I'm in the middle of restoring a 1983 Trek 520. I bought a new seatpost to replace the old one and I'm having a lot of trouble getting it to 'fit.' I have it in the correct size but I can barely get it to fit down into the seat tube. I'm greasing it and everything but I'm fighting it just trying to get it to slide in.

The original post was very very short, and the new one is long.. which makes me think that for some reason since the old post was barely inserted into the tube is why the new longer post is so difficult to get in - like it hasn't been stretched out enough or something for it to fit very well.

Does this make sense? Anyone ever have similar issues w/ an older frame? If so, could someone give me some pointers on how to get it to fit better? It feels like I almost need to spread it out slightly..I wish that were easy..haha. Any help is much appreciated, thanks!

Is this a large sized frame? Can you see if there's something stuck down into the seat tube?

It's a 56cm frame, and nothing is stuck in the seat tube. I can get it to kind of slide in but it's incredibly tight and I'm fighting it to get it down in there. I'm a bit afraid it will never come out again..

In this instance, the options would seem to be to either ream the seat post, or get a seat post that's .2mm narrower.

Out of curiosity, how did you determine the correct size?

The size was listed in the original specs, and it was the same size as the original post.

I had been thinking of trying out a slightly narrower post, just thought I'd check if there were other options I could try first before buying a 2nd brand-new post

lube is your friend. Never slide an unlubed seat post down the seat tube. Any non-water soluble lubricant (even cheap petroleum jelly) would do. SPs should be tight.

E is correct, but if pushing and twisting with a saddle on isn't enough to get a lubricated post in, either the opening is deformed, or you're going to need a smaller post.

+1 on that. Be certain you have the right size to begin with.

Having established that, you may want to check the seat binder slot for any deformation.

Also, if you are installing one of those aftermarket alloy posts, be advised that these can be long enough ( ~ 350 mm) to do double duty on MTBs. There is no need to have 12" of engagement on an old road bike, and you are correct in assuming that this only increases the prospects for a stuck seat post down the line. You ought to cut it down to the appropriate length and debur it - and then grease the Dickens out of it!

Would .4mm narrower be too much of a difference?

Yes

Yeah.

I have to double check, but I think that the 83 520s were build with Reynolds 501 and take a 26.8 seatpost. What size is the one you are trying to put in?

+1000, better to use a smaller post than ruin the frame by forcing "the right size" post into the tube, and remember, just 'cause the specs show one size doesn't mean it's not another.

OP says: "I'm greasing it and everything but I'm fighting it just trying to get it to slide in." ;0)

Another possibility is that there is rust on the inside diameter of the seat tube below the level where the old seat post was. = Another reason why it would be wise to cut it down to a reasonable length.

I have ran into this more than once, I bet this is the issue. A brake hone and bastard file should take care of it. Miamijim has a thread on it.

Jake

There has been a recall on 520 frames in the 56cm size: The lugs separate from the frame and then the seat stays curl and pop. You have send it to the steel trek recall center. Please PM me for the address to mail it to.

funny

Have you measured the old and new seatposts to see if they are actually the same size (diameter)? Sometimes seatposts are not made exactly right and are a little off in their sizing. Also, is it hard to insert right away at the top? I had a Mercier like this, and the problem was that the seat tube had been squeezed together and distorted due to overtightening of the binder bolt. I had to spread it apart and file the inside of the tube. Once I did this, the seatpost went in easily. Finally, don't always believe manufacturer specs. I recently received a frame that was spec'd for a 27.2mm seatpost, and it turned out to be 27.4mm.

Time to go see your friendly machine shop.
Why screw around?
Bill

That's what she said.

Not sure if this will help but I have written an article on frame set cavities(seat post, steering and bottom bracket) and how to ensure that they are well prepared prior to refinishing or reworking a frame set. Have a look and something here might prove to be a help.

https://www.mytenspeeds.com/My_TenSpe...CavityPrep.htm