scrapes more uniform. Maybe I need a finer-textured file?

well biked

We don't want to hear another word from you about seatposts until you report that you've gotten the Laprade out of the Miyata. .............Seriously, though, just take some 220 grit sandpaper and you should be able to get rid of most of the crisscross marks on your post. Usually, just this bit of sanding will make the seatpost go in much smoother next time. Slather grease in the seat tube before installation-

peripatetic

Hey, considering it's going to take a shopful of power tools and a lab full of caustic chemicals, and I'm just starting a new semester of school, it's going to take a bit! Patience--baby steps, eh?

But thanks for the sandpaper advice. I knew my file was just a little too hefty !

unworthy1

But take care of the cause, not just the symptoms: the reason you got the zig-zags is there's some sharp edge in the seat tube that's scratching the post. I have an adjustable reamer (just $15 at use-Enco.com) but you could also try wrapping/taping sandpaper around a big dowel or piece of broomstick. It will take longer to sand, but eventually you'll see where the high spot is and can concentrate your efforts. I've also used a flexhone and a brake cylinder type hone, but once you have a reamer....(note you want to get the size "H", and even though it's a cheapo import, it's a tool I use constantly and always with cutting fluid)

peripatetic

What's cutting fluid?

<edit> I checked out reamers at use-enco.com, as you suggested. But exactly how are they used? You hold them with your hand, or attach them to a drill or something? The pics aren't very instructive. <edit>

unworthy1

You're supposed to use a big tap handle with these reamers, but I just grab the end with a big visegrip. (my tap handles are all small and I didn't want to invest just for this tool) Whatever you use DON'T let the reamer slde down into the seat tube, you might never get it out. Cutting fluid means some kind of lubricant that floats the chips away from the point of actual work when you cut or tap metal, and it's also vital for preserving the edge of the tool. You'd want cutting oil if working on steel or iron, and a lighter substance if cutting aluminum or other nonferrous metals. I use Tap Magic (nonferrous formula) for this but don't really know what's in it, they don't say. A little goes a long way. In a pinch, anything is better than cutting or drilling "dry", even WD40 will work. Using an adjustable reamer is slow hand work, you don't want to rush or remove enough metal to require a bigger seatpost (unless that IS your goal). Just adjust the reamer to fit snugly but still allow hand turning, oil it up, turn away, remove and adjust the blades little "bigger" diameter...repeat as needed. From what I've seen, the adjustable reamer is THE TOOL that framebuilders all use to dress a seat tube, but they buy the high quality $80 jobs.

peripatetic

Well, so, I sanded the post down just a bit, and lubed it up. I then went and wiped out the inside of the tube with a towel and looked inside with my flashlight. The inside of the tube is in perfect condition, without any imperfections or scratches or anything. Anyway, I lubed in there, slathered more grease on the inside, and put the 'post in. It was still very tight. I tried not to twist it too much, but rather push. It went in, but as I said, it was very tight. I really need to use a reamer? This is the bike I posted the other day, an '86 Trek that's seen very little use. Seems strange that I'd need to ream something that's basically in like-new/mint condition.

Also, could a metal shop or LBS do work like this for me? We're talking a very slight "cleaning," right?

well biked

I'd do a little more sanding on the seatpost, wrap the sandpaper around the post and sand the whole surface that's getting inserted. Check periodically as you sand and see if it's any easier to insert. If when you say "very tight," you mean you're really having to struggle to get it to go in at all, you've probably got a post that's something like .2mm too large-

you

A lot of bike chops "deburr" the inside of seat tubes on new bikes by just taking a file to the inside of them, try that.

peripatetic

Well, it is a bit hard to insert. But this is the thing: I really don't think the bike could be any less used. I mean, I get the impression that the original owner bought it for one bike tour, then never rode it again. In fact, from what I saw of pulling the post out, I got the impression that the post may never have been removed after the initial adjustment.

I thought the post was stuck b/c it just hadn't been moved in something like 10 years and was maybe starting to bond to the inside of the tube, but now that I tried to re-insert it, I don't think that's the case.

I'll do as you say, and continue lightly polishing with the sandpaper, which is a little sad, because you can still see the tiny horizontal grooves originally in the post. But if that doesn't work, then maybe the bike shop that sold the guy the bike just didn't outfit it with the proper seatpost...

As far as the inside of the seattube, I mean, looking in with the flashlight, it's pristine, smooth steel, no rust, no specks, no burrs, etc.

Pompiere

If I remember correctly, Tap-Magic is mainly trichlorethane.

unworthy1

not anymore. It's been reformulated and 1,1,1-trichloroethane is gone. That stuff is ozone-depleting, but whatever is in there now is very OSHA friendly, they make it seem like you can practically drink it...still smells foul to me, tho.

robtown

Got the same squigglies on the 33 year old alloy seatpost. I polished it up with emery cloth and re-inserted with some greese. I may have to repeat because I'd like to change out seatpost & saddle combos.