bane

The seat post is slightly loose even with the binder bolt tightened as much as possible. There is no more space in between the two sides of the notch at the top of the seat tube. The seat post I have is not marked with a size. Anyone know what size seat post this bike should take? If not I'm going to get it measured at the lbs. In addition, do I need to spread out the two sides of the seat post clamp? Here's a picture, fuzzy, of the area when the seat post binder bolt is loose showing the two sides of the seat post clamp pressed together.

EjustE

What size seat post are you using right now and is loose? What bike is it (so someone here can figure the original seat post size) ?

That said, the easiest way to take care of it is to get a seat post .2mm larger than the one you are using now and call it a day (unless you are using a 27.2 mm seatpost)

bane

The bike is a a 531 tubed Wizard, I just got an email from Mike Howard (one of the two builders) and he says that almost all of them were built for 27.2 seat posts.

The seat post I have now is not marked. I don't have calipers to measure it. Eyeballing it against a ruler it looks like the seatpost I have is 25 or 26mm, but that is obviously not precise.

Chombi

Drop the tools and don't try to tighten the seatpost clamp any more. The seatpost is definitely undersized if the gap on the split on the tube had already bottomed out and the post is still loose. You should release all the tension on tht binder bolt asap (before the seat cluster lug gets damaged) and restore the gap at the split on the tube so the cut ends are parallel again and then measure the opening on the tube to figure out the dcorrect seatpost diameter you will need.

Chombi

mkeller234

It sounds like you will be hunting for a new seat post. I would err on the side of caution with a nice frame like that one.

bane

I'm going to have to see a builder or mechanic because a 27.2 definitely will not fit in the seat tube.

unworthy1

good idea...chances are good that it's got a deformed opening, now, maybe ovalized, and it'll need to have the slot spread back to where it should be and the opening be made round again. A good shop or builder will get this made right, and can measure the tube with the proper tool and ream the tube if needed.

randyjawa 

The collapsed seat post lug gap is a fairly common problem with old road bikes, in my opinion. Here is how I deal with this problem...

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

Hope this is a help.

miamijim

lossen the bolt all the way and lean back on the existing post. It'll open it back up.

norskagent

Just widening and straightening the gap may or may not work. My '85 bianchi track bike has the same issue, apparently someone used a smaller spec seatpost in it at one time, which pinched the tube slot. It takes a 26.8mm seatpost, but it would slip even after I straightened the slot out. I ended up filing (actually sandpaper) the slot opening a tiny amount so it wouldn't pinch when tightened, which seems to work. Also, you can try different seatposts of the same size (once you figure out the right size), as they are not all exactly the same despite what they say.

due ruote 

Wrap a strip of paper as tightly as you can around the seatpost and mark where it crosses with a sharp knife. Unwrap the paper and measure the distance in mm; divide that by pi for the diameter.

bane

Nice, I forgot about that awesome toolbox we call math.

due ruote 

See? And you told your HS geometry teacher you were never going to use that.

JohnDThompson 

If the seat lug is deformed I don't recommend reaming to fix it. Usually you can spread it back to the proper shape without too much trouble -- this is a steel frame, after all.